[Cluster-devel] [PATCH 00/27 v7] Fix filesystem freezing deadlocks

[Cluster-devel] [PATCH 00/27 v7] Fix filesystem freezing deadlocks

[Jan Kara]

  Hello,

  here is the seventh iteration of my patches to improve filesystem freezing.
I've rebased patches on top of 3.5-rc2 as Al requested. Otherwise I've just
fixed some outdated text in the introduction below and added one ack.

Introductory text to first time readers:

Filesystem freezing is currently racy and thus we can end up with dirty data on
frozen filesystem (see changelog patch 13 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
file_update_time() call to ->page_mkwrite callback (patches 01-07) and put
freeze handling in mnt_want_write() / mnt_drop_write(). That however required
some code shuffling and changes to kern_path_create() (see patches 09-12). 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.

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

Changes since v6:
  * rebased on 3.5-rc2
  * added ack

Changes since v5:
  * handle unlinked & open files on frozen filesystem
  * lockdep keys for freeze protection are now per filesystem type
  * taught lockdep that freeze protection at lower level does not create
    dependency when we already hold freeze protection at higher level 
  * rebased on 3.5-rc1-ish

Changes since v4:
  * added a couple of Acked-by's
  * added some comments & doc update
  * added patches from series "Push file_update_time() into .page_mkwrite"
    since it doesn't make much sense to keep them separate anymore
  * rebased on top of 3.4-rc2

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@kernel.org>
CC: Anton Altaparmakov <anton@tuxera.com>
CC: Ben Myers <bpm@sgi.com>
CC: Chris Mason <chris.mason@oracle.com>
CC: cluster-devel at redhat.com
CC: "David S. Miller" <davem@davemloft.net>
CC: fuse-devel at lists.sourceforge.net
CC: "J. Bruce Fields" <bfields@fieldses.org>
CC: Joel Becker <jlbec@evilplan.org>
CC: KONISHI Ryusuke <konishi.ryusuke@lab.ntt.co.jp>
CC: linux-btrfs at vger.kernel.org
CC: linux-ext4 at vger.kernel.org
CC: linux-nfs at vger.kernel.org
CC: linux-nilfs at vger.kernel.org
CC: linux-ntfs-dev at lists.sourceforge.net
CC: Mark Fasheh <mfasheh@suse.com>
CC: Miklos Szeredi <miklos@szeredi.hu>
CC: ocfs2-devel at oss.oracle.com
CC: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
CC: Steven Whitehouse <swhiteho@redhat.com>
CC: "Theodore Ts'o" <tytso@mit.edu>
CC: xfs at oss.sgi.com

[Cluster-devel] [PATCH 05/27] gfs2: Push file_update_time() into gfs2_page_mkwrite()

[Jan Kara]

CC: Steven Whitehouse <swhiteho@redhat.com>
CC: cluster-devel at redhat.com
Acked-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/gfs2/file.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index 31b199f..0795915 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -376,6 +376,9 @@ static int gfs2_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 	 */
 	vfs_check_frozen(inode->i_sb, SB_FREEZE_WRITE);
 
+	/* Update file times before taking page lock */
+	file_update_time(vma->vm_file);
+
 	gfs2_holder_init(ip->i_gl, LM_ST_EXCLUSIVE, 0, &gh);
 	ret = gfs2_glock_nq(&gh);
 	if (ret)
-- 
1.7.1

[Cluster-devel] [PATCH 20/27] gfs2: Convert to new freezing mechanism

[Jan Kara]

We update gfs2_page_mkwrite() to use new freeze protection and the transaction
code to use freeze protection while the transaction is running. That is needed
to stop iput() of unlinked file from modifying the filesystem. The rest is
handled by the generic code.

CC: cluster-devel at redhat.com
CC: Steven Whitehouse <swhiteho@redhat.com>
Acked-by: Steven Whitehouse <swhiteho@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/gfs2/file.c  |   15 +++------------
 fs/gfs2/trans.c |    4 ++++
 2 files changed, 7 insertions(+), 12 deletions(-)

diff --git a/fs/gfs2/file.c b/fs/gfs2/file.c
index 0795915..8ffeb03 100644
--- a/fs/gfs2/file.c
+++ b/fs/gfs2/file.c
@@ -370,11 +370,7 @@ 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);
@@ -458,14 +454,9 @@ 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);
 }
 
diff --git a/fs/gfs2/trans.c b/fs/gfs2/trans.c
index ad3e2fb..adbd278 100644
--- a/fs/gfs2/trans.c
+++ b/fs/gfs2/trans.c
@@ -50,6 +50,7 @@ int gfs2_trans_begin(struct gfs2_sbd *sdp, unsigned int blocks,
 	if (revokes)
 		tr->tr_reserved += gfs2_struct2blk(sdp, revokes,
 						   sizeof(u64));
+	sb_start_intwrite(sdp->sd_vfs);
 	gfs2_holder_init(sdp->sd_trans_gl, LM_ST_SHARED, 0, &tr->tr_t_gh);
 
 	error = gfs2_glock_nq(&tr->tr_t_gh);
@@ -68,6 +69,7 @@ fail_gunlock:
 	gfs2_glock_dq(&tr->tr_t_gh);
 
 fail_holder_uninit:
+	sb_end_intwrite(sdp->sd_vfs);
 	gfs2_holder_uninit(&tr->tr_t_gh);
 	kfree(tr);
 
@@ -116,6 +118,7 @@ void gfs2_trans_end(struct gfs2_sbd *sdp)
 			gfs2_holder_uninit(&tr->tr_t_gh);
 			kfree(tr);
 		}
+		sb_end_intwrite(sdp->sd_vfs);
 		return;
 	}
 
@@ -136,6 +139,7 @@ void gfs2_trans_end(struct gfs2_sbd *sdp)
 
 	if (sdp->sd_vfs->s_flags & MS_SYNCHRONOUS)
 		gfs2_log_flush(sdp, NULL);
+	sb_end_intwrite(sdp->sd_vfs);
 }
 
 /**
-- 
1.7.1