[PATCH 13/19] gfs2: Convert to new freezing mechanism

[PATCH 13/19] gfs2: Convert to new freezing mechanism

[Jan Kara]

It is enough to update gfs2_page_mkwrite() to use new freeze protection.
Rest is handled by the generic code.

CC: cluster-devel@redhat.com
CC: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/gfs2/file.c |   15 +++------------
 1 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index 1f03531..806b7a4 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -369,11 +369,7 @@ static int gfs2_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	loff_t size;
 	int ret;
 
-	/* Wait if fs is frozen. This is racy so we check again later on
-	 * and retry if the fs has been frozen after the page lock has
-	 * been acquired
-	 */
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
+	sb_start_pagefault(inode->i_sb);
 
 	/* Update file times before taking page lock */
 	file_update_time(vma->vm_file);
@@ -457,14 +453,9 @@ out:
 	gfs2_holder_uninit(&gh);
 	if (ret == 0) {
 		set_page_dirty(page);
-		/* This check must be post dropping of transaction lock */
-		if (inode->i_sb->s_frozen == SB_UNFROZEN) {
-			wait_on_page_writeback(page);
-		} else {
-			ret = -EAGAIN;
-			unlock_page(page);
-		}
+		wait_on_page_writeback(page);
 	}
+	sb_end_pagefault(inode->i_sb);
 	return block_page_mkwrite_return(ret);
 }
 
-- 
1.7.1

[PATCH 00/19 v4] Fix filesystem freezing deadlocks

[Jan Kara]

  Hello,

  here is the fourth iteration of my patches to improve filesystem freezing.
Filesystem freezing is currently racy and thus we can end up with dirty data on
frozen filesystem (see changelog patch 06 for detailed race description). This
patch series aims at fixing this.

To be able to block all places where inodes get dirtied, I've moved filesystem
freeze handling in mnt_want_write() / mnt_drop_write(). This however required
some code shuffling and changes to kern_path_create() (see patches 02-05). I
think the result is OK but opinions may differ ;). The advantage of this change
also is that all filesystems get freeze protection almost for free - even ext2
can handle freezing well now.

Another potential contention point might be patch 19. In that patch we make
freeze_super() refuse to freeze the filesystem when there are open but unlinked
files which may be impractical in some cases. The main reason for this is the
problem with handling of file deletion from fput() called with mmap_sem held
(e.g. from munmap(2)), and then there's the fact that we cannot really force
such filesystem into a consistent state... But if people think that freezing
with open but unlinked files should happen, then I have some possible
solutions in mind (maybe as a separate patchset since this is large enough).

I'm not able to hit any deadlocks, lockdep warnings, or dirty data on frozen
filesystem despite beating it with fsstress and bash-shared-mapping while
freezing and unfreezing for several hours (using ext4 and xfs) so I'm
reasonably confident this could finally be the right solution.

And for people wanting to test - this patchset is based on patch series
"Push file_update_time() into .page_mkwrite" so you'll need to pull that one
in as well.

Changes since v3:
  * added third level of freezing for fs internal purposes - hooked some
    filesystems to use it (XFS, nilfs2)
  * removed racy i_size check from filemap_mkwrite()

Changes since v2:
  * completely rewritten
  * freezing is now blocked at VFS entry points
  * two stage freezing to handle both mmapped writes and other IO

The biggest changes since v1:
  * have two counters to provide safe state transitions for SB_FREEZE_WRITE
    and SB_FREEZE_TRANS states
  * use percpu counters instead of own percpu structure
  * added documentation fixes from the old fs freezing series
  * converted XFS to use SB_FREEZE_TRANS counter instead of its private
    m_active_trans counter

								Honza

CC: Alex Elder <elder-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
CC: Anton Altaparmakov <anton-yrGDUoBaLx3QT0dZR+AlfA@public.gmane.org>
CC: Ben Myers <bpm-sJ/iWh9BUns@public.gmane.org>
CC: Chris Mason <chris.mason-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
CC: cluster-devel-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org
CC: "David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>
CC: fuse-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
CC: "J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>
CC: Joel Becker <jlbec-aKy9MeLSZ9dg9hUCZPvPmw@public.gmane.org>
CC: KONISHI Ryusuke <konishi.ryusuke-Zyj7fXuS5i5L9jVzuh4AOg@public.gmane.org>
CC: linux-btrfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
CC: linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
CC: linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
CC: linux-nilfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
CC: linux-ntfs-dev-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
CC: Mark Fasheh <mfasheh-IBi9RG/b67k@public.gmane.org>
CC: Miklos Szeredi <miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org>
CC: ocfs2-devel-N0ozoZBvEnrZJqsBc5GL+g@public.gmane.org
CC: OGAWA Hirofumi <hirofumi-UIVanBePwB70ZhReMnHkpc8NsWr+9BEh@public.gmane.org>
CC: Steven Whitehouse <swhiteho-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
CC: "Theodore Ts'o" <tytso-3s7WtUTddSA@public.gmane.org>
CC: xfs-VZNHf3L845pBDgjK7y7TUQ@public.gmane.org
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[PATCH 01/19] mm: Make default vm_ops provide ->page_mkwrite handler

[Jan Kara]

Make default vm_ops provide ->page_mkwrite handler. Currently it only updates
file's modification times and gets locked page but later it will also handle
filesystem freezing.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 include/linux/mm.h |    1 +
 mm/filemap.c       |   19 +++++++++++++++++++
 mm/filemap_xip.c   |    1 +
 3 files changed, 21 insertions(+), 0 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 17b27cd..074c075 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1419,6 +1419,7 @@ extern void truncate_inode_pages_range(struct address_space *,
 
 /* generic vm_area_ops exported for stackable file systems */
 extern int filemap_fault(struct vm_area_struct *, struct vm_fault *);
+extern int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
 
 /* mm/page-writeback.c */
 int write_one_page(struct page *page, int wait);
diff --git a/mm/filemap.c b/mm/filemap.c
index b662757..fbd69e3 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1759,8 +1759,27 @@ page_not_uptodate:
 }
 EXPORT_SYMBOL(filemap_fault);
 
+int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+	struct page *page = vmf->page;
+	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
+	int ret = VM_FAULT_LOCKED;
+
+	file_update_time(vma->vm_file);
+	lock_page(page);
+	if (page->mapping != inode->i_mapping) {
+		unlock_page(page);
+		ret = VM_FAULT_NOPAGE;
+		goto out;
+	}
+out:
+	return ret;
+}
+EXPORT_SYMBOL(filemap_page_mkwrite);
+
 const struct vm_operations_struct generic_file_vm_ops = {
 	.fault		= filemap_fault,
+	.page_mkwrite	= filemap_page_mkwrite,
 };
 
 /* This is used for a general mmap of a disk file */
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index a4eb311..591dba6 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -304,6 +304,7 @@ out:
 
 static const struct vm_operations_struct xip_file_vm_ops = {
 	.fault	= xip_file_fault,
+	.page_mkwrite	= filemap_page_mkwrite,
 };
 
 int xip_file_mmap(struct file * file, struct vm_area_struct * vma)
-- 
1.7.1

[PATCH 02/19] fs: Push mnt_want_write() outside of i_mutex

[Jan Kara]

Currently, mnt_want_write() is sometimes called with i_mutex held and sometimes
without it. This isn't really a problem because mnt_want_write() is a
non-blocking operation (essentially has a trylock semantics) but when the
function starts to handle also frozen filesystems, it will get a full lock
semantics and thus proper lock ordering has to be established. So move
all mnt_want_write() calls outside of i_mutex.

One non-trivial case needing conversion is kern_path_create() /
user_path_create() which didn't include mnt_want_write() but now needs to
because it acquires i_mutex.  Because there are virtual file systems which
don't bother with freeze / remount-ro protection we actually provide both
versions of the function - one which calls mnt_want_write() and one which does
not.

CC: ocfs2-devel@oss.oracle.com
CC: Mark Fasheh <mfasheh@suse.com>
CC: Joel Becker <jlbec@evilplan.org>
CC: "David S. Miller" <davem@davemloft.net>
BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/namei.c              |  115 +++++++++++++++++++++++++++--------------------
 fs/ocfs2/refcounttree.c |   10 +---
 include/linux/namei.h   |    2 +
 net/unix/af_unix.c      |   13 ++----
 4 files changed, 74 insertions(+), 66 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index a780ea5..575d3a4 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2383,7 +2383,9 @@ struct file *do_file_open_root(struct dentry *dentry, struct vfsmount *mnt,
 	return file;
 }
 
-struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path, int is_dir)
+static struct dentry *do_kern_path_create(int dfd, const char *pathname,
+					  struct path *path, int is_dir,
+					  int freeze_protect)
 {
 	struct dentry *dentry = ERR_PTR(-EEXIST);
 	struct nameidata nd;
@@ -2401,6 +2403,14 @@ struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path
 	nd.flags |= LOOKUP_CREATE | LOOKUP_EXCL;
 	nd.intent.open.flags = O_EXCL;
 
+	if (freeze_protect) {
+		error = mnt_want_write(nd.path.mnt);
+		if (error) {
+			dentry = ERR_PTR(error);
+			goto out;
+		}
+	}
+
 	/*
 	 * Do the final lookup.
 	 */
@@ -2429,24 +2439,49 @@ eexist:
 	dentry = ERR_PTR(-EEXIST);
 fail:
 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
+	if (freeze_protect)
+		mnt_drop_write(nd.path.mnt);
 out:
 	path_put(&nd.path);
 	return dentry;
 }
+
+struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path, int is_dir)
+{
+	return do_kern_path_create(dfd, pathname, path, is_dir, 0);
+}
 EXPORT_SYMBOL(kern_path_create);
 
+struct dentry *kern_path_create_thawed(int dfd, const char *pathname, struct path *path, int is_dir)
+{
+	return do_kern_path_create(dfd, pathname, path, is_dir, 1);
+}
+EXPORT_SYMBOL(kern_path_create_thawed);
+
 struct dentry *user_path_create(int dfd, const char __user *pathname, struct path *path, int is_dir)
 {
 	char *tmp = getname(pathname);
 	struct dentry *res;
 	if (IS_ERR(tmp))
 		return ERR_CAST(tmp);
-	res = kern_path_create(dfd, tmp, path, is_dir);
+	res = do_kern_path_create(dfd, tmp, path, is_dir, 0);
 	putname(tmp);
 	return res;
 }
 EXPORT_SYMBOL(user_path_create);
 
+struct dentry *user_path_create_thawed(int dfd, const char __user *pathname, struct path *path, int is_dir)
+{
+	char *tmp = getname(pathname);
+	struct dentry *res;
+	if (IS_ERR(tmp))
+		return ERR_CAST(tmp);
+	res = do_kern_path_create(dfd, tmp, path, is_dir, 1);
+	putname(tmp);
+	return res;
+}
+EXPORT_SYMBOL(user_path_create_thawed);
+
 int vfs_mknod(struct inode *dir, struct dentry *dentry, umode_t mode, dev_t dev)
 {
 	int error = may_create(dir, dentry);
@@ -2502,7 +2537,7 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
 	if (S_ISDIR(mode))
 		return -EPERM;
 
-	dentry = user_path_create(dfd, filename, &path, 0);
+	dentry = user_path_create_thawed(dfd, filename, &path, 0);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
 
@@ -2511,12 +2546,9 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
 	error = may_mknod(mode);
 	if (error)
 		goto out_dput;
-	error = mnt_want_write(path.mnt);
-	if (error)
-		goto out_dput;
 	error = security_path_mknod(&path, dentry, mode, dev);
 	if (error)
-		goto out_drop_write;
+		goto out_dput;
 	switch (mode & S_IFMT) {
 		case 0: case S_IFREG:
 			error = vfs_create(path.dentry->d_inode,dentry,mode,NULL);
@@ -2529,11 +2561,10 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
 			error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
 			break;
 	}
-out_drop_write:
-	mnt_drop_write(path.mnt);
 out_dput:
 	dput(dentry);
 	mutex_unlock(&path.dentry->d_inode->i_mutex);
+	mnt_drop_write(path.mnt);
 	path_put(&path);
 
 	return error;
@@ -2571,24 +2602,20 @@ SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
 	struct path path;
 	int error;
 
-	dentry = user_path_create(dfd, pathname, &path, 1);
+	dentry = user_path_create_thawed(dfd, pathname, &path, 1);
 	if (IS_ERR(dentry))
 		return PTR_ERR(dentry);
 
 	if (!IS_POSIXACL(path.dentry->d_inode))
 		mode &= ~current_umask();
-	error = mnt_want_write(path.mnt);
-	if (error)
-		goto out_dput;
 	error = security_path_mkdir(&path, dentry, mode);
 	if (error)
-		goto out_drop_write;
+		goto out_dput;
 	error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
-out_drop_write:
-	mnt_drop_write(path.mnt);
 out_dput:
 	dput(dentry);
 	mutex_unlock(&path.dentry->d_inode->i_mutex);
+	mnt_drop_write(path.mnt);
 	path_put(&path);
 	return error;
 }
@@ -2683,6 +2710,9 @@ static long do_rmdir(int dfd, const char __user *pathname)
 	}
 
 	nd.flags &= ~LOOKUP_PARENT;
+	error = mnt_want_write(nd.path.mnt);
+	if (error)
+		goto exit1;
 
 	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 	dentry = lookup_hash(&nd);
@@ -2693,19 +2723,15 @@ static long do_rmdir(int dfd, const char __user *pathname)
 		error = -ENOENT;
 		goto exit3;
 	}
-	error = mnt_want_write(nd.path.mnt);
-	if (error)
-		goto exit3;
 	error = security_path_rmdir(&nd.path, dentry);
 	if (error)
-		goto exit4;
+		goto exit3;
 	error = vfs_rmdir(nd.path.dentry->d_inode, dentry);
-exit4:
-	mnt_drop_write(nd.path.mnt);
 exit3:
 	dput(dentry);
 exit2:
 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
+	mnt_drop_write(nd.path.mnt);
 exit1:
 	path_put(&nd.path);
 	putname(name);
@@ -2772,6 +2798,9 @@ static long do_unlinkat(int dfd, const char __user *pathname)
 		goto exit1;
 
 	nd.flags &= ~LOOKUP_PARENT;
+	error = mnt_want_write(nd.path.mnt);
+	if (error)
+		goto exit1;
 
 	mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
 	dentry = lookup_hash(&nd);
@@ -2784,21 +2813,17 @@ static long do_unlinkat(int dfd, const char __user *pathname)
 		if (!inode)
 			goto slashes;
 		ihold(inode);
-		error = mnt_want_write(nd.path.mnt);
-		if (error)
-			goto exit2;
 		error = security_path_unlink(&nd.path, dentry);
 		if (error)
-			goto exit3;
+			goto exit2;
 		error = vfs_unlink(nd.path.dentry->d_inode, dentry);
-exit3:
-		mnt_drop_write(nd.path.mnt);
-	exit2:
+exit2:
 		dput(dentry);
 	}
 	mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 	if (inode)
 		iput(inode);	/* truncate the inode here */
+	mnt_drop_write(nd.path.mnt);
 exit1:
 	path_put(&nd.path);
 	putname(name);
@@ -2858,23 +2883,19 @@ SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
 	if (IS_ERR(from))
 		return PTR_ERR(from);
 
-	dentry = user_path_create(newdfd, newname, &path, 0);
+	dentry = user_path_create_thawed(newdfd, newname, &path, 0);
 	error = PTR_ERR(dentry);
 	if (IS_ERR(dentry))
 		goto out_putname;
 
-	error = mnt_want_write(path.mnt);
-	if (error)
-		goto out_dput;
 	error = security_path_symlink(&path, dentry, from);
 	if (error)
-		goto out_drop_write;
+		goto out_dput;
 	error = vfs_symlink(path.dentry->d_inode, dentry, from);
-out_drop_write:
-	mnt_drop_write(path.mnt);
 out_dput:
 	dput(dentry);
 	mutex_unlock(&path.dentry->d_inode->i_mutex);
+	mnt_drop_write(path.mnt);
 	path_put(&path);
 out_putname:
 	putname(from);
@@ -2964,7 +2985,7 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
 	if (error)
 		return error;
 
