[patch 1/2] mm: page_mkwrite change prototype to match fault

[patch 1/2] mm: page_mkwrite change prototype to match fault

[Nick Piggin]

Change the page_mkwrite prototype to take a struct vm_fault, and return
VM_FAULT_xxx flags. Same as ->fault handler. Should be no change in
behaviour.

This makes it possible to return much more detailed error information to
the VM (and also can provide more information eg. virtual_address to the
driver, which might be important in some special cases).

This is required for a subsequent fix. And will also make it easier to
merge page_mkwrite() with fault() in future.

---
 Documentation/filesystems/Locking |    2 +-
 drivers/video/fb_defio.c          |    3 ++-
 fs/btrfs/ctree.h                  |    2 +-
 fs/btrfs/inode.c                  |    5 ++++-
 fs/buffer.c                       |    6 +++++-
 fs/ext4/ext4.h                    |    2 +-
 fs/ext4/inode.c                   |    5 ++++-
 fs/fuse/file.c                    |    3 ++-
 fs/gfs2/ops_file.c                |    5 ++++-
 fs/nfs/file.c                     |    5 ++++-
 fs/ocfs2/mmap.c                   |    6 ++++--
 fs/ubifs/file.c                   |    9 ++++++---
 fs/xfs/linux-2.6/xfs_file.c       |    4 ++--
 include/linux/buffer_head.h       |    2 +-
 include/linux/mm.h                |    3 ++-
 mm/memory.c                       |   25 +++++++++++++++++++++----
 16 files changed, 64 insertions(+), 23 deletions(-)

Index: linux-2.6/Documentation/filesystems/Locking
===================================================================
--- linux-2.6.orig/Documentation/filesystems/Locking
+++ linux-2.6/Documentation/filesystems/Locking
@@ -502,7 +502,7 @@ prototypes:
 	void (*open)(struct vm_area_struct*);
 	void (*close)(struct vm_area_struct*);
 	int (*fault)(struct vm_area_struct*, struct vm_fault *);
-	int (*page_mkwrite)(struct vm_area_struct *, struct page *);
+	int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
 	int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
 
 locking rules:
Index: linux-2.6/fs/btrfs/ctree.h
===================================================================
--- linux-2.6.orig/fs/btrfs/ctree.h
+++ linux-2.6/fs/btrfs/ctree.h
@@ -2051,7 +2051,7 @@ int btrfs_merge_bio_hook(struct page *pa
 unsigned long btrfs_force_ra(struct address_space *mapping,
 			      struct file_ra_state *ra, struct file *file,
 			      pgoff_t offset, pgoff_t last_index);
-int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page);
+int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
 int btrfs_readpage(struct file *file, struct page *page);
 void btrfs_delete_inode(struct inode *inode);
 void btrfs_put_inode(struct inode *inode);
Index: linux-2.6/fs/btrfs/inode.c
===================================================================
--- linux-2.6.orig/fs/btrfs/inode.c
+++ linux-2.6/fs/btrfs/inode.c
@@ -4292,8 +4292,9 @@ static void btrfs_invalidatepage(struct
  * beyond EOF, then the page is guaranteed safe against truncation until we
  * unlock the page.
  */
-int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	struct inode *inode = fdentry(vma->vm_file)->d_inode;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
@@ -4362,6 +4363,8 @@ again:
 out_unlock:
 	unlock_page(page);
 out:
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -2466,9 +2466,10 @@ int block_commit_write(struct page *page
  * unlock the page.
  */
 int
-block_page_mkwrite(struct vm_area_struct *vma, struct page *page,
+block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 		   get_block_t get_block)
 {
+	struct page *page = vmf->page;
 	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
 	unsigned long end;
 	loff_t size;
@@ -2493,6 +2494,9 @@ block_page_mkwrite(struct vm_area_struct
 		ret = block_commit_write(page, 0, end);
 
 out_unlock:
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
+
 	unlock_page(page);
 	return ret;
 }
Index: linux-2.6/fs/ext4/ext4.h
===================================================================
--- linux-2.6.orig/fs/ext4/ext4.h
+++ linux-2.6/fs/ext4/ext4.h
@@ -1097,7 +1097,7 @@ extern int ext4_meta_trans_blocks(struct
 extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
 extern int ext4_block_truncate_page(handle_t *handle,
 		struct address_space *mapping, loff_t from);
-extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page);
+extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
 