-	new_dentry = user_path_create(newdfd, newname, &new_path, 0);
+	new_dentry = user_path_create_thawed(newdfd, newname, &new_path, 0);
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry))
 		goto out;
@@ -2972,18 +2993,14 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
 	error = -EXDEV;
 	if (old_path.mnt != new_path.mnt)
 		goto out_dput;
-	error = mnt_want_write(new_path.mnt);
-	if (error)
-		goto out_dput;
 	error = security_path_link(old_path.dentry, &new_path, new_dentry);
 	if (error)
-		goto out_drop_write;
+		goto out_dput;
 	error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry);
-out_drop_write:
-	mnt_drop_write(new_path.mnt);
 out_dput:
 	dput(new_dentry);
 	mutex_unlock(&new_path.dentry->d_inode->i_mutex);
+	mnt_drop_write(new_path.mnt);
 	path_put(&new_path);
 out:
 	path_put(&old_path);
@@ -3174,6 +3191,10 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
 	if (newnd.last_type != LAST_NORM)
 		goto exit2;
 
+	error = mnt_want_write(oldnd.path.mnt);
+	if (error)
+		goto exit2;
+
 	oldnd.flags &= ~LOOKUP_PARENT;
 	newnd.flags &= ~LOOKUP_PARENT;
 	newnd.flags |= LOOKUP_RENAME_TARGET;
@@ -3209,23 +3230,19 @@ SYSCALL_DEFINE4(renameat, int, olddfd, const char __user *, oldname,
 	if (new_dentry == trap)
 		goto exit5;
 
-	error = mnt_want_write(oldnd.path.mnt);
-	if (error)
-		goto exit5;
 	error = security_path_rename(&oldnd.path, old_dentry,
 				     &newnd.path, new_dentry);
 	if (error)
-		goto exit6;
+		goto exit5;
 	error = vfs_rename(old_dir->d_inode, old_dentry,
 				   new_dir->d_inode, new_dentry);
-exit6:
-	mnt_drop_write(oldnd.path.mnt);
 exit5:
 	dput(new_dentry);
 exit4:
 	dput(old_dentry);
 exit3:
 	unlock_rename(new_dir, old_dir);
+	mnt_drop_write(oldnd.path.mnt);
 exit2:
 	path_put(&newnd.path);
 	putname(to);
diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
index cf78233..a99b8e2 100644
--- a/fs/ocfs2/refcounttree.c
+++ b/fs/ocfs2/refcounttree.c
@@ -4453,7 +4453,7 @@ int ocfs2_reflink_ioctl(struct inode *inode,
 		return error;
 	}
 
-	new_dentry = user_path_create(AT_FDCWD, newname, &new_path, 0);
+	new_dentry = user_path_create_thawed(AT_FDCWD, newname, &new_path, 0);
 	error = PTR_ERR(new_dentry);
 	if (IS_ERR(new_dentry)) {
 		mlog_errno(error);
@@ -4466,19 +4466,13 @@ int ocfs2_reflink_ioctl(struct inode *inode,
 		goto out_dput;
 	}
 
-	error = mnt_want_write(new_path.mnt);
-	if (error) {
-		mlog_errno(error);
-		goto out_dput;
-	}
-
 	error = ocfs2_vfs_reflink(old_path.dentry,
 				  new_path.dentry->d_inode,
 				  new_dentry, preserve);
-	mnt_drop_write(new_path.mnt);
 out_dput:
 	dput(new_dentry);
 	mutex_unlock(&new_path.dentry->d_inode->i_mutex);
+	mnt_drop_write(new_path.mnt);
 	path_put(&new_path);
 out:
 	path_put(&old_path);
diff --git a/include/linux/namei.h b/include/linux/namei.h
index ffc0213..432f6bb 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -77,7 +77,9 @@ extern int user_path_at_empty(int, const char __user *, unsigned, struct path *,
 extern int kern_path(const char *, unsigned, struct path *);
 
 extern struct dentry *kern_path_create(int, const char *, struct path *, int);
+extern struct dentry *kern_path_create_thawed(int, const char *, struct path *, int);
 extern struct dentry *user_path_create(int, const char __user *, struct path *, int);
+extern struct dentry *user_path_create_thawed(int, const char __user *, struct path *, int);
 extern int kern_path_parent(const char *, struct nameidata *);
 extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
 			   const char *, unsigned int, struct path *);
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 85d3bb7..7888b09 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -856,7 +856,7 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		 * Get the parent directory, calculate the hash for last
 		 * component.
 		 */
-		dentry = kern_path_create(AT_FDCWD, sun_path, &path, 0);
+		dentry = kern_path_create_thawed(AT_FDCWD, sun_path, &path, 0);
 		err = PTR_ERR(dentry);
 		if (IS_ERR(dentry))
 			goto out_mknod_parent;
@@ -866,19 +866,13 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
 		 */
 		mode = S_IFSOCK |
 		       (SOCK_INODE(sock)->i_mode & ~current_umask());
-		err = mnt_want_write(path.mnt);
-		if (err)
-			goto out_mknod_dput;
 		err = security_path_mknod(&path, dentry, mode, 0);
 		if (err)
-			goto out_mknod_drop_write;
-		err = vfs_mknod(path.dentry->d_inode, dentry, mode, 0);
-out_mknod_drop_write:
-		mnt_drop_write(path.mnt);
-		if (err)
 			goto out_mknod_dput;
+		err = vfs_mknod(path.dentry->d_inode, dentry, mode, 0);
 		mutex_unlock(&path.dentry->d_inode->i_mutex);
 		dput(path.dentry);
+		mnt_drop_write(path.mnt);
 		path.dentry = dentry;
 
 		addr->hash = UNIX_HASH_SIZE;
@@ -916,6 +910,7 @@ out:
 out_mknod_dput:
 	dput(dentry);
 	mutex_unlock(&path.dentry->d_inode->i_mutex);
+	mnt_drop_write(path.mnt);
 	path_put(&path);
 out_mknod_parent:
 	if (err == -EEXIST)
-- 
1.7.1

[PATCH 03/19] fat: Push mnt_want_write() outside of i_mutex

[Jan Kara]

When mnt_want_write() starts to handle freezing it will get a full lock
semantics requiring proper lock ordering. So push mnt_want_write() call
outside of i_mutex as in other places.

CC: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/fat/file.c |   15 +++++++--------
 1 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/fs/fat/file.c b/fs/fat/file.c
index a71fe37..e007b8b 100644
--- a/fs/fat/file.c
+++ b/fs/fat/file.c
@@ -43,10 +43,10 @@ static int fat_ioctl_set_attributes(struct file *file, u32 __user *user_attr)
 	if (err)
 		goto out;
 
-	mutex_lock(&inode->i_mutex);
 	err = mnt_want_write_file(file);
 	if (err)
-		goto out_unlock_inode;
+		goto out;
+	mutex_lock(&inode->i_mutex);
 
 	/*
 	 * ATTR_VOLUME and ATTR_DIR cannot be changed; this also
@@ -73,14 +73,14 @@ static int fat_ioctl_set_attributes(struct file *file, u32 __user *user_attr)
 	/* The root directory has no attributes */
 	if (inode->i_ino == MSDOS_ROOT_INO && attr != ATTR_DIR) {
 		err = -EINVAL;
-		goto out_drop_write;
+		goto out_unlock_inode;
 	}
 
 	if (sbi->options.sys_immutable &&
 	    ((attr | oldattr) & ATTR_SYS) &&
 	    !capable(CAP_LINUX_IMMUTABLE)) {
 		err = -EPERM;
-		goto out_drop_write;
+		goto out_unlock_inode;
 	}
 
 	/*
@@ -90,12 +90,12 @@ static int fat_ioctl_set_attributes(struct file *file, u32 __user *user_attr)
 	 */
 	err = security_inode_setattr(file->f_path.dentry, &ia);
 	if (err)
-		goto out_drop_write;
+		goto out_unlock_inode;
 
 	/* This MUST be done before doing anything irreversible... */
 	err = fat_setattr(file->f_path.dentry, &ia);
 	if (err)
-		goto out_drop_write;
+		goto out_unlock_inode;
 
 	fsnotify_change(file->f_path.dentry, ia.ia_valid);
 	if (sbi->options.sys_immutable) {
@@ -107,10 +107,9 @@ static int fat_ioctl_set_attributes(struct file *file, u32 __user *user_attr)
 
 	fat_save_attrs(inode, attr);
 	mark_inode_dirty(inode);
-out_drop_write:
-	mnt_drop_write_file(file);
 out_unlock_inode:
 	mutex_unlock(&inode->i_mutex);
+	mnt_drop_write_file(file);
 out:
 	return err;
 }
-- 
1.7.1

[PATCH 04/19] btrfs: Push mnt_want_write() outside of i_mutex

[Jan Kara]

When mnt_want_write() starts to handle freezing it will get a full lock
semantics requiring proper lock ordering. So push mnt_want_write() call
consistently outside of i_mutex.

CC: Chris Mason <chris.mason@oracle.com>
CC: linux-btrfs@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/btrfs/ioctl.c |   23 +++++++++++------------
 1 files changed, 11 insertions(+), 12 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 03bb62a..c855e55 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -192,6 +192,10 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 	if (!inode_owner_or_capable(inode))
 		return -EACCES;
 
+	ret = mnt_want_write_file(file);
+	if (ret)
+		return ret;
+
 	mutex_lock(&inode->i_mutex);
 
 	ip_oldflags = ip->flags;
@@ -206,10 +210,6 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 		}
 	}
 
-	ret = mnt_want_write_file(file);
-	if (ret)
-		goto out_unlock;
-
 	if (flags & FS_SYNC_FL)
 		ip->flags |= BTRFS_INODE_SYNC;
 	else
@@ -271,9 +271,9 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
 		inode->i_flags = i_oldflags;
 	}
 
-	mnt_drop_write_file(file);
  out_unlock:
 	mutex_unlock(&inode->i_mutex);
+	mnt_drop_write_file(file);
 	return ret;
 }
 
@@ -624,6 +624,10 @@ static noinline int btrfs_mksubvol(struct path *parent,
 	struct dentry *dentry;
 	int error;
 
+	error = mnt_want_write(parent->mnt);
+	if (error)
+		return error;
+
 	mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
 
 	dentry = lookup_one_len(name, parent->dentry, namelen);
@@ -635,13 +639,9 @@ static noinline int btrfs_mksubvol(struct path *parent,
 	if (dentry->d_inode)
 		goto out_dput;
 
-	error = mnt_want_write(parent->mnt);
-	if (error)
-		goto out_dput;
-
 	error = btrfs_may_create(dir, dentry);
 	if (error)
-		goto out_drop_write;
+		goto out_dput;
 
 	down_read(&BTRFS_I(dir)->root->fs_info->subvol_sem);
 
@@ -659,12 +659,11 @@ static noinline int btrfs_mksubvol(struct path *parent,
 		fsnotify_mkdir(dir, dentry);
 out_up_read:
 	up_read(&BTRFS_I(dir)->root->fs_info->subvol_sem);
-out_drop_write:
-	mnt_drop_write(parent->mnt);
 out_dput:
 	dput(dentry);
 out_unlock:
 	mutex_unlock(&dir->i_mutex);
+	mnt_drop_write(parent->mnt);
 	return error;
 }
 
-- 
1.7.1

[PATCH 05/19] nfsd: Push mnt_want_write() outside of i_mutex

[Jan Kara]

When mnt_want_write() starts to handle freezing it will get a full lock
semantics requiring proper lock ordering. So push mnt_want_write() call
consistently outside of i_mutex.

CC: linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
CC: "J. Bruce Fields" <bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>
Signed-off-by: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
---
 fs/nfsd/nfs4recover.c      |    9 +++--
 fs/nfsd/nfsfh.c            |    1 +
 fs/nfsd/nfsproc.c          |    9 ++++-
 fs/nfsd/vfs.c              |   79 ++++++++++++++++++++++---------------------
 fs/nfsd/vfs.h              |   11 +++++-
 include/linux/nfsd/nfsfh.h |    1 +
 6 files changed, 64 insertions(+), 46 deletions(-)

diff --git a/fs/nfsd/nfs4recover.c b/fs/nfsd/nfs4recover.c
index 0b3e875..8e599a6 100644
--- a/fs/nfsd/nfs4recover.c
+++ b/fs/nfsd/nfs4recover.c
@@ -135,6 +135,10 @@ void nfsd4_create_clid_dir(struct nfs4_client *clp)
 	if (status < 0)
 		return;
 
+	status = mnt_want_write_file(rec_file);
+	if (status)
+		return;
+
 	dir = rec_file->f_path.dentry;
 	/* lock the parent */
 	mutex_lock(&dir->d_inode->i_mutex);
@@ -154,11 +158,7 @@ void nfsd4_create_clid_dir(struct nfs4_client *clp)
 		 * as well be forgiving and just succeed silently.
 		 */
 		goto out_put;
-	status = mnt_want_write_file(rec_file);
-	if (status)
-		goto out_put;
 	status = vfs_mkdir(dir->d_inode, dentry, S_IRWXU);
-	mnt_drop_write_file(rec_file);
 out_put:
 	dput(dentry);
 out_unlock:
@@ -170,6 +170,7 @@ out_unlock:
 				" (err %d); please check that %s exists"
 				" and is writeable", status,
 				user_recovery_dirname);
+	mnt_drop_write_file(rec_file);
 	nfs4_reset_creds(original_cred);
 }
 
diff --git a/fs/nfsd/nfsfh.c b/fs/nfsd/nfsfh.c
index 68454e7..8b93353 100644
--- a/fs/nfsd/nfsfh.c
+++ b/fs/nfsd/nfsfh.c
@@ -635,6 +635,7 @@ fh_put(struct svc_fh *fhp)
 		fhp->fh_post_saved = 0;
 #endif
 	}
+	fh_drop_write(fhp);
 	if (exp) {
 		cache_put(&exp->h, &svc_export_cache);
 		fhp->fh_export = NULL;
diff --git a/fs/nfsd/nfsproc.c b/fs/nfsd/nfsproc.c
index e15dc45..aad6d45 100644
--- a/fs/nfsd/nfsproc.c
+++ b/fs/nfsd/nfsproc.c
@@ -196,6 +196,7 @@ nfsd_proc_create(struct svc_rqst *rqstp, struct nfsd_createargs *argp,
 	struct dentry	*dchild;
 	int		type, mode;
 	__be32		nfserr;
+	int		hosterr;
 	dev_t		rdev = 0, wanted = new_decode_dev(attr->ia_size);
 
 	dprintk("nfsd: CREATE   %s %.*s\n",
@@ -214,6 +215,12 @@ nfsd_proc_create(struct svc_rqst *rqstp, struct nfsd_createargs *argp,
 	nfserr = nfserr_exist;
 	if (isdotent(argp->name, argp->len))
 		goto done;
+	hosterr = fh_want_write(dirfhp);
+	if (hosterr) {
+		nfserr = nfserrno(hosterr);
+		goto done;
+	}
+
 	fh_lock_nested(dirfhp, I_MUTEX_PARENT);
 	dchild = lookup_one_len(argp->name, dirfhp->fh_dentry, argp->len);
 	if (IS_ERR(dchild)) {
@@ -330,7 +337,7 @@ nfsd_proc_create(struct svc_rqst *rqstp, struct nfsd_createargs *argp,
 out_unlock:
 	/* We don't really need to unlock, as fh_put does it. */
 	fh_unlock(dirfhp);
-
+	fh_drop_write(dirfhp);
 done:
 	fh_put(dirfhp);
 	return nfsd_return_dirop(nfserr, resp);
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index edf6d3e..af49c63 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1268,6 +1268,10 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	 * If it has, the parent directory should already be locked.
 	 */
 	if (!resfhp->fh_dentry) {
+		host_err = fh_want_write(fhp);
+		if (host_err)
+			goto out_nfserr;
+
 		/* called from nfsd_proc_mkdir, or possibly nfsd3_proc_create */
 		fh_lock_nested(fhp, I_MUTEX_PARENT);
 		dchild = lookup_one_len(fname, dentry, flen);
@@ -1311,14 +1315,11 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		goto out;
 	}
 
-	host_err = fh_want_write(fhp);
-	if (host_err)
-		goto out_nfserr;
-
 	/*
 	 * Get the dir op function pointer.
 	 */
 	err = 0;
+	host_err = 0;
 	switch (type) {
 	case S_IFREG:
 		host_err = vfs_create(dirp, dchild, iap->ia_mode, NULL);
@@ -1335,10 +1336,8 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		host_err = vfs_mknod(dirp, dchild, iap->ia_mode, rdev);
 		break;
 	}
-	if (host_err < 0) {
-		fh_drop_write(fhp);
+	if (host_err < 0)
 		goto out_nfserr;
-	}
 
 	err = nfsd_create_setattr(rqstp, resfhp, iap);
 
@@ -1350,7 +1349,6 @@ nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	err2 = nfserrno(commit_metadata(fhp));
 	if (err2)
 		err = err2;
-	fh_drop_write(fhp);
 	/*
 	 * Update the file handle to get the new inode info.
 	 */
@@ -1409,6 +1407,11 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	err = nfserr_notdir;
 	if (!dirp->i_op->lookup)
 		goto out;
+
+	host_err = fh_want_write(fhp);
+	if (host_err)
+		goto out_nfserr;
+
 	fh_lock_nested(fhp, I_MUTEX_PARENT);
 
 	/*
@@ -1441,9 +1444,6 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 		v_atime = verifier[1]&0x7fffffff;
 	}
 	
-	host_err = fh_want_write(fhp);
-	if (host_err)
-		goto out_nfserr;
 	if (dchild->d_inode) {
 		err = 0;
 
@@ -1514,7 +1514,6 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (!err)
 		err = nfserrno(commit_metadata(fhp));
 
-	fh_drop_write(fhp);
 	/*
 	 * Update the filehandle to get the new inode info.
 	 */
@@ -1525,6 +1524,7 @@ do_nfsd_create(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	fh_unlock(fhp);
 	if (dchild && !IS_ERR(dchild))
 		dput(dchild);
+	fh_drop_write(fhp);
  	return err;
  
  out_nfserr:
@@ -1604,6 +1604,11 @@ nfsd_symlink(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	err = fh_verify(rqstp, fhp, S_IFDIR, NFSD_MAY_CREATE);
 	if (err)
 		goto out;
+
+	host_err = fh_want_write(fhp);
+	if (host_err)
+		goto out_nfserr;
+
 	fh_lock(fhp);
 	dentry = fhp->fh_dentry;
 	dnew = lookup_one_len(fname, dentry, flen);
@@ -1611,10 +1616,6 @@ nfsd_symlink(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (IS_ERR(dnew))
 		goto out_nfserr;
 
-	host_err = fh_want_write(fhp);
-	if (host_err)
-		goto out_nfserr;
-
 	if (unlikely(path[plen] != 0)) {
 		char *path_alloced = kmalloc(plen+1, GFP_KERNEL);
 		if (path_alloced == NULL)
@@ -1674,6 +1675,12 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
 	if (isdotent(name, len))
 		goto out;
 
+	host_err = fh_want_write(tfhp);
+	if (host_err) {
+		err = nfserrno(host_err);
+		goto out;
+	}
+
 	fh_lock_nested(ffhp, I_MUTEX_PARENT);
 	ddir = ffhp->fh_dentry;
 	dirp = ddir->d_inode;
@@ -1685,18 +1692,13 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
 
 	dold = tfhp->fh_dentry;
 
-	host_err = fh_want_write(tfhp);
-	if (host_err) {
-		err = nfserrno(host_err);
-		goto out_dput;
-	}
 	err = nfserr_noent;
 	if (!dold->d_inode)
-		goto out_drop_write;
+		goto out_dput;
 	host_err = nfsd_break_lease(dold->d_inode);
 	if (host_err) {
 		err = nfserrno(host_err);
-		goto out_drop_write;
+		goto out_dput;
 	}
 	host_err = vfs_link(dold, dirp, dnew);
 	if (!host_err) {
@@ -1709,12 +1711,11 @@ nfsd_link(struct svc_rqst *rqstp, struct svc_fh *ffhp,
 		else
 			err = nfserrno(host_err);
 	}
-out_drop_write:
-	fh_drop_write(tfhp);
 out_dput:
 	dput(dnew);
 out_unlock:
 	fh_unlock(ffhp);
+	fh_drop_write(tfhp);
 out:
 	return err;
 
@@ -1757,6 +1758,12 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
 	if (!flen || isdotent(fname, flen) || !tlen || isdotent(tname, tlen))
 		goto out;
 
+	host_err = fh_want_write(ffhp);
+	if (host_err) {
+		err = nfserrno(host_err);
+		goto out;
+	}
+
 	/* cannot use fh_lock as we need deadlock protective ordering
 	 * so do it by hand */
 	trap = lock_rename(tdentry, fdentry);
@@ -1787,17 +1794,14 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
 	host_err = -EXDEV;
 	if (ffhp->fh_export->ex_path.mnt != tfhp->fh_export->ex_path.mnt)
 		goto out_dput_new;
-	host_err = fh_want_write(ffhp);
-	if (host_err)
-		goto out_dput_new;
 
 	host_err = nfsd_break_lease(odentry->d_inode);
 	if (host_err)
-		goto out_drop_write;
+		goto out_dput_new;
 	if (ndentry->d_inode) {
 		host_err = nfsd_break_lease(ndentry->d_inode);
 		if (host_err)
-			goto out_drop_write;
+			goto out_dput_new;
 	}
 	host_err = vfs_rename(fdir, odentry, tdir, ndentry);
 	if (!host_err) {
@@ -1805,8 +1809,6 @@ nfsd_rename(struct svc_rqst *rqstp, struct svc_fh *ffhp, char *fname, int flen,
 		if (!host_err)
 			host_err = commit_metadata(ffhp);
 	}
-out_drop_write:
-	fh_drop_write(ffhp);
  out_dput_new:
 	dput(ndentry);
  out_dput_old:
@@ -1822,6 +1824,7 @@ out_drop_write:
 	fill_post_wcc(tfhp);
 	unlock_rename(tdentry, fdentry);
 	ffhp->fh_locked = tfhp->fh_locked = 0;
+	fh_drop_write(ffhp);
 
 out:
 	return err;
@@ -1847,6 +1850,10 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
 	if (err)
 		goto out;
 
+	host_err = fh_want_write(fhp);
+	if (host_err)
+		goto out_nfserr;
+
 	fh_lock_nested(fhp, I_MUTEX_PARENT);
 	dentry = fhp->fh_dentry;
 	dirp = dentry->d_inode;
@@ -1865,21 +1872,15 @@ nfsd_unlink(struct svc_rqst *rqstp, struct svc_fh *fhp, int type,
 	if (!type)
 		type = rdentry->d_inode->i_mode & S_IFMT;
 
-	host_err = fh_want_write(fhp);
-	if (host_err)
-		goto out_put;
-
 	host_err = nfsd_break_lease(rdentry->d_inode);
 	if (host_err)
-		goto out_drop_write;
+		goto out_put;
 	if (type != S_IFDIR)
 		host_err = vfs_unlink(dirp, rdentry);
 	else
 		host_err = vfs_rmdir(dirp, rdentry);
 	if (!host_err)
 		host_err = commit_metadata(fhp);
-out_drop_write:
-	fh_drop_write(fhp);
 out_put:
 	dput(rdentry);
 
diff --git a/fs/nfsd/vfs.h b/fs/nfsd/vfs.h
index 1dcd238..d5a50b4 100644
--- a/fs/nfsd/vfs.h
+++ b/fs/nfsd/vfs.h
@@ -108,12 +108,19 @@ int nfsd_set_posix_acl(struct svc_fh *, int, struct posix_acl *);
 
 static inline int fh_want_write(struct svc_fh *fh)
 {
-	return mnt_want_write(fh->fh_export->ex_path.mnt);
+	int ret = mnt_want_write(fh->fh_export->ex_path.mnt);
+
+	if (!ret)
+		fh->fh_want_write = 1;
+	return ret;
 }
 
 static inline void fh_drop_write(struct svc_fh *fh)
 {
-	mnt_drop_write(fh->fh_export->ex_path.mnt);
+	if (fh->fh_want_write) {
+		fh->fh_want_write = 0;
+		mnt_drop_write(fh->fh_export->ex_path.mnt);
+	}
 }
 
 #endif /* LINUX_NFSD_VFS_H */
diff --git a/include/linux/nfsd/nfsfh.h b/include/linux/nfsd/nfsfh.h
index ce4743a..fa63048 100644
--- a/include/linux/nfsd/nfsfh.h
+++ b/include/linux/nfsd/nfsfh.h
@@ -143,6 +143,7 @@ typedef struct svc_fh {
 	int			fh_maxsize;	/* max size for fh_handle */
 
 	unsigned char		fh_locked;	/* inode locked by us */
+	unsigned char		fh_want_write;	/* remount protection taken */
 
 #ifdef CONFIG_NFSD_V3
 	unsigned char		fh_post_saved;	/* post-op attrs saved */
-- 
1.7.1

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[PATCH 06/19] fs: Improve filesystem freezing handling

[Jan Kara]

vfs_check_frozen() tests are racy since the filesystem can be frozen just after
the test is performed. Thus in write paths we can end up marking some pages or
inodes dirty even though the file system is already frozen. This creates
problems with flusher thread hanging on frozen filesystem.

Another problem is that exclusion between ->page_mkwrite() and filesystem
freezing has been handled by setting page dirty and then verifying s_frozen.
This guaranteed that either the freezing code sees the faulted page, writes it,
and writeprotects it again or we see s_frozen set and bail out of page fault.
This works to protect from page being marked writeable while filesystem
freezing is running but has an unpleasant artefact of leaving dirty (although
unmodified and writeprotected) pages on frozen filesystem resulting in similar
problems with flusher thread as the first problem.

This patch aims at providing exclusion between write paths and filesystem
freezing. We implement a writer-freeze read-write semaphore in the superblock.
Actually, there are three such semaphores because of lock ranking reasons - one
for page fault handlers (->page_mkwrite), one for all other writers, and one of
internal filesystem purposes (used e.g. to track running transactions).  Write
paths which should block freezing (e.g. directory operations, ->aio_write(),
->page_mkwrite) hold reader side of the semaphore. Code freezing the filesystem
takes the writer side.

Only that we don't really want to bounce cachelines of the semaphores between
CPUs for each write happening. So we implement the reader side of the semaphore
as a per-cpu counter and the writer side is implemented using s_writers.frozen
superblock field.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/super.c         |  304 ++++++++++++++++++++++++++++++++++++++++++++++++----
 include/linux/fs.h |   48 +++++++--
 2 files changed, 323 insertions(+), 29 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 6277ec6..9203907 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -32,12 +32,20 @@
 #include <linux/backing-dev.h>
 #include <linux/rculist_bl.h>
 #include <linux/cleancache.h>
+#include <linux/lockdep.h>
 #include "internal.h"
 
 
 LIST_HEAD(super_blocks);
 DEFINE_SPINLOCK(sb_lock);
 
+static struct lock_class_key sb_writers_key[SB_FREEZE_LEVELS];
+static char *sb_writers_name[SB_FREEZE_LEVELS] = {
+	"sb_writers",
+	"sb_pagefaults",
+	"sb_internal",
+};
+
 /*
  * One thing we have to be careful of with a per-sb shrinker is that we don't
  * drop the last active reference to the superblock from within the shrinker.
@@ -101,6 +109,35 @@ static int prune_super(struct shrinker *shrink, struct shrink_control *sc)
 	return total_objects;
 }
 
+static int init_sb_writers(struct super_block *s)
+{
+	int err;
+	int i;
+
+	for (i = 0; i < SB_FREEZE_LEVELS; i++) {
+		err = percpu_counter_init(&s->s_writers.counter[i], 0);
+		if (err < 0)
+			goto err_out;
+		lockdep_init_map(&s->s_writers.lock_map[i], sb_writers_name[i],
+				 &sb_writers_key[i], 0);
+	}
+	init_waitqueue_head(&s->s_writers.wait);
+	init_waitqueue_head(&s->s_writers.wait_unfrozen);
+	return 0;
+err_out:
+	while (--i >= 0)
+		percpu_counter_destroy(&s->s_writers.counter[i]);
+	return err;
+}
+
+static void destroy_sb_writers(struct super_block *s)
+{
+	int i;
+
+	for (i = 0; i < SB_FREEZE_LEVELS; i++)
+		percpu_counter_destroy(&s->s_writers.counter[i]);
+}
+
 /**
  *	alloc_super	-	create new superblock
  *	@type:	filesystem type superblock should belong to
@@ -115,18 +152,19 @@ static struct super_block *alloc_super(struct file_system_type *type)
 
 	if (s) {
 		if (security_sb_alloc(s)) {
+			/*
+			 * We cannot call security_sb_free() without
+			 * security_sb_alloc() succeeding. So bail out manually
+			 */
 			kfree(s);
 			s = NULL;
 			goto out;
 		}
 #ifdef CONFIG_SMP
 		s->s_files = alloc_percpu(struct list_head);
-		if (!s->s_files) {
-			security_sb_free(s);
-			kfree(s);
-			s = NULL;
-			goto out;
-		} else {
+		if (!s->s_files)
+			goto err_out;
+		else {
 			int i;
 
 			for_each_possible_cpu(i)
@@ -135,6 +173,9 @@ static struct super_block *alloc_super(struct file_system_type *type)
 #else
 		INIT_LIST_HEAD(&s->s_files);
 #endif
+		if (init_sb_writers(s))
+			goto err_out;
+
 		s->s_bdi = &default_backing_dev_info;
 		INIT_HLIST_NODE(&s->s_instances);
 		INIT_HLIST_BL_HEAD(&s->s_anon);
@@ -187,6 +228,16 @@ static struct super_block *alloc_super(struct file_system_type *type)
 	}
 out:
 	return s;
+err_out:
+	security_sb_free(s);
+#ifdef CONFIG_SMP
+	if (s->s_files)
+		free_percpu(s->s_files);
+#endif
+	destroy_sb_writers(s);
+	kfree(s);
+	s = NULL;
+	goto out;
 }
 
 /**
@@ -200,6 +251,7 @@ static inline void destroy_super(struct super_block *s)
 #ifdef CONFIG_SMP
 	free_percpu(s->s_files);
 #endif
+	destroy_sb_writers(s);
 	security_sb_free(s);
 	WARN_ON(!list_empty(&s->s_mounts));
 	kfree(s->s_subtype);
@@ -646,10 +698,11 @@ struct super_block *get_super_thawed(struct block_device *bdev)
 {
 	while (1) {
 		struct super_block *s = get_super(bdev);
-		if (!s || s->s_frozen == SB_UNFROZEN)
+		if (!s || s->s_writers.frozen == SB_UNFROZEN)
 			return s;
 		up_read(&s->s_umount);
-		vfs_check_frozen(s, SB_FREEZE_WRITE);
+		wait_event(s->s_writers.wait_unfrozen,
+			   s->s_writers.frozen == SB_UNFROZEN);
 		put_super(s);
 	}
 }
@@ -727,7 +780,7 @@ int do_remount_sb(struct super_block *sb, int flags, void *data, int force)
 	int retval;
 	int remount_ro;
 
-	if (sb->s_frozen != SB_UNFROZEN)
+	if (sb->s_writers.frozen != SB_UNFROZEN)
 		return -EBUSY;
 