 /* ioctl.c */
 extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
Index: linux-2.6/fs/ext4/inode.c
===================================================================
--- linux-2.6.orig/fs/ext4/inode.c
+++ linux-2.6/fs/ext4/inode.c
@@ -5116,8 +5116,9 @@ static int ext4_bh_unmapped(handle_t *ha
 	return !buffer_mapped(bh);
 }
 
-int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	loff_t size;
 	unsigned long len;
 	int ret = -EINVAL;
@@ -5169,6 +5170,8 @@ int ext4_page_mkwrite(struct vm_area_str
 		goto out_unlock;
 	ret = 0;
 out_unlock:
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	up_read(&inode->i_alloc_sem);
 	return ret;
 }
Index: linux-2.6/fs/fuse/file.c
===================================================================
--- linux-2.6.orig/fs/fuse/file.c
+++ linux-2.6/fs/fuse/file.c
@@ -1234,8 +1234,9 @@ static void fuse_vma_close(struct vm_are
  * - sync(2)
  * - try_to_free_pages() with order > PAGE_ALLOC_COSTLY_ORDER
  */
-static int fuse_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int fuse_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	/*
 	 * Don't use page->mapping as it may become NULL from a
 	 * concurrent truncate.
Index: linux-2.6/fs/gfs2/ops_file.c
===================================================================
--- linux-2.6.orig/fs/gfs2/ops_file.c
+++ linux-2.6/fs/gfs2/ops_file.c
@@ -336,8 +336,9 @@ static int gfs2_allocate_page_backing(st
  * blocks allocated on disk to back that page.
  */
 
-static int gfs2_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int gfs2_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;
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_sbd *sdp = GFS2_SB(inode);
@@ -409,6 +410,8 @@ out_unlock:
 	gfs2_glock_dq(&gh);
 out:
 	gfs2_holder_uninit(&gh);
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/nfs/file.c
===================================================================
--- linux-2.6.orig/fs/nfs/file.c
+++ linux-2.6/fs/nfs/file.c
@@ -451,8 +451,9 @@ const struct address_space_operations nf
 	.launder_page = nfs_launder_page,
 };
 
-static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	struct file *filp = vma->vm_file;
 	struct dentry *dentry = filp->f_path.dentry;
 	unsigned pagelen;
@@ -483,6 +484,8 @@ static int nfs_vm_page_mkwrite(struct vm
 		ret = pagelen;
 out_unlock:
 	unlock_page(page);
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/ocfs2/mmap.c
===================================================================
--- linux-2.6.orig/fs/ocfs2/mmap.c
+++ linux-2.6/fs/ocfs2/mmap.c
@@ -154,8 +154,9 @@ out:
 	return ret;
 }
 
-static int ocfs2_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int ocfs2_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;
 	struct buffer_head *di_bh = NULL;
 	sigset_t blocked, oldset;
@@ -196,7 +197,8 @@ out:
 	ret2 = ocfs2_vm_op_unblock_sigs(&oldset);
 	if (ret2 < 0)
 		mlog_errno(ret2);
-
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/ubifs/file.c
===================================================================
--- linux-2.6.orig/fs/ubifs/file.c
+++ linux-2.6/fs/ubifs/file.c
@@ -1434,8 +1434,9 @@ static int ubifs_releasepage(struct page
  * mmap()d file has taken write protection fault and is being made
  * writable. UBIFS must ensure page is budgeted for.
  */
-static int ubifs_vm_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int ubifs_vm_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;
 	struct ubifs_info *c = inode->i_sb->s_fs_info;
 	struct timespec now = ubifs_current_time(inode);
@@ -1447,7 +1448,7 @@ static int ubifs_vm_page_mkwrite(struct
 	ubifs_assert(!(inode->i_sb->s_flags & MS_RDONLY));
 
 	if (unlikely(c->ro_media))
-		return -EROFS;
+		return VM_FAULT_SIGBUS; /* -EROFS */
 
 	/*
 	 * We have not locked @page so far so we may budget for changing the
@@ -1480,7 +1481,7 @@ static int ubifs_vm_page_mkwrite(struct
 		if (err == -ENOSPC)
 			ubifs_warn("out of space for mmapped file "
 				   "(inode number %lu)", inode->i_ino);
-		return err;
+		return VM_FAULT_SIGBUS;
 	}
 
 	lock_page(page);
@@ -1520,6 +1521,8 @@ static int ubifs_vm_page_mkwrite(struct
 out_unlock:
 	unlock_page(page);
 	ubifs_release_budget(c, &req);
+	if (err)
+		err = VM_FAULT_SIGBUS;
 	return err;
 }
 
Index: linux-2.6/fs/xfs/linux-2.6/xfs_file.c
===================================================================
--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_file.c
+++ linux-2.6/fs/xfs/linux-2.6/xfs_file.c
@@ -234,9 +234,9 @@ xfs_file_mmap(
 STATIC int
 xfs_vm_page_mkwrite(
 	struct vm_area_struct	*vma,
-	struct page		*page)
+	struct vm_fault		*vmf)
 {
-	return block_page_mkwrite(vma, page, xfs_get_blocks);
+	return block_page_mkwrite(vma, vmf, xfs_get_blocks);
 }
 
 const struct file_operations xfs_file_operations = {
Index: linux-2.6/include/linux/buffer_head.h
===================================================================
--- linux-2.6.orig/include/linux/buffer_head.h
+++ linux-2.6/include/linux/buffer_head.h
@@ -223,7 +223,7 @@ int cont_write_begin(struct file *, stru
 			get_block_t *, loff_t *);
 int generic_cont_expand_simple(struct inode *inode, loff_t size);
 int block_commit_write(struct page *page, unsigned from, unsigned to);
-int block_page_mkwrite(struct vm_area_struct *vma, struct page *page,
+int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 				get_block_t get_block);
 void block_sync_page(struct page *);
 sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h
+++ linux-2.6/include/linux/mm.h
@@ -134,6 +134,7 @@ extern pgprot_t protection_map[16];
 
 #define FAULT_FLAG_WRITE	0x01	/* Fault was a write access */
 #define FAULT_FLAG_NONLINEAR	0x02	/* Fault was via a nonlinear mapping */
+#define FAULT_FLAG_MKWRITE	0x04	/* Fault was mkwrite of existing pte */
 
 /*
  * This interface is used by x86 PAT code to identify a pfn mapping that is
@@ -186,7 +187,7 @@ struct vm_operations_struct {
 
 	/* notification that a previously read-only page is about to become
 	 * writable, if an error is returned it will cause a SIGBUS */
-	int (*page_mkwrite)(struct vm_area_struct *vma, struct page *page);
+	int (*page_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf);
 
 	/* called by access_process_vm when get_user_pages() fails, typically
 	 * for use by special VMAs that can switch between memory and hardware
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c
+++ linux-2.6/mm/memory.c
@@ -1938,6 +1938,14 @@ static int do_wp_page(struct mm_struct *
 		 * get_user_pages(.write=1, .force=1).
 		 */
 		if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
+			struct vm_fault vmf;
+			int tmp;
+
+			vmf.virtual_address = (void __user *)(address & PAGE_MASK);
+			vmf.pgoff = old_page->index;
+			vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
+			vmf.page = old_page;
+
 			/*
 			 * Notify the address space that the page is about to
 			 * become writable so that it can prohibit this or wait
@@ -1949,8 +1957,12 @@ static int do_wp_page(struct mm_struct *
 			page_cache_get(old_page);
 			pte_unmap_unlock(page_table, ptl);
 
-			if (vma->vm_ops->page_mkwrite(vma, old_page) < 0)
+			tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
+			if (unlikely(tmp &
+					(VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
+				ret = tmp;
 				goto unwritable_page;
+			}
 
 			/*
 			 * Since we dropped the lock we need to revalidate
@@ -2099,7 +2111,7 @@ oom:
 
 unwritable_page:
 	page_cache_release(old_page);
-	return VM_FAULT_SIGBUS;
+	return ret;
 }
 
 /*
@@ -2643,9 +2655,14 @@ static int __do_fault(struct mm_struct *
 			 * to become writable
 			 */
 			if (vma->vm_ops->page_mkwrite) {
+				int tmp;
+
 				unlock_page(page);
-				if (vma->vm_ops->page_mkwrite(vma, page) < 0) {
-					ret = VM_FAULT_SIGBUS;
+				vmf.flags |= FAULT_FLAG_MKWRITE;
+				tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
+				if (unlikely(tmp &
+					  (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
+					ret = tmp;
 					anon = 1; /* no anon but release vmf.page */
 					goto out_unlocked;
 				}
Index: linux-2.6/drivers/video/fb_defio.c
===================================================================
--- linux-2.6.orig/drivers/video/fb_defio.c
+++ linux-2.6/drivers/video/fb_defio.c
@@ -85,8 +85,9 @@ EXPORT_SYMBOL_GPL(fb_deferred_io_fsync);
 