 #ifdef CONFIG_BLOCK
@@ -1162,6 +1215,196 @@ out:
 	return ERR_PTR(error);
 }
 
+static void __sb_end_write(struct super_block *sb, int level)
+{
+	percpu_counter_dec(&sb->s_writers.counter[level-1]);
+	/*
+	 * Make sure s_writers are updated before we wake up waiters in
+	 * freeze_super().
+	 */
+	smp_mb();
+	if (waitqueue_active(&sb->s_writers.wait))
+		wake_up(&sb->s_writers.wait);
+	rwsem_release(&sb->s_writers.lock_map[level-1], 1, _RET_IP_);
+}
+
+/**
+ * sb_end_write - drop write access to a superblock
+ * @sb: the super we wrote to
+ *
+ * Decrement number of writers to the filesystem. Wake up possible waiters
+ * wanting to freeze the filesystem.
+ */
+void sb_end_write(struct super_block *sb)
+{
+	__sb_end_write(sb, SB_FREEZE_WRITE);
+}
+EXPORT_SYMBOL(sb_end_write);
+
+/**
+ * sb_end_pagefault - drop write access to a superblock from a page fault
+ * @sb: the super we wrote to
+ *
+ * Decrement number of processes handling write page fault to the filesystem.
+ * Wake up possible waiters wanting to freeze the filesystem.
+ */
+void sb_end_pagefault(struct super_block *sb)
+{
+	__sb_end_write(sb, SB_FREEZE_PAGEFAULT);
+}
+EXPORT_SYMBOL(sb_end_pagefault);
+
+/**
+ * sb_end_intwrite - drop write access to a superblock for internal fs purposes
+ * @sb: the super we wrote to
+ *
+ * Decrement fs-internal number of writers to the filesystem.  Wake up possible
+ * waiters wanting to freeze the filesystem.
+ */
+void sb_end_intwrite(struct super_block *sb)
+{
+	__sb_end_write(sb, SB_FREEZE_FS);
+}
+EXPORT_SYMBOL(sb_end_intwrite);
+
+static int __sb_start_write(struct super_block *sb, int level, bool wait)
+{
+retry:
+	if (wait) {
+		wait_event(sb->s_writers.wait_unfrozen,
+			   sb->s_writers.frozen < level);
+	} else if (sb->s_writers.frozen >= level)
+		return 0;
+
+	rwsem_acquire_read(&sb->s_writers.lock_map[level-1], 0, !wait,
+			   _RET_IP_);
+	percpu_counter_inc(&sb->s_writers.counter[level-1]);
+	/*
+	 * Make sure counter is updated before we check for frozen.
+	 * freeze_super() first sets frozen and then checks the counter.
+	 */
+	smp_mb();
+	if (sb->s_writers.frozen >= level) {
+		__sb_end_write(sb, level);
+		goto retry;
+	}
+	return 1;
+}
+
+/**
+ * sb_start_write - get write access to a superblock
+ * @sb: the super we write to
+ *
+ * When a process wants to write data or metadata to a file system (i.e. dirty
+ * a page or an inode), it should embed the operation in a sb_start_write() -
+ * sb_end_write() pair to get exclusion against file system freezing. This
+ * function increments number of writers preventing freezing. If the file
+ * system is already frozen, the function waits until the file system is
+ * thawed.
+ *
+ * Since freeze protection behaves as a lock, users have to preserve
+ * ordering of freeze protection and other filesystem locks. Generally,
+ * freeze protection should be the outermost lock. In particular, we have:
+ *
+ * sb_start_write
+ *   -> i_mutex			(write path, truncate, directory ops, ...)
+ *   -> s_umount		(freeze_super, thaw_super)
+ */
+void sb_start_write(struct super_block *sb)
+{
+	__sb_start_write(sb, SB_FREEZE_WRITE, true);
+}
+EXPORT_SYMBOL(sb_start_write);
+
+int sb_start_write_trylock(struct super_block *sb)
+{
+	return __sb_start_write(sb, SB_FREEZE_WRITE, false);
+}
+EXPORT_SYMBOL(sb_start_write_trylock);
+
+/**
+ * sb_start_pagefault - get write access to a superblock from a page fault
+ * @sb: the super we write to
+ *
+ * When a process starts handling write page fault, it should embed the
+ * operation into sb_start_pagefault() - sb_end_pagefault() pair to get
+ * exclusion against file system freezing. This is needed since the page fault
+ * is going to dirty a page. This function increments number of running page
+ * faults preventing freezing. If the file system is already frozen, the
+ * function waits until the file system is thawed.
+ *
+ * Since page fault freeze protection behaves as a lock, users have to preserve
+ * ordering of freeze protection and other filesystem locks. It is advised to
+ * put sb_start_pagefault() close to mmap_sem in lock ordering. Page fault
+ * handling code implies lock dependency:
+ *
+ * mmap_sem
+ *   -> sb_start_pagefault
+ */
+void sb_start_pagefault(struct super_block *sb)
+{
+	__sb_start_write(sb, SB_FREEZE_PAGEFAULT, true);
+}
+EXPORT_SYMBOL(sb_start_pagefault);
+
+/*
+ * sb_start_intwrite - get write access to a superblock for internal fs purposes
+ * @sb: the super we write to
+ *
+ * This is the third level of protection against filesystem freezing. It is
+ * free for use by a filesystem. The only requirement is that it must rank
+ * below sb_start_pagefault.
+ *
+ * For example filesystem can call sb_start_intwrite() when starting a
+ * transaction which somewhat eases handling of freezing for internal sources
+ * of filesystem changes (internal fs threads, discarding preallocation on file
+ * close, etc.).
+ */
+void sb_start_intwrite(struct super_block *sb)
+{
+	__sb_start_write(sb, SB_FREEZE_FS, true);
+}
+EXPORT_SYMBOL(sb_start_intwrite);
+
+/**
+ * sb_wait_write - wait until all writers to given file system finish
+ * @sb: the super for which we wait
+ * @level: type of writers we wait for (normal vs page fault)
+ *
+ * This function waits until there are no writers of given type to given file
+ * system. Caller of this function should make sure there can be no new writers
+ * of type @level before calling this function. Otherwise this function can
+ * livelock.
+ */
+static void sb_wait_write(struct super_block *sb, int level)
+{
+	s64 writers;
+
+	/*
+	 * We just cycle-through lockdep here so that it does not complain
+	 * about returning with lock to userspace
+	 */
+	rwsem_acquire(&sb->s_writers.lock_map[level-1], 0, 0, _THIS_IP_);
+	rwsem_release(&sb->s_writers.lock_map[level-1], 1, _THIS_IP_);
+
+	do {
+		DEFINE_WAIT(wait);
+
+		/*
+		 * We use a barrier in prepare_to_wait() to separate setting
+		 * of frozen and checking of the counter
+		 */
+		prepare_to_wait(&sb->s_writers.wait, &wait,
+				TASK_UNINTERRUPTIBLE);
+
+		writers = percpu_counter_sum(&sb->s_writers.counter[level-1]);
+		if (writers)
+			schedule();
+
+		finish_wait(&sb->s_writers.wait, &wait);
+	} while (writers);
+}
+
 /**
  * freeze_super - lock the filesystem and force it into a consistent state
  * @sb: the super to lock
@@ -1176,7 +1419,7 @@ int freeze_super(struct super_block *sb)
 
 	atomic_inc(&sb->s_active);
 	down_write(&sb->s_umount);
-	if (sb->s_frozen) {
+	if (sb->s_writers.frozen != SB_UNFROZEN) {
 		deactivate_locked_super(sb);
 		return -EBUSY;
 	}
@@ -1187,33 +1430,53 @@ int freeze_super(struct super_block *sb)
 	}
 
 	if (sb->s_flags & MS_RDONLY) {
-		sb->s_frozen = SB_FREEZE_TRANS;
-		smp_wmb();
+		/* Nothing to do really... */
+		sb->s_writers.frozen = SB_FREEZE_COMPLETE;
 		up_write(&sb->s_umount);
 		return 0;
 	}
 
-	sb->s_frozen = SB_FREEZE_WRITE;
+	/* From now on, no new normal writers can start */
+	sb->s_writers.frozen = SB_FREEZE_WRITE;
 	smp_wmb();
 
+	/* Release s_umount to preserve sb_start_write -> s_umount ordering */
+	up_write(&sb->s_umount);
+
+	sb_wait_write(sb, SB_FREEZE_WRITE);
+
+	/* Now we go and block page faults... */
+	down_write(&sb->s_umount);
+	sb->s_writers.frozen = SB_FREEZE_PAGEFAULT;
+	smp_wmb();
+
+	sb_wait_write(sb, SB_FREEZE_PAGEFAULT);
+
+	/* All writers are done so after syncing there won't be dirty data */
 	sync_filesystem(sb);
 
-	sb->s_frozen = SB_FREEZE_TRANS;
+	/* Now wait for internal filesystem counter */
+	sb->s_writers.frozen = SB_FREEZE_FS;
 	smp_wmb();
+	sb_wait_write(sb, SB_FREEZE_FS);
 
-	sync_blockdev(sb->s_bdev);
 	if (sb->s_op->freeze_fs) {
 		ret = sb->s_op->freeze_fs(sb);
 		if (ret) {
 			printk(KERN_ERR
 				"VFS:Filesystem freeze failed\n");
-			sb->s_frozen = SB_UNFROZEN;
+			sb->s_writers.frozen = SB_UNFROZEN;
 			smp_wmb();
-			wake_up(&sb->s_wait_unfrozen);
+			wake_up(&sb->s_writers.wait_unfrozen);
 			deactivate_locked_super(sb);
 			return ret;
 		}
 	}
+	/*
+	 * This is just for debugging purposes so that fs can warn if it
+	 * sees write activity when frozen is set to SB_FREEZE_COMPLETE.
+	 */
+	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
 	up_write(&sb->s_umount);
 	return 0;
 }
@@ -1230,7 +1493,7 @@ int thaw_super(struct super_block *sb)
 	int error;
 
 	down_write(&sb->s_umount);
-	if (sb->s_frozen == SB_UNFROZEN) {
+	if (sb->s_writers.frozen == SB_UNFROZEN) {
 		up_write(&sb->s_umount);
 		return -EINVAL;
 	}
@@ -1243,16 +1506,15 @@ int thaw_super(struct super_block *sb)
 		if (error) {
 			printk(KERN_ERR
 				"VFS:Filesystem thaw failed\n");
-			sb->s_frozen = SB_FREEZE_TRANS;
 			up_write(&sb->s_umount);
 			return error;
 		}
 	}
 
 out:
-	sb->s_frozen = SB_UNFROZEN;
+	sb->s_writers.frozen = SB_UNFROZEN;
 	smp_wmb();
-	wake_up(&sb->s_wait_unfrozen);
+	wake_up(&sb->s_writers.wait_unfrozen);
 	deactivate_locked_super(sb);
 
 	return 0;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 69cd5bb..2c7c7bf 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -397,6 +397,7 @@ struct inodes_stat_t {
 #include <linux/atomic.h>
 #include <linux/shrinker.h>
 #include <linux/migrate_mode.h>
+#include <linux/lockdep.h>
 
 #include <asm/byteorder.h>
 
@@ -1392,6 +1393,16 @@ extern void f_delown(struct file *filp);
 extern pid_t f_getown(struct file *filp);
 extern int send_sigurg(struct fown_struct *fown);
 
+struct mm_struct;
+
+void sb_start_write(struct super_block *sb);
+int sb_start_write_trylock(struct super_block *sb);
+void sb_end_write(struct super_block *sb);
+void sb_start_pagefault(struct super_block *sb);
+void sb_end_pagefault(struct super_block *sb);
+void sb_start_intwrite(struct super_block *sb);
+void sb_end_intwrite(struct super_block *sb);
+
 /*
  *	Umount options
  */
@@ -1405,6 +1416,32 @@ extern int send_sigurg(struct fown_struct *fown);
 extern struct list_head super_blocks;
 extern spinlock_t sb_lock;
 
+/* Possible states of 'frozen' field */
+enum {
+	SB_UNFROZEN = 0,		/* FS is unfrozen */
+	SB_FREEZE_WRITE	= 1,		/* Writes, dir ops, ioctls frozen */
+	SB_FREEZE_TRANS = 2,
+	SB_FREEZE_PAGEFAULT = 2,	/* Page faults stopped as well */
+	SB_FREEZE_FS = 3,		/* For internal FS use (e.g. to stop
+					 * internal threads if needed) */
+	SB_FREEZE_COMPLETE = 4,		/* ->freeze_fs finished successfully */
+};
+
+#define SB_FREEZE_LEVELS (SB_FREEZE_COMPLETE - 1)
+
+struct sb_writers {
+	/* Counters for counting writers at each level */
+	struct percpu_counter	counter[SB_FREEZE_LEVELS];
+	wait_queue_head_t	wait;		/* queue for waiting for
+						   writers / faults to finish */
+	int			frozen;		/* Is sb frozen? */
+	wait_queue_head_t	wait_unfrozen;	/* queue for waiting for
+						   sb to be thawed */
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	struct lockdep_map	lock_map[SB_FREEZE_LEVELS];
+#endif
+};
+
 struct super_block {
 	struct list_head	s_list;		/* Keep this first */
 	dev_t			s_dev;		/* search index; _not_ kdev_t */
@@ -1454,6 +1491,7 @@ struct super_block {
 
 	int			s_frozen;
 	wait_queue_head_t	s_wait_unfrozen;
+	struct sb_writers	s_writers;
 
 	char s_id[32];				/* Informational name */
 	u8 s_uuid[16];				/* UUID */
@@ -1507,14 +1545,8 @@ extern struct timespec current_fs_time(struct super_block *sb);
 /*
  * Snapshotting support.
  */
-enum {
-	SB_UNFROZEN = 0,
-	SB_FREEZE_WRITE	= 1,
-	SB_FREEZE_TRANS = 2,
-};
-
-#define vfs_check_frozen(sb, level) \
-	wait_event((sb)->s_wait_unfrozen, ((sb)->s_frozen < (level)))
+/* Will go away when all users are converted */
+#define vfs_check_frozen(sb, level) do { } while (0)
 
 /*
  * until VFS tracks user namespaces for inodes, just make all files
-- 
1.7.1

[PATCH 07/19] fs: Add freezing handling to mnt_want_write() / mnt_drop_write()

[Jan Kara]

Most of places where we want freeze protection coincides with the places where
we also have remount-ro protection. So make mnt_want_write() and
mnt_drop_write() (and their _file alternative) prevent freezing as well.
For the few cases that are really interested only in remount-ro protection
provide new function variants.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/file_table.c       |    2 +-
 fs/inode.c            |    4 +-
 fs/namei.c            |   16 +++++++-
 fs/namespace.c        |  101 +++++++++++++++++++++++++++++++++++++++----------
 fs/open.c             |    2 +-
 include/linux/mount.h |    4 ++
 6 files changed, 103 insertions(+), 26 deletions(-)

diff --git a/fs/file_table.c b/fs/file_table.c
index 20002e3..31ab06f 100644
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -216,7 +216,7 @@ void drop_file_write_access(struct file *file)
 		return;
 	if (file_check_writeable(file) != 0)
 		return;
-	mnt_drop_write(mnt);
+	__mnt_drop_write(mnt);
 	file_release_write(file);
 }
 EXPORT_SYMBOL_GPL(drop_file_write_access);
diff --git a/fs/inode.c b/fs/inode.c
index d3ebdbe..095828c 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1580,7 +1580,7 @@ void file_update_time(struct file *file)
 		return;
 
 	/* Finally allowed to write? Takes lock. */
-	if (mnt_want_write_file(file))
+	if (__mnt_want_write_file(file))
 		return;
 
 	/* Only change inode inside the lock region */
@@ -1591,7 +1591,7 @@ void file_update_time(struct file *file)
 	if (sync_it & S_MTIME)
 		inode->i_mtime = now;
 	mark_inode_dirty_sync(inode);
-	mnt_drop_write_file(file);
+	__mnt_drop_write_file(file);
 }
 EXPORT_SYMBOL(file_update_time);
 
diff --git a/fs/namei.c b/fs/namei.c
index 575d3a4..474b6b2 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2166,12 +2166,21 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 	if (nd->last.name[nd->last.len])
 		goto exit;
 