 /* vm_ops->page_mkwrite handler */
 static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
-				  struct page *page)
+				  struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	struct fb_info *info = vma->vm_private_data;
 	struct fb_deferred_io *fbdefio = info->fbdefio;
 	struct page *cur;

[rfc][patch 2/2] buffer, btrfs: fix page_mkwrite error cases

[Nick Piggin]

page_mkwrite is called with neither the page lock nor the ptl held. This
means a page can be concurrently truncated or invalidated out from underneath
it. Callers are supposed to prevent truncate races themselves, however
previously the only thing they can do in case they hit one is to raise a
SIGBUS. A sigbus is wrong for the case that the page has been invalidated
or truncated within i_size (eg. hole punched). Callers may also have to
perform memory allocations in this path, where again, SIGBUS would be wrong.

The previous patch made it possible to properly specify errors. Convert
the generic buffer.c code and btrfs to return sane error values
(in the case of page removed from pagecache, VM_FAULT_NOPAGE will cause the
fault handler to exit without doing anything, and the fault will be retried 
properly).

Should fix all filesystems, but this is just a demonstration/rfc. The
other fses are slightly less trivial :) If anybody cares to fix their
filesystem and send me a patch, that would be nice (but not required,
because patch 1/2 is back compatible).

---
 fs/btrfs/inode.c |   10 ++++++----
 fs/buffer.c      |   12 ++++++++----
 2 files changed, 14 insertions(+), 8 deletions(-)

Index: linux-2.6/fs/btrfs/inode.c
===================================================================
--- linux-2.6.orig/fs/btrfs/inode.c
+++ linux-2.6/fs/btrfs/inode.c
@@ -4307,10 +4307,14 @@ int btrfs_page_mkwrite(struct vm_area_st
 	u64 page_end;
 
 	ret = btrfs_check_data_free_space(root, inode, PAGE_CACHE_SIZE);
-	if (ret)
+	if (ret) {
+		if (ret == -ENOMEM)
+			ret = VM_FAULT_OOM;
+		else /* -ENOSPC, -EIO, etc */
+			ret = VM_FAULT_SIGBUS;
 		goto out;
 
-	ret = -EINVAL;
+	ret = VM_FAULT_NOPAGE; /* make the VM retry the fault */
 again:
 	lock_page(page);
 	size = i_size_read(inode);
@@ -4363,8 +4367,6 @@ again:
 out_unlock:
 	unlock_page(page);
 out:
-	if (ret)
-		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -2473,7 +2473,7 @@ block_page_mkwrite(struct vm_area_struct
 	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
 	unsigned long end;
 	loff_t size;
-	int ret = -EINVAL;
+	int ret = VM_FAULT_NOPAGE; /* make the VM retry the fault */
 
 	lock_page(page);
 	size = i_size_read(inode);
@@ -2493,10 +2493,14 @@ block_page_mkwrite(struct vm_area_struct
 	if (!ret)
 		ret = block_commit_write(page, 0, end);
 
-out_unlock:
-	if (ret)
-		ret = VM_FAULT_SIGBUS;
+	if (unlikely(ret)) {
+		if (ret == -ENOMEM)
+			ret = VM_FAULT_OOM;
+		else /* -ENOSPC, -EIO, etc */
+			ret = VM_FAULT_SIGBUS;
+	}
 
+out_unlock:
 	unlock_page(page);
 	return ret;
 }

Re: [patch 1/2] mm: page_mkwrite change prototype to match fault

[steve]

Hi,

Looks good to me from a GFS2 standpoint,

Steve.