+	/*
+	 * We don't know whether write access will be needed or not. But we
+	 * must get the protection before getting i_mutex due to locking
+	 * constraints. Thus O_CREAT open will get blocked on frozen filesystem
+	 * even if it didn't need to create anything. Not that surprising...
+	 */
+	sb_start_write(dir->d_sb);
+
 	mutex_lock(&dir->d_inode->i_mutex);
 
 	dentry = lookup_hash(nd);
 	error = PTR_ERR(dentry);
 	if (IS_ERR(dentry)) {
 		mutex_unlock(&dir->d_inode->i_mutex);
+		sb_end_write(dir->d_sb);
 		goto exit;
 	}
 
@@ -2190,9 +2199,11 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 		 * a permanent write count is taken through
 		 * the 'struct file' in nameidata_to_filp().
 		 */
-		error = mnt_want_write(nd->path.mnt);
-		if (error)
+		error = __mnt_want_write(nd->path.mnt);
+		if (error) {
+			sb_end_write(dir->d_sb);
 			goto exit_mutex_unlock;
+		}
 		want_write = 1;
 		/* Don't check for write permission, don't truncate */
 		open_flag &= ~O_TRUNC;
@@ -2214,6 +2225,7 @@ static struct file *do_last(struct nameidata *nd, struct path *path,
 	 * It already exists.
 	 */
 	mutex_unlock(&dir->d_inode->i_mutex);
+	sb_end_write(dir->d_sb);
 	audit_inode(pathname, path->dentry);
 
 	error = -EEXIST;
diff --git a/fs/namespace.c b/fs/namespace.c
index e608199..157afbe 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -283,24 +283,22 @@ static int mnt_is_readonly(struct vfsmount *mnt)
 }
 
 /*
- * Most r/o checks on a fs are for operations that take
- * discrete amounts of time, like a write() or unlink().
- * We must keep track of when those operations start
- * (for permission checks) and when they end, so that
- * we can determine when writes are able to occur to
- * a filesystem.
+ * Most r/o & frozen checks on a fs are for operations that take discrete
+ * amounts of time, like a write() or unlink().  We must keep track of when
+ * those operations start (for permission checks) and when they end, so that we
+ * can determine when writes are able to occur to a filesystem.
  */
 /**
- * mnt_want_write - get write access to a mount
+ * __mnt_want_write - get write access to a mount without freeze protection
  * @m: the mount on which to take a write
  *
- * This tells the low-level filesystem that a write is
- * about to be performed to it, and makes sure that
- * writes are allowed before returning success.  When
- * the write operation is finished, mnt_drop_write()
- * must be called.  This is effectively a refcount.
+ * This tells the low-level filesystem that a write is about to be performed to
+ * it, and makes sure that writes are allowed (mnt it read-write) before
+ * returning success. This operation does not protect against filesystem being
+ * frozen. When the write operation is finished, __mnt_drop_write() must be
+ * called. This is effectively a refcount.
  */
-int mnt_want_write(struct vfsmount *m)
+int __mnt_want_write(struct vfsmount *m)
 {
 	struct mount *mnt = real_mount(m);
 	int ret = 0;
@@ -326,6 +324,28 @@ int mnt_want_write(struct vfsmount *m)
 		ret = -EROFS;
 	}
 	preempt_enable();
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(__mnt_want_write);
+
+/**
+ * mnt_want_write - get write access to a mount
+ * @m: the mount on which to take a write
+ *
+ * This tells the low-level filesystem that a write is about to be performed to
+ * it, and makes sure that writes are allowed (mount is read-write, filesystem
+ * is not frozen) before returning success.  When the write operation is
+ * finished, mnt_drop_write() must be called.  This is effectively a refcount.
+ */
+int mnt_want_write(struct vfsmount *m)
+{
+	int ret;
+
+	sb_start_write(m->mnt_sb);
+	ret = __mnt_want_write(m);
+	if (ret)
+		sb_end_write(m->mnt_sb);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(mnt_want_write);
@@ -355,38 +375,79 @@ int mnt_clone_write(struct vfsmount *mnt)
 EXPORT_SYMBOL_GPL(mnt_clone_write);
 
 /**
- * mnt_want_write_file - get write access to a file's mount
+ * __mnt_want_write_file - get write access to a file's mount
  * @file: the file who's mount on which to take a write
  *
- * This is like mnt_want_write, but it takes a file and can
+ * This is like __mnt_want_write, but it takes a file and can
  * do some optimisations if the file is open for write already
  */
-int mnt_want_write_file(struct file *file)
+int __mnt_want_write_file(struct file *file)
 {
 	struct inode *inode = file->f_dentry->d_inode;
+
 	if (!(file->f_mode & FMODE_WRITE) || special_file(inode->i_mode))
-		return mnt_want_write(file->f_path.mnt);
+		return __mnt_want_write(file->f_path.mnt);
 	else
 		return mnt_clone_write(file->f_path.mnt);
 }
+EXPORT_SYMBOL_GPL(__mnt_want_write_file);
+
+/**
+ * mnt_want_write_file - get write access to a file's mount
+ * @file: the file who's mount on which to take a write
+ *
+ * This is like mnt_want_write, but it takes a file and can
+ * do some optimisations if the file is open for write already
+ */
+int mnt_want_write_file(struct file *file)
+{
+	int ret;
+
+	sb_start_write(file->f_path.mnt->mnt_sb);
+	ret = __mnt_want_write_file(file);
+	if (ret)
+		sb_end_write(file->f_path.mnt->mnt_sb);
+	return ret;
+}
 EXPORT_SYMBOL_GPL(mnt_want_write_file);
 
 /**
- * mnt_drop_write - give up write access to a mount
+ * __mnt_drop_write - give up write access to a mount
  * @mnt: the mount on which to give up write access
  *
  * Tells the low-level filesystem that we are done
  * performing writes to it.  Must be matched with
- * mnt_want_write() call above.
+ * __mnt_want_write() call above.
  */
-void mnt_drop_write(struct vfsmount *mnt)
+void __mnt_drop_write(struct vfsmount *mnt)
 {
 	preempt_disable();
 	mnt_dec_writers(real_mount(mnt));
 	preempt_enable();
 }
+EXPORT_SYMBOL_GPL(__mnt_drop_write);
+
+/**
+ * mnt_drop_write - give up write access to a mount
+ * @mnt: the mount on which to give up write access
+ *
+ * Tells the low-level filesystem that we are done performing writes to it and
+ * also allows filesystem to be frozen again.  Must be matched with
+ * mnt_want_write() call above.
+ */
+void mnt_drop_write(struct vfsmount *mnt)
+{
+	__mnt_drop_write(mnt);
+	sb_end_write(mnt->mnt_sb);
+}
 EXPORT_SYMBOL_GPL(mnt_drop_write);
 
+void __mnt_drop_write_file(struct file *file)
+{
+	__mnt_drop_write(file->f_path.mnt);
+}
+EXPORT_SYMBOL(__mnt_drop_write_file);
+
 void mnt_drop_write_file(struct file *file)
 {
 	mnt_drop_write(file->f_path.mnt);
diff --git a/fs/open.c b/fs/open.c
index 77becc0..456e415 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -637,7 +637,7 @@ static inline int __get_file_write_access(struct inode *inode,
 		/*
 		 * Balanced in __fput()
 		 */
-		error = mnt_want_write(mnt);
+		error = __mnt_want_write(mnt);
 		if (error)
 			put_write_access(inode);
 	}
diff --git a/include/linux/mount.h b/include/linux/mount.h
index d7029f4..d6ffc3d 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -55,10 +55,14 @@ struct vfsmount {
 
 struct file; /* forward dec */
 
+extern int __mnt_want_write(struct vfsmount *mnt);
 extern int mnt_want_write(struct vfsmount *mnt);
+extern int __mnt_want_write_file(struct file *file);
 extern int mnt_want_write_file(struct file *file);
 extern int mnt_clone_write(struct vfsmount *mnt);
+extern void __mnt_drop_write(struct vfsmount *mnt);
 extern void mnt_drop_write(struct vfsmount *mnt);
+extern void __mnt_drop_write_file(struct file *file);
 extern void mnt_drop_write_file(struct file *file);
 extern void mntput(struct vfsmount *mnt);
 extern struct vfsmount *mntget(struct vfsmount *mnt);
-- 
1.7.1

[PATCH 08/19] fs: Skip atime update on frozen filesystem

[Jan Kara]

It is unexpected to block reading of frozen filesystem because of atime update.
Also handling blocking on frozen filesystem because of atime update would make
locking more complex than it already is. So just skip atime update when
filesystem is frozen like we skip it when filesystem is remounted read-only.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/inode.c |    9 +++++++--
 1 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/fs/inode.c b/fs/inode.c
index 095828c..ff3b385 100644
--- a/fs/inode.c
+++ b/fs/inode.c
@@ -1535,12 +1535,17 @@ void touch_atime(struct vfsmount *mnt, struct dentry *dentry)
 	if (timespec_equal(&inode->i_atime, &now))
 		return;
 
-	if (mnt_want_write(mnt))
+	if (!sb_start_write_trylock(inode->i_sb))
 		return;
 
+	if (__mnt_want_write(mnt))
+		goto skip_update;
+
 	inode->i_atime = now;
 	mark_inode_dirty_sync(inode);
-	mnt_drop_write(mnt);
+	__mnt_drop_write(mnt);
+skip_update:
+	sb_end_write(inode->i_sb);
 }
 EXPORT_SYMBOL(touch_atime);
 
-- 
1.7.1

[PATCH 09/19] fs: Protect write paths by sb_start_write - sb_end_write

[Jan Kara]

There are several entry points which dirty pages in a filesystem.  mmap
(handled by block_page_mkwrite()), buffered write (handled by
__generic_file_aio_write()), splice write (generic_file_splice_write),
truncate, and fallocate (these can dirty last partial page - handled inside
each filesystem separately). Protect these places with sb_start_write() and
sb_end_write().

->page_mkwrite() calls are particularly complex since they are called with
mmap_sem held and thus we cannot use standard sb_start_write() due to lock
ordering constraints. We solve the problem by using a special freeze protection
sb_start_pagefault() which ranks below mmap_sem.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/buffer.c      |   22 ++++------------------
 fs/open.c        |    7 ++++++-
 fs/splice.c      |    3 +++
 mm/filemap.c     |   12 ++++++++++--
 mm/filemap_xip.c |    5 +++--
 5 files changed, 26 insertions(+), 23 deletions(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index 5294a33..89ed4af 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2288,8 +2288,8 @@ EXPORT_SYMBOL(block_commit_write);
  * beyond EOF, then the page is guaranteed safe against truncation until we
  * unlock the page.
  *
- * Direct callers of this function should call vfs_check_frozen() so that page
- * fault does not busyloop until the fs is thawed.
+ * Direct callers of this function should protect against filesystem freezing
+ * using sb_start_write() - sb_end_write() functions.
  */
 int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 			 get_block_t get_block)
@@ -2327,18 +2327,7 @@ int __block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 
 	if (unlikely(ret < 0))
 		goto out_unlock;
-	/*
-	 * Freezing in progress? We check after the page is marked dirty and
-	 * with page lock held so if the test here fails, we are sure freezing
-	 * code will wait during syncing until the page fault is done - at that
-	 * point page will be dirty and unlocked so freezing code will write it
-	 * and writeprotect it again.
-	 */
 	set_page_dirty(page);
-	if (inode->i_sb->s_frozen != SB_UNFROZEN) {
-		ret = -EAGAIN;
-		goto out_unlock;
-	}
 	wait_on_page_writeback(page);
 	return 0;
 out_unlock:
@@ -2353,12 +2342,9 @@ int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 	int ret;
 	struct super_block *sb = vma->vm_file->f_path.dentry->d_inode->i_sb;
 
-	/*
-	 * This check is racy but catches the common case. The check in
-	 * __block_page_mkwrite() is reliable.
-	 */
-	vfs_check_frozen(sb, SB_FREEZE_WRITE);
+	sb_start_pagefault(sb);
 	ret = __block_page_mkwrite(vma, vmf, get_block);
+	sb_end_pagefault(sb);
 	return block_page_mkwrite_return(ret);
 }
 EXPORT_SYMBOL(block_page_mkwrite);
diff --git a/fs/open.c b/fs/open.c
index 456e415..444ffbb 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -164,11 +164,13 @@ static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
 	if (IS_APPEND(inode))
 		goto out_putf;
 
+	sb_start_write(inode->i_sb);
 	error = locks_verify_truncate(inode, file, length);
 	if (!error)
 		error = security_path_truncate(&file->f_path);
 	if (!error)
 		error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, file);
+	sb_end_write(inode->i_sb);
 out_putf:
 	fput(file);
 out:
@@ -266,7 +268,10 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 	if (!file->f_op->fallocate)
 		return -EOPNOTSUPP;
 
-	return file->f_op->fallocate(file, mode, offset, len);
+	sb_start_write(inode->i_sb);
+	ret = file->f_op->fallocate(file, mode, offset, len);
+	sb_end_write(inode->i_sb);
+	return ret;
 }
 
 SYSCALL_DEFINE(fallocate)(int fd, int mode, loff_t offset, loff_t len)
diff --git a/fs/splice.c b/fs/splice.c
index 1ec0493..401297d 100644
--- a/fs/splice.c
+++ b/fs/splice.c
@@ -992,6 +992,8 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 	};
 	ssize_t ret;
 
+	sb_start_write(inode->i_sb);
+
 	pipe_lock(pipe);
 
 	splice_from_pipe_begin(&sd);
@@ -1028,6 +1030,7 @@ generic_file_splice_write(struct pipe_inode_info *pipe, struct file *out,
 			*ppos += ret;
 		balance_dirty_pages_ratelimited_nr(mapping, nr_pages);
 	}
+	sb_end_write(inode->i_sb);
 
 	return ret;
 }
diff --git a/mm/filemap.c b/mm/filemap.c
index fbd69e3..4cf9ad6 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1765,6 +1765,7 @@ int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
 	int ret = VM_FAULT_LOCKED;
 
+	sb_start_pagefault(inode->i_sb);
 	file_update_time(vma->vm_file);
 	lock_page(page);
 	if (page->mapping != inode->i_mapping) {
@@ -1772,7 +1773,14 @@ int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 		ret = VM_FAULT_NOPAGE;
 		goto out;
 	}
+	/*
+	 * We mark the page dirty already here so that when freeze is in
+	 * progress, we are guaranteed that writeback during freezing will
+	 * see the dirty page and writeprotect it again.
+	 */
+	set_page_dirty(page);
 out:
+	sb_end_pagefault(inode->i_sb);
 	return ret;
 }
 EXPORT_SYMBOL(filemap_page_mkwrite);
@@ -2536,8 +2544,6 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	count = ocount;
 	pos = *ppos;
 
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
-
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = mapping->backing_dev_info;
 	written = 0;
@@ -2634,6 +2640,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 
 	BUG_ON(iocb->ki_pos != pos);
 
+	sb_start_write(inode->i_sb);
 	mutex_lock(&inode->i_mutex);
 	blk_start_plug(&plug);
 	ret = __generic_file_aio_write(iocb, iov, nr_segs, &iocb->ki_pos);
@@ -2647,6 +2654,7 @@ ssize_t generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 			ret = err;
 	}
 	blk_finish_plug(&plug);
+	sb_end_write(inode->i_sb);
 	return ret;
 }
 EXPORT_SYMBOL(generic_file_aio_write);
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 591dba6..b051f0d 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -402,6 +402,8 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
 	loff_t pos;
 	ssize_t ret;
 
+	sb_start_write(inode->i_sb);
+
 	mutex_lock(&inode->i_mutex);
 
 	if (!access_ok(VERIFY_READ, buf, len)) {
@@ -412,8 +414,6 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
 	pos = *ppos;
 	count = len;
 
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
-
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = mapping->backing_dev_info;
 
@@ -435,6 +435,7 @@ xip_file_write(struct file *filp, const char __user *buf, size_t len,
 	current->backing_dev_info = NULL;
  out_up:
 	mutex_unlock(&inode->i_mutex);
+	sb_end_write(inode->i_sb);
 	return ret;
 }
 EXPORT_SYMBOL_GPL(xip_file_write);
-- 
1.7.1

[PATCH 10/19] ext4: Convert to new freezing mechanism

[Jan Kara]

We remove most of frozen checks since upper layer takes care
of blocking all writes. We only have to handle protection in
ext4_page_mkwrite() in a special way because we cannot use
generic block_page_mkwrite().