On Tue, Mar 03, 2009 at 11:38:38AM +0100, Nick Piggin wrote:
> 
> Change the page_mkwrite prototype to take a struct vm_fault, and return
> VM_FAULT_xxx flags. Same as ->fault handler. Should be no change in
> behaviour.
> 
> This makes it possible to return much more detailed error information to
> the VM (and also can provide more information eg. virtual_address to the
> driver, which might be important in some special cases).
> 
> This is required for a subsequent fix. And will also make it easier to
> merge page_mkwrite() with fault() in future.
> 
> ---
>  Documentation/filesystems/Locking |    2 +-
>  drivers/video/fb_defio.c          |    3 ++-
>  fs/btrfs/ctree.h                  |    2 +-
>  fs/btrfs/inode.c                  |    5 ++++-
>  fs/buffer.c                       |    6 +++++-
>  fs/ext4/ext4.h                    |    2 +-
>  fs/ext4/inode.c                   |    5 ++++-
>  fs/fuse/file.c                    |    3 ++-
>  fs/gfs2/ops_file.c                |    5 ++++-
>  fs/nfs/file.c                     |    5 ++++-
>  fs/ocfs2/mmap.c                   |    6 ++++--
>  fs/ubifs/file.c                   |    9 ++++++---
>  fs/xfs/linux-2.6/xfs_file.c       |    4 ++--
>  include/linux/buffer_head.h       |    2 +-
>  include/linux/mm.h                |    3 ++-
>  mm/memory.c                       |   25 +++++++++++++++++++++----
>  16 files changed, 64 insertions(+), 23 deletions(-)
> 
> Index: linux-2.6/Documentation/filesystems/Locking
> ===================================================================
> --- linux-2.6.orig/Documentation/filesystems/Locking
> +++ linux-2.6/Documentation/filesystems/Locking
> @@ -502,7 +502,7 @@ prototypes:
>  	void (*open)(struct vm_area_struct*);
>  	void (*close)(struct vm_area_struct*);
>  	int (*fault)(struct vm_area_struct*, struct vm_fault *);
> -	int (*page_mkwrite)(struct vm_area_struct *, struct page *);
> +	int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
>  	int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
>  
>  locking rules:
> Index: linux-2.6/fs/btrfs/ctree.h
> ===================================================================
> --- linux-2.6.orig/fs/btrfs/ctree.h
> +++ linux-2.6/fs/btrfs/ctree.h
> @@ -2051,7 +2051,7 @@ int btrfs_merge_bio_hook(struct page *pa
>  unsigned long btrfs_force_ra(struct address_space *mapping,
>  			      struct file_ra_state *ra, struct file *file,
>  			      pgoff_t offset, pgoff_t last_index);
> -int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page);
> +int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
>  int btrfs_readpage(struct file *file, struct page *page);
>  void btrfs_delete_inode(struct inode *inode);
>  void btrfs_put_inode(struct inode *inode);
> Index: linux-2.6/fs/btrfs/inode.c
> ===================================================================
> --- linux-2.6.orig/fs/btrfs/inode.c
> +++ linux-2.6/fs/btrfs/inode.c
> @@ -4292,8 +4292,9 @@ static void btrfs_invalidatepage(struct
>   * beyond EOF, then the page is guaranteed safe against truncation until we
>   * unlock the page.
>   */
> -int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
> +	struct page *page = vmf->page;
>  	struct inode *inode = fdentry(vma->vm_file)->d_inode;
>  	struct btrfs_root *root = BTRFS_I(inode)->root;
>  	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
> @@ -4362,6 +4363,8 @@ again:
>  out_unlock:
>  	unlock_page(page);
>  out:
> +	if (ret)
> +		ret = VM_FAULT_SIGBUS;
>  	return ret;
>  }
>  
> Index: linux-2.6/fs/buffer.c
> ===================================================================
> --- linux-2.6.orig/fs/buffer.c
> +++ linux-2.6/fs/buffer.c
> @@ -2466,9 +2466,10 @@ int block_commit_write(struct page *page
>   * unlock the page.
>   */
>  int
> -block_page_mkwrite(struct vm_area_struct *vma, struct page *page,
> +block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
>  		   get_block_t get_block)
>  {
> +	struct page *page = vmf->page;
>  	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
>  	unsigned long end;
>  	loff_t size;
> @@ -2493,6 +2494,9 @@ block_page_mkwrite(struct vm_area_struct
>  		ret = block_commit_write(page, 0, end);
>  
>  out_unlock:
> +	if (ret)
> +		ret = VM_FAULT_SIGBUS;
> +
>  	unlock_page(page);
>  	return ret;
>  }
> Index: linux-2.6/fs/ext4/ext4.h
> ===================================================================
> --- linux-2.6.orig/fs/ext4/ext4.h
> +++ linux-2.6/fs/ext4/ext4.h
> @@ -1097,7 +1097,7 @@ extern int ext4_meta_trans_blocks(struct
>  extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
>  extern int ext4_block_truncate_page(handle_t *handle,
>  		struct address_space *mapping, loff_t from);
> -extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page);
> +extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
>  
>  /* ioctl.c */
>  extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
> Index: linux-2.6/fs/ext4/inode.c
> ===================================================================
> --- linux-2.6.orig/fs/ext4/inode.c
> +++ linux-2.6/fs/ext4/inode.c
> @@ -5116,8 +5116,9 @@ static int ext4_bh_unmapped(handle_t *ha
>  	return !buffer_mapped(bh);
>  }
>  
> -int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
> +	struct page *page = vmf->page;
>  	loff_t size;
>  	unsigned long len;
>  	int ret = -EINVAL;
> @@ -5169,6 +5170,8 @@ int ext4_page_mkwrite(struct vm_area_str
>  		goto out_unlock;
>  	ret = 0;
>  out_unlock:
> +	if (ret)
> +		ret = VM_FAULT_SIGBUS;
>  	up_read(&inode->i_alloc_sem);
>  	return ret;
>  }
> Index: linux-2.6/fs/fuse/file.c
> ===================================================================
> --- linux-2.6.orig/fs/fuse/file.c
> +++ linux-2.6/fs/fuse/file.c
> @@ -1234,8 +1234,9 @@ static void fuse_vma_close(struct vm_are
>   * - sync(2)
>   * - try_to_free_pages() with order > PAGE_ALLOC_COSTLY_ORDER
>   */
> -static int fuse_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +static int fuse_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
> +	struct page *page = vmf->page;
>  	/*
>  	 * Don't use page->mapping as it may become NULL from a
>  	 * concurrent truncate.
> Index: linux-2.6/fs/gfs2/ops_file.c
> ===================================================================
> --- linux-2.6.orig/fs/gfs2/ops_file.c
> +++ linux-2.6/fs/gfs2/ops_file.c
> @@ -336,8 +336,9 @@ static int gfs2_allocate_page_backing(st
>   * blocks allocated on disk to back that page.
>   */
>  
> -static int gfs2_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +static int gfs2_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;
>  	struct gfs2_inode *ip = GFS2_I(inode);
>  	struct gfs2_sbd *sdp = GFS2_SB(inode);
> @@ -409,6 +410,8 @@ out_unlock:
>  	gfs2_glock_dq(&gh);
>  out:
>  	gfs2_holder_uninit(&gh);
> +	if (ret)
> +		ret = VM_FAULT_SIGBUS;
>  	return ret;
>  }
>  
> Index: linux-2.6/fs/nfs/file.c
> ===================================================================
> --- linux-2.6.orig/fs/nfs/file.c
> +++ linux-2.6/fs/nfs/file.c
> @@ -451,8 +451,9 @@ const struct address_space_operations nf
>  	.launder_page = nfs_launder_page,
>  };
>  
> -static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
>  {
> +	struct page *page = vmf->page;
>  	struct file *filp = vma->vm_file;
>  	struct dentry *dentry = filp->f_path.dentry;
>  	unsigned pagelen;
> @@ -483,6 +484,8 @@ static int nfs_vm_page_mkwrite(struct vm
>  		ret = pagelen;
>  out_unlock:
>  	unlock_page(page);
> +	if (ret)
> +		ret = VM_FAULT_SIGBUS;
>  	return ret;
>  }
>  
> Index: linux-2.6/fs/ocfs2/mmap.c
> ===================================================================
> --- linux-2.6.orig/fs/ocfs2/mmap.c
> +++ linux-2.6/fs/ocfs2/mmap.c
> @@ -154,8 +154,9 @@ out:
>  	return ret;
>  }
>  
> -static int ocfs2_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +static int ocfs2_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;
>  	struct buffer_head *di_bh = NULL;
>  	sigset_t blocked, oldset;
> @@ -196,7 +197,8 @@ out:
>  	ret2 = ocfs2_vm_op_unblock_sigs(&oldset);
>  	if (ret2 < 0)
>  		mlog_errno(ret2);
> -
> +	if (ret)
> +		ret = VM_FAULT_SIGBUS;
>  	return ret;
>  }
>  
> Index: linux-2.6/fs/ubifs/file.c
> ===================================================================
> --- linux-2.6.orig/fs/ubifs/file.c
> +++ linux-2.6/fs/ubifs/file.c
> @@ -1434,8 +1434,9 @@ static int ubifs_releasepage(struct page
>   * mmap()d file has taken write protection fault and is being made
>   * writable. UBIFS must ensure page is budgeted for.
>   */
> -static int ubifs_vm_page_mkwrite(struct vm_area_struct *vma, struct page *page)
> +static int ubifs_vm_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;
>  	struct ubifs_info *c = inode->i_sb->s_fs_info;
>  	struct timespec now = ubifs_current_time(inode);
> @@ -1447,7 +1448,7 @@ static int ubifs_vm_page_mkwrite(struct
>  	ubifs_assert(!(inode->i_sb->s_flags & MS_RDONLY));
>  
>  	if (unlikely(c->ro_media))
> -		return -EROFS;
> +		return VM_FAULT_SIGBUS; /* -EROFS */
>  
>  	/*
>  	 * We have not locked @page so far so we may budget for changing the
> @@ -1480,7 +1481,7 @@ static int ubifs_vm_page_mkwrite(struct
>  		if (err == -ENOSPC)
>  			ubifs_warn("out of space for mmapped file "
>  				   "(inode number %lu)", inode->i_ino);
> -		return err;
> +		return VM_FAULT_SIGBUS;
>  	}
>  
>  	lock_page(page);
> @@ -1520,6 +1521,8 @@ static int ubifs_vm_page_mkwrite(struct
>  out_unlock:
>  	unlock_page(page);
>  	ubifs_release_budget(c, &req);
> +	if (err)
> +		err = VM_FAULT_SIGBUS;
>  	return err;
>  }
>  
> Index: linux-2.6/fs/xfs/linux-2.6/xfs_file.c
> ===================================================================
> --- linux-2.6.orig/fs/xfs/linux-2.6/xfs_file.c