CC: linux-ext4@vger.kernel.org
CC: "Theodore Ts'o" <tytso@mit.edu>
BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/inode.c |    7 ++-----
 fs/ext4/mmp.c   |   14 ++++++++++----
 fs/ext4/super.c |   31 +++++++------------------------
 3 files changed, 19 insertions(+), 33 deletions(-)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index feaa82f..c65baf9 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -4593,11 +4593,7 @@ int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	get_block_t *get_block;
 	int retries = 0;
 
-	/*
-	 * This check is racy but catches the common case. We rely on
-	 * __block_page_mkwrite() to do a reliable check.
-	 */
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
+	sb_start_pagefault(inode->i_sb);
 	/* Delalloc case is easy... */
 	if (test_opt(inode->i_sb, DELALLOC) &&
 	    !ext4_should_journal_data(inode) &&
@@ -4665,5 +4661,6 @@ retry_alloc:
 out_ret:
 	ret = block_page_mkwrite_return(ret);
 out:
+	sb_end_pagefault(inode->i_sb);
 	return ret;
 }
diff --git a/fs/ext4/mmp.c b/fs/ext4/mmp.c
index 7ea4ba4..9061bc7 100644
--- a/fs/ext4/mmp.c
+++ b/fs/ext4/mmp.c
@@ -10,14 +10,20 @@
  * Write the MMP block using WRITE_SYNC to try to get the block on-disk
  * faster.
  */
-static int write_mmp_block(struct buffer_head *bh)
+static int write_mmp_block(struct super_block *sb, struct buffer_head *bh)
 {
+	/*
+	 * We protect against freezing so that we don't create dirty buffers
+	 * on frozen filesystem.
+	 */
+	sb_start_write(sb);
 	mark_buffer_dirty(bh);
 	lock_buffer(bh);
 	bh->b_end_io = end_buffer_write_sync;
 	get_bh(bh);
 	submit_bh(WRITE_SYNC, bh);
 	wait_on_buffer(bh);
+	sb_end_write(sb);
 	if (unlikely(!buffer_uptodate(bh)))
 		return 1;
 
@@ -120,7 +126,7 @@ static int kmmpd(void *data)
 		mmp->mmp_time = cpu_to_le64(get_seconds());
 		last_update_time = jiffies;
 
-		retval = write_mmp_block(bh);
+		retval = write_mmp_block(sb, bh);
 		/*
 		 * Don't spew too many error messages. Print one every
 		 * (s_mmp_update_interval * 60) seconds.
@@ -200,7 +206,7 @@ static int kmmpd(void *data)
 	mmp->mmp_seq = cpu_to_le32(EXT4_MMP_SEQ_CLEAN);
 	mmp->mmp_time = cpu_to_le64(get_seconds());
 
-	retval = write_mmp_block(bh);
+	retval = write_mmp_block(sb, bh);
 
 failed:
 	kfree(data);
@@ -299,7 +305,7 @@ skip:
 	seq = mmp_new_seq();
 	mmp->mmp_seq = cpu_to_le32(seq);
 
-	retval = write_mmp_block(bh);
+	retval = write_mmp_block(sb, bh);
 	if (retval)
 		goto failed;
 
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 502c61f..039b1e0 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -289,33 +289,17 @@ static void ext4_put_nojournal(handle_t *handle)
  * journal_end calls result in the superblock being marked dirty, so
  * that sync() will call the filesystem's write_super callback if
  * appropriate.
- *
- * To avoid j_barrier hold in userspace when a user calls freeze(),
- * ext4 prevents a new handle from being started by s_frozen, which
- * is in an upper layer.
  */
 handle_t *ext4_journal_start_sb(struct super_block *sb, int nblocks)
 {
 	journal_t *journal;
-	handle_t  *handle;
 
 	trace_ext4_journal_start(sb, nblocks, _RET_IP_);
 	if (sb->s_flags & MS_RDONLY)
 		return ERR_PTR(-EROFS);
 
+	WARN_ON(sb->s_writers.frozen == SB_FREEZE_COMPLETE);
 	journal = EXT4_SB(sb)->s_journal;
-	handle = ext4_journal_current_handle();
-
-	/*
-	 * If a handle has been started, it should be allowed to
-	 * finish, otherwise deadlock could happen between freeze
-	 * and others(e.g. truncate) due to the restart of the
-	 * journal handle if the filesystem is forzen and active
-	 * handles are not stopped.
-	 */
-	if (!handle)
-		vfs_check_frozen(sb, SB_FREEZE_TRANS);
-
 	if (!journal)
 		return ext4_get_nojournal();
 	/*
@@ -2772,6 +2756,7 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
 	sb = elr->lr_super;
 	ngroups = EXT4_SB(sb)->s_groups_count;
 
+	sb_start_write(sb);
 	for (group = elr->lr_next_group; group < ngroups; group++) {
 		gdp = ext4_get_group_desc(sb, group, NULL);
 		if (!gdp) {
@@ -2798,6 +2783,7 @@ static int ext4_run_li_request(struct ext4_li_request *elr)
 		elr->lr_next_sched = jiffies + elr->lr_timeout;
 		elr->lr_next_group = group + 1;
 	}
+	sb_end_write(sb);
 
 	return ret;
 }
@@ -4280,10 +4266,8 @@ int ext4_force_commit(struct super_block *sb)
 		return 0;
 
 	journal = EXT4_SB(sb)->s_journal;
-	if (journal) {
-		vfs_check_frozen(sb, SB_FREEZE_TRANS);
+	if (journal)
 		ret = ext4_journal_force_commit(journal);
-	}
 
 	return ret;
 }
@@ -4315,9 +4299,8 @@ static int ext4_sync_fs(struct super_block *sb, int wait)
  * gives us a chance to flush the journal completely and mark the fs clean.
  *
  * Note that only this function cannot bring a filesystem to be in a clean
- * state independently, because ext4 prevents a new handle from being started
- * by @sb->s_frozen, which stays in an upper layer.  It thus needs help from
- * the upper layer.
+ * state independently. It relies on upper layer to stop all data & metadata
+ * modifications.
  */
 static int ext4_freeze(struct super_block *sb)
 {
@@ -4344,7 +4327,7 @@ static int ext4_freeze(struct super_block *sb)
 	EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER);
 	error = ext4_commit_super(sb, 1);
 out:
-	/* we rely on s_frozen to stop further updates */
+	/* we rely on upper layer to stop further updates */
 	jbd2_journal_unlock_updates(EXT4_SB(sb)->s_journal);
 	return error;
 }
-- 
1.7.1

[PATCH 11/19] xfs: Convert to new freezing code

[Jan Kara]

Generic code now blocks all writers from standard write paths. So we add
blocking of all writers coming from ioctl (we get a protection of ioctl against
racing remount read-only as a bonus) and convert xfs_file_aio_write() to a
non-racy freeze protection. We also keep freeze protection on transaction
start to block internal filesystem writes such as removal of preallocated
blocks.

CC: Ben Myers <bpm@sgi.com>
CC: Alex Elder <elder@kernel.org>
CC: xfs@oss.sgi.com
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/xfs/xfs_file.c    |   10 ++++++--
 fs/xfs/xfs_ioctl.c   |   55 +++++++++++++++++++++++++++++++++++++++++++++++--
 fs/xfs/xfs_ioctl32.c |   12 ++++++++++
 fs/xfs/xfs_iomap.c   |    4 +-
 fs/xfs/xfs_mount.c   |    2 +-
 fs/xfs/xfs_mount.h   |    3 --
 fs/xfs/xfs_sync.c    |    2 +-
 fs/xfs/xfs_trans.c   |   17 ++++++++++++--
 fs/xfs/xfs_trans.h   |    2 +
 9 files changed, 91 insertions(+), 16 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 7e5bc87..57dd20e 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -874,10 +874,12 @@ xfs_file_aio_write(
 	if (ocount == 0)
 		return 0;
 
-	xfs_wait_for_freeze(ip->i_mount, SB_FREEZE_WRITE);
+	sb_start_write(inode->i_sb);
 
-	if (XFS_FORCED_SHUTDOWN(ip->i_mount))
-		return -EIO;
+	if (XFS_FORCED_SHUTDOWN(ip->i_mount)) {
+		ret = -EIO;
+		goto out;
+	}
 
 	if (unlikely(file->f_flags & O_DIRECT))
 		ret = xfs_file_dio_aio_write(iocb, iovp, nr_segs, pos, ocount);
@@ -896,6 +898,8 @@ xfs_file_aio_write(
 			ret = err;
 	}
 
+out:
+	sb_end_write(inode->i_sb);
 	return ret;
 }
 
diff --git a/fs/xfs/xfs_ioctl.c b/fs/xfs/xfs_ioctl.c
index 76f3ca5..7890105 100644
--- a/fs/xfs/xfs_ioctl.c
+++ b/fs/xfs/xfs_ioctl.c
@@ -367,9 +367,15 @@ xfs_fssetdm_by_handle(
 	if (copy_from_user(&dmhreq, arg, sizeof(xfs_fsop_setdm_handlereq_t)))
 		return -XFS_ERROR(EFAULT);
 
+	error = mnt_want_write_file(parfilp);
+	if (error)
+		return error;
+
 	dentry = xfs_handlereq_to_dentry(parfilp, &dmhreq.hreq);
-	if (IS_ERR(dentry))
+	if (IS_ERR(dentry)) {
+		mnt_drop_write_file(parfilp);
 		return PTR_ERR(dentry);
+	}
 
 	if (IS_IMMUTABLE(dentry->d_inode) || IS_APPEND(dentry->d_inode)) {
 		error = -XFS_ERROR(EPERM);
@@ -385,6 +391,7 @@ xfs_fssetdm_by_handle(
 				 fsd.fsd_dmstate);
 
  out:
+	mnt_drop_write_file(parfilp);
 	dput(dentry);
 	return error;
 }
@@ -631,7 +638,11 @@ xfs_ioc_space(
 	if (ioflags & IO_INVIS)
 		attr_flags |= XFS_ATTR_DMI;
 
+	error = mnt_want_write_file(filp);
+	if (error)
+		return error;
 	error = xfs_change_file_space(ip, cmd, bf, filp->f_pos, attr_flags);
+	mnt_drop_write_file(filp);
 	return -error;
 }
 
@@ -1160,6 +1171,7 @@ xfs_ioc_fssetxattr(
 {
 	struct fsxattr		fa;
 	unsigned int		mask;
+	int error;
 
 	if (copy_from_user(&fa, arg, sizeof(fa)))
 		return -EFAULT;
@@ -1168,7 +1180,12 @@ xfs_ioc_fssetxattr(
 	if (filp->f_flags & (O_NDELAY|O_NONBLOCK))
 		mask |= FSX_NONBLOCK;
 
-	return -xfs_ioctl_setattr(ip, &fa, mask);
+	error = mnt_want_write_file(filp);
+	if (error)
+		return error;
+	error = xfs_ioctl_setattr(ip, &fa, mask);
+	mnt_drop_write_file(filp);
+	return -error;
 }
 
 STATIC int
@@ -1193,6 +1210,7 @@ xfs_ioc_setxflags(
 	struct fsxattr		fa;
 	unsigned int		flags;
 	unsigned int		mask;
+	int error;
 
 	if (copy_from_user(&flags, arg, sizeof(flags)))
 		return -EFAULT;
@@ -1207,7 +1225,12 @@ xfs_ioc_setxflags(
 		mask |= FSX_NONBLOCK;
 	fa.fsx_xflags = xfs_merge_ioc_xflags(flags, xfs_ip2xflags(ip));
 
-	return -xfs_ioctl_setattr(ip, &fa, mask);
+	error = mnt_want_write_file(filp);
+	if (error)
+		return error;
+	error = xfs_ioctl_setattr(ip, &fa, mask);
+	mnt_drop_write_file(filp);
+	return -error;
 }
 
 STATIC int
@@ -1382,8 +1405,13 @@ xfs_file_ioctl(
 		if (copy_from_user(&dmi, arg, sizeof(dmi)))
 			return -XFS_ERROR(EFAULT);
 
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
+
 		error = xfs_set_dmattrs(ip, dmi.fsd_dmevmask,
 				dmi.fsd_dmstate);
+		mnt_drop_write_file(filp);
 		return -error;
 	}
 
@@ -1431,7 +1459,11 @@ xfs_file_ioctl(
 
 		if (copy_from_user(&sxp, arg, sizeof(xfs_swapext_t)))
 			return -XFS_ERROR(EFAULT);
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
 		error = xfs_swapext(&sxp);
+		mnt_drop_write_file(filp);
 		return -error;
 	}
 
@@ -1460,9 +1492,14 @@ xfs_file_ioctl(
 		if (copy_from_user(&inout, arg, sizeof(inout)))
 			return -XFS_ERROR(EFAULT);
 
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
+
 		/* input parameter is passed in resblks field of structure */
 		in = inout.resblks;
 		error = xfs_reserve_blocks(mp, &in, &inout);
+		mnt_drop_write_file(filp);
 		if (error)
 			return -error;
 
@@ -1493,7 +1530,11 @@ xfs_file_ioctl(
 		if (copy_from_user(&in, arg, sizeof(in)))
 			return -XFS_ERROR(EFAULT);
 
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
 		error = xfs_growfs_data(mp, &in);
+		mnt_drop_write_file(filp);
 		return -error;
 	}
 
@@ -1503,7 +1544,11 @@ xfs_file_ioctl(
 		if (copy_from_user(&in, arg, sizeof(in)))
 			return -XFS_ERROR(EFAULT);
 
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
 		error = xfs_growfs_log(mp, &in);
+		mnt_drop_write_file(filp);
 		return -error;
 	}
 
@@ -1513,7 +1558,11 @@ xfs_file_ioctl(
 		if (copy_from_user(&in, arg, sizeof(in)))
 			return -XFS_ERROR(EFAULT);
 
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
 		error = xfs_growfs_rt(mp, &in);
+		mnt_drop_write_file(filp);
 		return -error;
 	}
 
diff --git a/fs/xfs/xfs_ioctl32.c b/fs/xfs/xfs_ioctl32.c
index f9ccb7b..2012369 100644
--- a/fs/xfs/xfs_ioctl32.c
+++ b/fs/xfs/xfs_ioctl32.c
@@ -602,7 +602,11 @@ xfs_file_compat_ioctl(
 
 		if (xfs_compat_growfs_data_copyin(&in, arg))
 			return -XFS_ERROR(EFAULT);
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
 		error = xfs_growfs_data(mp, &in);
+		mnt_drop_write_file(filp);
 		return -error;
 	}
 	case XFS_IOC_FSGROWFSRT_32: {
@@ -610,7 +614,11 @@ xfs_file_compat_ioctl(
 
 		if (xfs_compat_growfs_rt_copyin(&in, arg))
 			return -XFS_ERROR(EFAULT);
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
 		error = xfs_growfs_rt(mp, &in);
+		mnt_drop_write_file(filp);
 		return -error;
 	}
 #endif
@@ -629,7 +637,11 @@ xfs_file_compat_ioctl(
 				   offsetof(struct xfs_swapext, sx_stat)) ||
 		    xfs_ioctl32_bstat_copyin(&sxp.sx_stat, &sxu->sx_stat))
 			return -XFS_ERROR(EFAULT);
+		error = mnt_want_write_file(filp);
+		if (error)
+			return error;
 		error = xfs_swapext(&sxp);
+		mnt_drop_write_file(filp);
 		return -error;
 	}
 	case XFS_IOC_FSBULKSTAT_32:
diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
index 246c7d5..2c35710 100644
--- a/fs/xfs/xfs_iomap.c
+++ b/fs/xfs/xfs_iomap.c
@@ -679,9 +679,9 @@ xfs_iomap_write_unwritten(
 		 * the same inode that we complete here and might deadlock
 		 * on the iolock.
 		 */
-		xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
+		sb_start_intwrite(mp->m_super);
 		tp = _xfs_trans_alloc(mp, XFS_TRANS_STRAT_WRITE, KM_NOFS);
-		tp->t_flags |= XFS_TRANS_RESERVE;
+		tp->t_flags |= XFS_TRANS_RESERVE | XFS_TRANS_FREEZE_PROT;
 		error = xfs_trans_reserve(tp, resblks,
 				XFS_WRITE_LOG_RES(mp), 0,
 				XFS_TRANS_PERM_LOG_RES,
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index d06afbc..bead529 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -1541,7 +1541,7 @@ xfs_unmountfs(
 int
 xfs_fs_writable(xfs_mount_t *mp)
 {
-	return !(xfs_test_for_freeze(mp) || XFS_FORCED_SHUTDOWN(mp) ||
+	return !(mp->m_super->s_writers.frozen || XFS_FORCED_SHUTDOWN(mp) ||
 		(mp->m_flags & XFS_MOUNT_RDONLY));
 }
 
diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index 19f69e2..f0afeb9 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -310,9 +310,6 @@ void xfs_do_force_shutdown(struct xfs_mount *mp, int flags, char *fname,
 #define SHUTDOWN_REMOTE_REQ	0x0010	/* shutdown came from remote cell */
 #define SHUTDOWN_DEVICE_REQ	0x0020	/* failed all paths to the device */
 
-#define xfs_test_for_freeze(mp)		((mp)->m_super->s_frozen)
-#define xfs_wait_for_freeze(mp,l)	vfs_check_frozen((mp)->m_super, (l))
-
 /*
  * Flags for xfs_mountfs
  */
diff --git a/fs/xfs/xfs_sync.c b/fs/xfs/xfs_sync.c
index 40b75ee..c44d687 100644
--- a/fs/xfs/xfs_sync.c
+++ b/fs/xfs/xfs_sync.c
@@ -498,7 +498,7 @@ xfs_sync_worker(
 
 	if (!(mp->m_flags & XFS_MOUNT_RDONLY)) {
 		/* dgc: errors ignored here */
-		if (mp->m_super->s_frozen == SB_UNFROZEN &&
+		if (mp->m_super->s_writers.frozen == SB_UNFROZEN &&
 		    xfs_log_need_covered(mp))
 			error = xfs_fs_log_dummy(mp);
 		else
diff --git a/fs/xfs/xfs_trans.c b/fs/xfs/xfs_trans.c
index 329b06a..12339b7 100644
--- a/fs/xfs/xfs_trans.c
+++ b/fs/xfs/xfs_trans.c
@@ -577,8 +577,12 @@ xfs_trans_alloc(
 	xfs_mount_t	*mp,
 	uint		type)
 {
-	xfs_wait_for_freeze(mp, SB_FREEZE_TRANS);
-	return _xfs_trans_alloc(mp, type, KM_SLEEP);
+	xfs_trans_t     *tp;
+
+	sb_start_intwrite(mp->m_super);
+	tp = _xfs_trans_alloc(mp, type, KM_SLEEP);
+	tp->t_flags |= XFS_TRANS_FREEZE_PROT;
+	return tp;
 }
 
 xfs_trans_t *
@@ -589,6 +593,7 @@ _xfs_trans_alloc(
 {
 	xfs_trans_t	*tp;
 
+	WARN_ON(mp->m_super->s_writers.frozen == SB_FREEZE_COMPLETE);
 	atomic_inc(&mp->m_active_trans);
 
 	tp = kmem_zone_zalloc(xfs_trans_zone, memflags);
@@ -612,6 +617,8 @@ xfs_trans_free(
 	xfs_alloc_busy_clear(tp->t_mountp, &tp->t_busy, false);
 
 	atomic_dec(&tp->t_mountp->m_active_trans);
+	if (tp->t_flags & XFS_TRANS_FREEZE_PROT)
+		sb_end_intwrite(tp->t_mountp->m_super);
 	xfs_trans_free_dqinfo(tp);
 	kmem_zone_free(xfs_trans_zone, tp);
 }
@@ -644,7 +651,11 @@ xfs_trans_dup(
 	ASSERT(tp->t_flags & XFS_TRANS_PERM_LOG_RES);
 	ASSERT(tp->t_ticket != NULL);
 
-	ntp->t_flags = XFS_TRANS_PERM_LOG_RES | (tp->t_flags & XFS_TRANS_RESERVE);
+	ntp->t_flags = XFS_TRANS_PERM_LOG_RES |
+		       (tp->t_flags & XFS_TRANS_RESERVE) |
+		       (tp->t_flags & XFS_TRANS_FREEZE_PROT);
+	/* We gave our writer reference to the new transaction */
+	tp->t_flags &= ~XFS_TRANS_FREEZE_PROT;
 	ntp->t_ticket = xfs_log_ticket_get(tp->t_ticket);
 	ntp->t_blk_res = tp->t_blk_res - tp->t_blk_res_used;
 	tp->t_blk_res = tp->t_blk_res_used;
diff --git a/fs/xfs/xfs_trans.h b/fs/xfs/xfs_trans.h
index f611870..e42d94e 100644
--- a/fs/xfs/xfs_trans.h
+++ b/fs/xfs/xfs_trans.h
@@ -179,6 +179,8 @@ struct xfs_log_item_desc {
 #define	XFS_TRANS_SYNC		0x08	/* make commit synchronous */
 #define XFS_TRANS_DQ_DIRTY	0x10	/* at least one dquot in trx dirty */
 #define XFS_TRANS_RESERVE	0x20    /* OK to use reserved data blocks */
+#define XFS_TRANS_FREEZE_PROT	0x40	/* Transaction has elevated writer
+					   count in superblock */
 
 /*
  * Values for call flags parameter.
-- 
1.7.1

[PATCH 12/19] ocfs2: Convert to new freezing mechanism

[Jan Kara]

Protect ocfs2_page_mkwrite() and ocfs2_file_aio_write() using the new
freeze protection. We also protect several ioctl entry points which
were missing the protection.

CC: Mark Fasheh <mfasheh@suse.com>
CC: Joel Becker <jlbec@evilplan.org>
CC: ocfs2-devel@oss.oracle.com
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ocfs2/file.c  |   11 +++++++++--
 fs/ocfs2/ioctl.c |   14 ++++++++++++--
 fs/ocfs2/mmap.c  |    2 ++
 3 files changed, 23 insertions(+), 4 deletions(-)

diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
index 061591a..9b1e3d4 100644
--- a/fs/ocfs2/file.c
+++ b/fs/ocfs2/file.c
@@ -1971,6 +1971,7 @@ int ocfs2_change_file_space(struct file *file, unsigned int cmd,
 {
 	struct inode *inode = file->f_path.dentry->d_inode;
 	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
+	int ret;
 
 	if ((cmd == OCFS2_IOC_RESVSP || cmd == OCFS2_IOC_RESVSP64) &&
 	    !ocfs2_writes_unwritten_extents(osb))
@@ -1985,7 +1986,12 @@ int ocfs2_change_file_space(struct file *file, unsigned int cmd,
 	if (!(file->f_mode & FMODE_WRITE))
 		return -EBADF;
 
-	return __ocfs2_change_file_space(file, inode, file->f_pos, cmd, sr, 0);
+	ret = mnt_want_write_file(file);
+	if (ret)
+		return ret;
+	ret = __ocfs2_change_file_space(file, inode, file->f_pos, cmd, sr, 0);
+	mnt_drop_write_file(file);
+	return ret;
 }
 
 static long ocfs2_fallocate(struct file *file, int mode, loff_t offset,
@@ -2261,7 +2267,7 @@ static ssize_t ocfs2_file_aio_write(struct kiocb *iocb,
 	if (iocb->ki_left == 0)
 		return 0;
 
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
+	sb_start_write(inode->i_sb);
 
 	appending = file->f_flags & O_APPEND ? 1 : 0;
 	direct_io = file->f_flags & O_DIRECT ? 1 : 0;
@@ -2434,6 +2440,7 @@ out_sems:
 		ocfs2_iocb_clear_sem_locked(iocb);
 
 	mutex_unlock(&inode->i_mutex);
+	sb_end_write(inode->i_sb);
 
 	if (written)
 		ret = written;
diff --git a/fs/ocfs2/ioctl.c b/fs/ocfs2/ioctl.c
index a6fda3c..59de312 100644
--- a/fs/ocfs2/ioctl.c
+++ b/fs/ocfs2/ioctl.c
@@ -928,7 +928,12 @@ long ocfs2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		if (get_user(new_clusters, (int __user *)arg))
 			return -EFAULT;
 
-		return ocfs2_group_extend(inode, new_clusters);
+		status = mnt_want_write_file(filp);
+		if (status)
+			return status;
+		status = ocfs2_group_extend(inode, new_clusters);
+		mnt_drop_write_file(filp);
+		return status;
 	case OCFS2_IOC_GROUP_ADD:
 	case OCFS2_IOC_GROUP_ADD64:
 		if (!capable(CAP_SYS_RESOURCE))
@@ -937,7 +942,12 @@ long ocfs2_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		if (copy_from_user(&input, (int __user *) arg, sizeof(input)))
 			return -EFAULT;
 
-		return ocfs2_group_add(inode, &input);
+		status = mnt_want_write_file(filp);
+		if (status)
+			return status;
+		status = ocfs2_group_add(inode, &input);
+		mnt_drop_write_file(filp);
+		return status;
 	case OCFS2_IOC_REFLINK:
 		if (copy_from_user(&args, (struct reflink_arguments *)arg,
 				   sizeof(args)))
diff --git a/fs/ocfs2/mmap.c b/fs/ocfs2/mmap.c
index 9cd4108..d150372 100644
--- a/fs/ocfs2/mmap.c
+++ b/fs/ocfs2/mmap.c
@@ -136,6 +136,7 @@ static int ocfs2_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	sigset_t oldset;
 	int ret;
 
+	sb_start_pagefault(inode->i_sb);
 	ocfs2_block_signals(&oldset);
 
 	/*
@@ -165,6 +166,7 @@ static int ocfs2_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 
 out:
 	ocfs2_unblock_signals(&oldset);
+	sb_end_pagefault(inode->i_sb);
 	return ret;
 }
 
-- 
1.7.1

[PATCH 13/19] gfs2: Convert to new freezing mechanism

[Jan Kara]

It is enough to update gfs2_page_mkwrite() to use new freeze protection.
Rest is handled by the generic code.

CC: cluster-devel@redhat.com
CC: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/gfs2/file.c |   15 +++------------
 1 files changed, 3 insertions(+), 12 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index 1f03531..806b7a4 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -369,11 +369,7 @@ static int gfs2_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	loff_t size;
 	int ret;
 
-	/* Wait if fs is frozen. This is racy so we check again later on
-	 * and retry if the fs has been frozen after the page lock has
-	 * been acquired
-	 */
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
+	sb_start_pagefault(inode->i_sb);
 
 	/* Update file times before taking page lock */
 	file_update_time(vma->vm_file);
@@ -457,14 +453,9 @@ out:
 	gfs2_holder_uninit(&gh);
 	if (ret == 0) {
 		set_page_dirty(page);
-		/* This check must be post dropping of transaction lock */
-		if (inode->i_sb->s_frozen == SB_UNFROZEN) {
-			wait_on_page_writeback(page);
-		} else {
-			ret = -EAGAIN;
-			unlock_page(page);
-		}
+		wait_on_page_writeback(page);
 	}
+	sb_end_pagefault(inode->i_sb);
 	return block_page_mkwrite_return(ret);
 }
 
-- 
1.7.1

[PATCH 14/19] fuse: Convert to new freezing mechanism

[Jan Kara]

Convert check in fuse_file_aio_write() to using new freeze protection.

CC: fuse-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
CC: Miklos Szeredi <miklos-sUDqSbJrdHQHWmgEVkV9KA@public.gmane.org>
Signed-off-by: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
---
 fs/fuse/file.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index eade72e..05f661f 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -943,8 +943,8 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	if (err)
 		return err;
 
+	sb_start_write(inode->i_sb);
 	mutex_lock(&inode->i_mutex);
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
 
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = mapping->backing_dev_info;
@@ -970,6 +970,7 @@ static ssize_t fuse_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 out:
 	current->backing_dev_info = NULL;
 	mutex_unlock(&inode->i_mutex);
+	sb_end_write(inode->i_sb);
 
 	return written ? written : err;
 }
-- 
1.7.1


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[PATCH 15/19] ntfs: Convert to new freezing mechanism

[Jan Kara]

Move check in ntfs_file_aio_write_nolock() to ntfs_file_aio_write() and
use new freeze protection.

CC: linux-ntfs-dev@lists.sourceforge.net
CC: Anton Altaparmakov <anton@tuxera.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ntfs/file.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/fs/ntfs/file.c b/fs/ntfs/file.c
index c587e2d..0503e65 100644
--- a/fs/ntfs/file.c
+++ b/fs/ntfs/file.c
@@ -2084,7 +2084,6 @@ static ssize_t ntfs_file_aio_write_nolock(struct kiocb *iocb,
 	if (err)
 		return err;
 	pos = *ppos;
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
 	/* We can write back this queue in page reclaim. */
 	current->backing_dev_info = mapping->backing_dev_info;
 	written = 0;
@@ -2117,6 +2116,7 @@ static ssize_t ntfs_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 
 	BUG_ON(iocb->ki_pos != pos);
 
+	sb_start_write(inode->i_sb);
 	mutex_lock(&inode->i_mutex);
 	ret = ntfs_file_aio_write_nolock(iocb, iov, nr_segs, &iocb->ki_pos);
 	mutex_unlock(&inode->i_mutex);
@@ -2125,6 +2125,7 @@ static ssize_t ntfs_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 		if (err < 0)
 			ret = err;
 	}
+	sb_end_write(inode->i_sb);
 	return ret;
 }
 
-- 
1.7.1

[PATCH 16/19] nilfs2: Convert to new freezing mechanism

[Jan Kara]

We change nilfs_page_mkwrite() to provide proper freeze protection for
writeable page faults (we must wait for frozen filesystem even if the
page is fully mapped).

We remove all vfs_check_frozen() checks since they are now handled by
the generic code.