> +++ linux-2.6/fs/xfs/linux-2.6/xfs_file.c
> @@ -234,9 +234,9 @@ xfs_file_mmap(
>  STATIC int
>  xfs_vm_page_mkwrite(
>  	struct vm_area_struct	*vma,
> -	struct page		*page)
> +	struct vm_fault		*vmf)
>  {
> -	return block_page_mkwrite(vma, page, xfs_get_blocks);
> +	return block_page_mkwrite(vma, vmf, xfs_get_blocks);
>  }
>  
>  const struct file_operations xfs_file_operations = {
> Index: linux-2.6/include/linux/buffer_head.h
> ===================================================================
> --- linux-2.6.orig/include/linux/buffer_head.h
> +++ linux-2.6/include/linux/buffer_head.h
> @@ -223,7 +223,7 @@ int cont_write_begin(struct file *, stru
>  			get_block_t *, loff_t *);
>  int generic_cont_expand_simple(struct inode *inode, loff_t size);
>  int block_commit_write(struct page *page, unsigned from, unsigned to);
> -int block_page_mkwrite(struct vm_area_struct *vma, struct page *page,
> +int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
>  				get_block_t get_block);
>  void block_sync_page(struct page *);
>  sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);
> Index: linux-2.6/include/linux/mm.h
> ===================================================================
> --- linux-2.6.orig/include/linux/mm.h
> +++ linux-2.6/include/linux/mm.h
> @@ -134,6 +134,7 @@ extern pgprot_t protection_map[16];
>  
>  #define FAULT_FLAG_WRITE	0x01	/* Fault was a write access */
>  #define FAULT_FLAG_NONLINEAR	0x02	/* Fault was via a nonlinear mapping */
> +#define FAULT_FLAG_MKWRITE	0x04	/* Fault was mkwrite of existing pte */
>  
>  /*
>   * This interface is used by x86 PAT code to identify a pfn mapping that is
> @@ -186,7 +187,7 @@ struct vm_operations_struct {
>  
>  	/* notification that a previously read-only page is about to become
>  	 * writable, if an error is returned it will cause a SIGBUS */
> -	int (*page_mkwrite)(struct vm_area_struct *vma, struct page *page);
> +	int (*page_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf);
>  
>  	/* called by access_process_vm when get_user_pages() fails, typically
>  	 * for use by special VMAs that can switch between memory and hardware
> Index: linux-2.6/mm/memory.c
> ===================================================================
> --- linux-2.6.orig/mm/memory.c
> +++ linux-2.6/mm/memory.c
> @@ -1938,6 +1938,14 @@ static int do_wp_page(struct mm_struct *
>  		 * get_user_pages(.write=1, .force=1).
>  		 */
>  		if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
> +			struct vm_fault vmf;
> +			int tmp;
> +
> +			vmf.virtual_address = (void __user *)(address & PAGE_MASK);
> +			vmf.pgoff = old_page->index;
> +			vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
> +			vmf.page = old_page;
> +
>  			/*
>  			 * Notify the address space that the page is about to
>  			 * become writable so that it can prohibit this or wait
> @@ -1949,8 +1957,12 @@ static int do_wp_page(struct mm_struct *
>  			page_cache_get(old_page);
>  			pte_unmap_unlock(page_table, ptl);
>  
> -			if (vma->vm_ops->page_mkwrite(vma, old_page) < 0)
> +			tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
> +			if (unlikely(tmp &
> +					(VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
> +				ret = tmp;
>  				goto unwritable_page;
> +			}
>  
>  			/*
>  			 * Since we dropped the lock we need to revalidate
> @@ -2099,7 +2111,7 @@ oom:
>  
>  unwritable_page:
>  	page_cache_release(old_page);
> -	return VM_FAULT_SIGBUS;
> +	return ret;
>  }
>  
>  /*
> @@ -2643,9 +2655,14 @@ static int __do_fault(struct mm_struct *
>  			 * to become writable
>  			 */
>  			if (vma->vm_ops->page_mkwrite) {
> +				int tmp;
> +
>  				unlock_page(page);
> -				if (vma->vm_ops->page_mkwrite(vma, page) < 0) {
> -					ret = VM_FAULT_SIGBUS;
> +				vmf.flags |= FAULT_FLAG_MKWRITE;
> +				tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
> +				if (unlikely(tmp &
> +					  (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
> +					ret = tmp;
>  					anon = 1; /* no anon but release vmf.page */
>  					goto out_unlocked;
>  				}
> Index: linux-2.6/drivers/video/fb_defio.c
> ===================================================================
> --- linux-2.6.orig/drivers/video/fb_defio.c
> +++ linux-2.6/drivers/video/fb_defio.c
> @@ -85,8 +85,9 @@ EXPORT_SYMBOL_GPL(fb_deferred_io_fsync);
>  
>  /* vm_ops->page_mkwrite handler */
>  static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
> -				  struct page *page)
> +				  struct vm_fault *vmf)
>  {
> +	struct page *page = vmf->page;
>  	struct fb_info *info = vma->vm_private_data;
>  	struct fb_deferred_io *fbdefio = info->fbdefio;
>  	struct page *cur;
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
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> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: [rfc][patch 2/2] buffer, btrfs: fix page_mkwrite error cases