CC: linux-nilfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
CC: KONISHI Ryusuke <konishi.ryusuke-Zyj7fXuS5i5L9jVzuh4AOg@public.gmane.org>
Signed-off-by: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
---
 fs/nilfs2/file.c    |   18 +++++++++++-------
 fs/nilfs2/ioctl.c   |    2 --
 fs/nilfs2/segment.c |    5 ++++-
 3 files changed, 15 insertions(+), 10 deletions(-)

diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
index 2660152..0cdd702 100644
--- a/fs/nilfs2/file.c
+++ b/fs/nilfs2/file.c
@@ -65,16 +65,18 @@ static int nilfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	struct page *page = vmf->page;
 	struct inode *inode = vma->vm_file->f_dentry->d_inode;
 	struct nilfs_transaction_info ti;
-	int ret;
+	int ret = 0;
 
 	if (unlikely(nilfs_near_disk_full(inode->i_sb->s_fs_info)))
 		return VM_FAULT_SIGBUS; /* -ENOSPC */
 
+	sb_start_pagefault(inode->i_sb);
 	lock_page(page);
 	if (page->mapping != inode->i_mapping ||
 	    page_offset(page) >= i_size_read(inode) || !PageUptodate(page)) {
 		unlock_page(page);
-		return VM_FAULT_NOPAGE; /* make the VM retry the fault */
+		ret = -EFAULT;	/* make the VM retry the fault */
+		goto out;
 	}
 
 	/*
@@ -108,19 +110,21 @@ static int nilfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	ret = nilfs_transaction_begin(inode->i_sb, &ti, 1);
 	/* never returns -ENOMEM, but may return -ENOSPC */
 	if (unlikely(ret))
-		return VM_FAULT_SIGBUS;
+		goto out;
 
-	ret = block_page_mkwrite(vma, vmf, nilfs_get_block);
-	if (ret != VM_FAULT_LOCKED) {
+	ret = __block_page_mkwrite(vma, vmf, nilfs_get_block);
+	if (ret) {
 		nilfs_transaction_abort(inode->i_sb);
-		return ret;
+		goto out;
 	}
 	nilfs_set_file_dirty(inode, 1 << (PAGE_SHIFT - inode->i_blkbits));
 	nilfs_transaction_commit(inode->i_sb);
 
  mapped:
 	wait_on_page_writeback(page);
-	return VM_FAULT_LOCKED;
+ out:
+	sb_end_pagefault(inode->i_sb);
+	return block_page_mkwrite_return(ret);
 }
 
 static const struct vm_operations_struct nilfs_file_vm_ops = {
diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index 2a70fce..a2063c7 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -660,8 +660,6 @@ static int nilfs_ioctl_clean_segments(struct inode *inode, struct file *filp,
 		goto out_free;
 	}
 
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
-
 	ret = nilfs_ioctl_move_blocks(inode->i_sb, &argv[0], kbufs[0]);
 	if (ret < 0)
 		printk(KERN_ERR "NILFS: GC failed during preparation: "
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 0e72ad6..627351a 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -189,7 +189,7 @@ int nilfs_transaction_begin(struct super_block *sb,
 	if (ret > 0)
 		return 0;
 
-	vfs_check_frozen(sb, SB_FREEZE_WRITE);
+	sb_start_intwrite(sb);
 
 	nilfs = sb->s_fs_info;
 	down_read(&nilfs->ns_segctor_sem);
@@ -205,6 +205,7 @@ int nilfs_transaction_begin(struct super_block *sb,
 	current->journal_info = ti->ti_save;
 	if (ti->ti_flags & NILFS_TI_DYNAMIC_ALLOC)
 		kmem_cache_free(nilfs_transaction_cachep, ti);
+	sb_end_intwrite(sb);
 	return ret;
 }
 
@@ -246,6 +247,7 @@ int nilfs_transaction_commit(struct super_block *sb)
 		err = nilfs_construct_segment(sb);
 	if (ti->ti_flags & NILFS_TI_DYNAMIC_ALLOC)
 		kmem_cache_free(nilfs_transaction_cachep, ti);
+	sb_end_intwrite(sb);
 	return err;
 }
 
@@ -264,6 +266,7 @@ void nilfs_transaction_abort(struct super_block *sb)
 	current->journal_info = ti->ti_save;
 	if (ti->ti_flags & NILFS_TI_DYNAMIC_ALLOC)
 		kmem_cache_free(nilfs_transaction_cachep, ti);
+	sb_end_intwrite(sb);
 }
 
 void nilfs_relax_pressure_in_lock(struct super_block *sb)
-- 
1.7.1

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[PATCH 17/19] btrfs: Convert to new freezing mechanism

[Jan Kara]

We convert btrfs_file_aio_write() to use new freeze check.  We also add proper
freeze protection to btrfs_page_mkwrite(). Checks in cleaner_kthread() and
transaction_kthread() can be safely removed since btrfs_freeze() will lock
the mutexes and thus block the threads (and they shouldn't have anything to
do anyway).

CC: linux-btrfs@vger.kernel.org
CC: Chris Mason <chris.mason@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/btrfs/disk-io.c |    3 ---
 fs/btrfs/file.c    |    3 ++-
 fs/btrfs/inode.c   |    6 +++++-
 3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 811d9f9..fc0f74c 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1586,8 +1586,6 @@ static int cleaner_kthread(void *arg)
 	struct btrfs_root *root = arg;
 
 	do {
-		vfs_check_frozen(root->fs_info->sb, SB_FREEZE_WRITE);
-
 		if (!(root->fs_info->sb->s_flags & MS_RDONLY) &&
 		    mutex_trylock(&root->fs_info->cleaner_mutex)) {
 			btrfs_run_delayed_iputs(root);
@@ -1618,7 +1616,6 @@ static int transaction_kthread(void *arg)
 
 	do {
 		delay = HZ * 30;
-		vfs_check_frozen(root->fs_info->sb, SB_FREEZE_WRITE);
 		mutex_lock(&root->fs_info->transaction_kthread_mutex);
 
 		spin_lock(&root->fs_info->trans_lock);
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 859ba2d..1aac7ca 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -1348,7 +1348,7 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 	ssize_t err = 0;
 	size_t count, ocount;
 
-	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
+	sb_start_write(inode->i_sb);
 
 	mutex_lock(&inode->i_mutex);
 
@@ -1439,6 +1439,7 @@ static ssize_t btrfs_file_aio_write(struct kiocb *iocb,
 			num_written = err;
 	}
 out:
+	sb_end_write(inode->i_sb);
 	current->backing_dev_info = NULL;
 	return num_written ? num_written : err;
 }
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 32214fe..63c9006 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -6405,6 +6405,7 @@ int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	u64 page_start;
 	u64 page_end;
 
+	sb_start_pagefault(inode->i_sb);
 	ret  = btrfs_delalloc_reserve_space(inode, PAGE_CACHE_SIZE);
 	if (!ret) {
 		ret = btrfs_update_time(vma->vm_file);
@@ -6495,12 +6496,15 @@ again:
 	unlock_extent_cached(io_tree, page_start, page_end, &cached_state, GFP_NOFS);
 
 out_unlock:
-	if (!ret)
+	if (!ret) {
+		sb_end_pagefault(inode->i_sb);
 		return VM_FAULT_LOCKED;
+	}
 	unlock_page(page);
 out:
 	btrfs_delalloc_release_space(inode, PAGE_CACHE_SIZE);
 out_noreserve:
+	sb_end_pagefault(inode->i_sb);
 	return ret;
 }
 
-- 
1.7.1

[PATCH 18/19] fs: Remove old freezing mechanism

[Jan Kara]

Now that all users are converted, we can remove functions, variables, and
constants defined by the old freezing mechanism.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/super.c         |    1 -
 include/linux/fs.h |    9 ---------
 2 files changed, 0 insertions(+), 10 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index 9203907..ff21b59 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -216,7 +216,6 @@ static struct super_block *alloc_super(struct file_system_type *type)
 		mutex_init(&s->s_dquot.dqio_mutex);
 		mutex_init(&s->s_dquot.dqonoff_mutex);
 		init_rwsem(&s->s_dquot.dqptr_sem);
-		init_waitqueue_head(&s->s_wait_unfrozen);
 		s->s_maxbytes = MAX_NON_LFS;
 		s->s_op = &default_op;
 		s->s_time_gran = 1000000000;
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 2c7c7bf..89678b5 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1420,7 +1420,6 @@ extern spinlock_t sb_lock;
 enum {
 	SB_UNFROZEN = 0,		/* FS is unfrozen */
 	SB_FREEZE_WRITE	= 1,		/* Writes, dir ops, ioctls frozen */
-	SB_FREEZE_TRANS = 2,
 	SB_FREEZE_PAGEFAULT = 2,	/* Page faults stopped as well */
 	SB_FREEZE_FS = 3,		/* For internal FS use (e.g. to stop
 					 * internal threads if needed) */
@@ -1489,8 +1488,6 @@ struct super_block {
 	struct hlist_node	s_instances;
 	struct quota_info	s_dquot;	/* Diskquota specific options */
 
-	int			s_frozen;
-	wait_queue_head_t	s_wait_unfrozen;
 	struct sb_writers	s_writers;
 
 	char s_id[32];				/* Informational name */
@@ -1543,12 +1540,6 @@ extern void prune_dcache_sb(struct super_block *sb, int nr_to_scan);
 extern struct timespec current_fs_time(struct super_block *sb);
 
 /*
- * Snapshotting support.
- */
-/* Will go away when all users are converted */
-#define vfs_check_frozen(sb, level) do { } while (0)
-
-/*
  * until VFS tracks user namespaces for inodes, just make all files
  * belong to init_user_ns
  */
-- 
1.7.1

[PATCH 19/19] fs: Refuse to freeze filesystem with open but unlinked files

[Jan Kara]

Filesystem with frozen but unlinked files cannot be forced into
a fully consistent state. Also handling of closing such files on frozen
filesystem is problematic since fput() can be called with mmap_sem held
and protection against frozen filesystem ranks above it.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/super.c |   26 +++++++++++++++++++-------
 1 files changed, 19 insertions(+), 7 deletions(-)

diff --git a/fs/super.c b/fs/super.c
index ff21b59..8686417 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1459,16 +1459,22 @@ int freeze_super(struct super_block *sb)
 	smp_wmb();
 	sb_wait_write(sb, SB_FREEZE_FS);
 
+	/*
+	 * Check whether there are some open unlinked files (since all writers
+	 * are blocked, new ones cannot be created now so the check is
+	 * reliable). In that case filesystem cannot be forced into a
+	 * consistent state so we just bail out.
+	 */
+	if (atomic_long_read(&sb->s_remove_count)) {
+		ret = -EBUSY;
+		goto bail;
+	}
+
 	if (sb->s_op->freeze_fs) {
 		ret = sb->s_op->freeze_fs(sb);
 		if (ret) {
-			printk(KERN_ERR
-				"VFS:Filesystem freeze failed\n");
-			sb->s_writers.frozen = SB_UNFROZEN;
-			smp_wmb();
-			wake_up(&sb->s_writers.wait_unfrozen);
-			deactivate_locked_super(sb);
-			return ret;
+			printk(KERN_ERR "VFS: Filesystem freeze failed\n");
+			goto bail;
 		}
 	}
 	/*
@@ -1478,6 +1484,12 @@ int freeze_super(struct super_block *sb)
 	sb->s_writers.frozen = SB_FREEZE_COMPLETE;
 	up_write(&sb->s_umount);
 	return 0;
+bail:
+	sb->s_writers.frozen = SB_UNFROZEN;
+	smp_wmb();
+	wake_up(&sb->s_writers.wait_unfrozen);
+	deactivate_locked_super(sb);
+	return ret;
 }
 EXPORT_SYMBOL(freeze_super);
 
-- 
1.7.1

Re: [PATCH 07/19] fs: Add freezing handling to mnt_want_write() / mnt_drop_write()

[Szeredi Miklos]

On Thu, Mar 29, 2012 at 1:43 AM, Jan Kara <jack@suse.cz> wrote:
> Most of places where we want freeze protection coincides with the places where
> we also have remount-ro protection. So make mnt_want_write() and
> mnt_drop_write() (and their _file alternative) prevent freezing as well.
> For the few cases that are really interested only in remount-ro protection
> provide new function variants.

The underlying mechanism of mnt_want_write() and sb_start_write() is
basically the same:

 - increment per-CPU counter
 - mb
 - check flag
 - retry loop for races

It is scalable but still there is a non-zero overhead, and duplicating
it doesn't seem to make a lot of sense.  Why not instead try to use a
common abstraction for both?

Then the success case will be common, only the relatively rare failure
case needs to be handled separately.

Thanks,
Miklos

Re: [PATCH 13/19] gfs2: Convert to new freezing mechanism

[Steven Whitehouse]

Hi,

On Thu, 2012-03-29 at 01:43 +0200, Jan Kara wrote:
> It is enough to update gfs2_page_mkwrite() to use new freeze protection.
> Rest is handled by the generic code.
> 
> CC: cluster-devel@redhat.com
> CC: Steven Whitehouse <swhiteho@redhat.com>
> Signed-off-by: Jan Kara <jack@suse.cz>

I think that looks ok to me...

Acked-by: Steven Whitehouse <swhiteho@redhat.com>

Steve.

> ---
>  fs/gfs2/file.c |   15 +++------------
>  1 files changed, 3 insertions(+), 12 deletions(-)
> 
> diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
> index 1f03531..806b7a4 100644
> --- a/fs/gfs2/file.c
> +++ b/fs/gfs2/file.c
> @@ -369,11 +369,7 @@ static int gfs2_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  	loff_t size;
>  	int ret;
>  
> -	/* Wait if fs is frozen. This is racy so we check again later on
> -	 * and retry if the fs has been frozen after the page lock has
> -	 * been acquired
> -	 */
> -	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
> +	sb_start_pagefault(inode->i_sb);
>  
>  	/* Update file times before taking page lock */
>  	file_update_time(vma->vm_file);
> @@ -457,14 +453,9 @@ out:
>  	gfs2_holder_uninit(&gh);
>  	if (ret == 0) {
>  		set_page_dirty(page);
> -		/* This check must be post dropping of transaction lock */
> -		if (inode->i_sb->s_frozen == SB_UNFROZEN) {
> -			wait_on_page_writeback(page);
> -		} else {
> -			ret = -EAGAIN;
> -			unlock_page(page);
> -		}
> +		wait_on_page_writeback(page);
>  	}
> +	sb_end_pagefault(inode->i_sb);
>  	return block_page_mkwrite_return(ret);
>  }
>  

Re: [PATCH 07/19] fs: Add freezing handling to mnt_want_write() / mnt_drop_write()

[Jan Kara]

On Thu 29-03-12 12:19:43, Szeredi Miklos wrote:
> On Thu, Mar 29, 2012 at 1:43 AM, Jan Kara <jack@suse.cz> wrote:
> > Most of places where we want freeze protection coincides with the places where
> > we also have remount-ro protection. So make mnt_want_write() and
> > mnt_drop_write() (and their _file alternative) prevent freezing as well.
> > For the few cases that are really interested only in remount-ro protection
> > provide new function variants.
> 
> The underlying mechanism of mnt_want_write() and sb_start_write() is
> basically the same:
> 
>  - increment per-CPU counter
>  - mb
>  - check flag
>  - retry loop for races
  Well, __mnt_want_write() has the special handling of MNT_WRITE_HOLD.
Otherwise yes, the locking logic is rather similar.

> It is scalable but still there is a non-zero overhead, and duplicating
> it doesn't seem to make a lot of sense.  Why not instead try to use a
> common abstraction for both?
  I'm not sure here. Are you concerned about performance - i.e. you would
like to merge the remount-ro counter and topmost anti-freeze counter? That
cannot work because in some cases you want remount-ro protection but not
freezing protection. In particular when you have file open for writing,
you want to refuse remount-ro but still allow freezing.

If you are concerned about code / source size, the implementations of the
protection mechanisms could be possibly merged but I'm not sure it's worth
the hassle since we'd save like 50 LOC. MNT_WRITE_HOLD is one difference,
how each of the implementation detects whether we have succeeded in taking
our lock is another difference...

								Honza
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR

Re: [PATCH 07/19] fs: Add freezing handling to mnt_want_write() / mnt_drop_write()

[Miklos Szeredi]

On Thu, Mar 29, 2012 at 2:11 PM, Jan Kara <jack@suse.cz> wrote:
> On Thu 29-03-12 12:19:43, Szeredi Miklos wrote:
>> On Thu, Mar 29, 2012 at 1:43 AM, Jan Kara <jack@suse.cz> wrote:
>> > Most of places where we want freeze protection coincides with the places where
>> > we also have remount-ro protection. So make mnt_want_write() and
>> > mnt_drop_write() (and their _file alternative) prevent freezing as well.
>> > For the few cases that are really interested only in remount-ro protection
>> > provide new function variants.
>>
>> The underlying mechanism of mnt_want_write() and sb_start_write() is
>> basically the same:
>>
>>  - increment per-CPU counter
>>  - mb
>>  - check flag
>>  - retry loop for races
>  Well, __mnt_want_write() has the special handling of MNT_WRITE_HOLD.
> Otherwise yes, the locking logic is rather similar.
>
>> It is scalable but still there is a non-zero overhead, and duplicating
>> it doesn't seem to make a lot of sense.  Why not instead try to use a
>> common abstraction for both?
>  I'm not sure here. Are you concerned about performance  - i.e. you would
> like to merge the remount-ro counter and topmost anti-freeze counter?

Yes.

>  That
> cannot work because in some cases you want remount-ro protection but not
> freezing protection. In particular when you have file open for writing,
> you want to refuse remount-ro but still allow freezing.

Well, you could have a separate counter that keeps track of the
difference, which just needs to be modified when the two counters
diverge (i.e. when opening a file for write and when releasing that
file).  But yeah, it may not be worth it.

Thanks,
Miklos
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