[Chris Mason]

On Tue, 2009-03-03 at 11:41 +0100, Nick Piggin wrote:
> page_mkwrite is called with neither the page lock nor the ptl held. This
> means a page can be concurrently truncated or invalidated out from underneath
> it. Callers are supposed to prevent truncate races themselves, however
> previously the only thing they can do in case they hit one is to raise a
> SIGBUS. A sigbus is wrong for the case that the page has been invalidated
> or truncated within i_size (eg. hole punched). Callers may also have to
> perform memory allocations in this path, where again, SIGBUS would be wrong.
> 
> The previous patch made it possible to properly specify errors. Convert
> the generic buffer.c code and btrfs to return sane error values
> (in the case of page removed from pagecache, VM_FAULT_NOPAGE will cause the
> fault handler to exit without doing anything, and the fault will be retried 
> properly).
> 

Thanks Nick.  I think the btrfs patch needs an extra } to compile, but
it looks fine.

-chris

Re: [rfc][patch 2/2] buffer, btrfs: fix page_mkwrite error cases

[Nick Piggin]

On Tue, Mar 03, 2009 at 09:26:03AM -0500, Chris Mason wrote:
> On Tue, 2009-03-03 at 11:41 +0100, Nick Piggin wrote:
> > page_mkwrite is called with neither the page lock nor the ptl held. This
> > means a page can be concurrently truncated or invalidated out from underneath
> > it. Callers are supposed to prevent truncate races themselves, however
> > previously the only thing they can do in case they hit one is to raise a
> > SIGBUS. A sigbus is wrong for the case that the page has been invalidated
> > or truncated within i_size (eg. hole punched). Callers may also have to
> > perform memory allocations in this path, where again, SIGBUS would be wrong.
> > 
> > The previous patch made it possible to properly specify errors. Convert
> > the generic buffer.c code and btrfs to return sane error values
> > (in the case of page removed from pagecache, VM_FAULT_NOPAGE will cause the
> > fault handler to exit without doing anything, and the fault will be retried 
> > properly).
> > 
> 
> Thanks Nick.  I think the btrfs patch needs an extra } to compile, but
> it looks fine.

OK... btrfs is obviously untested :) I just got to btrfs and realised
that probably most of the non-trivial ones will want fs maintainers to
take a look. I *think* the following errors should mostly be right:

!page->mapping ==> VM_FAULT_NOPAGE (just cause the VM to retry the fault)
-ENOMEM ==> VM_FAULT_OOM
any other error ==> VM_FAULT_SIGBUS

But there are a lot of possible error paths in some fs'es...

[ For anyone unclear, SIGBUS is to be used when the physical object under
the virtual mapping is invalid/unavailable, as opposed to SIGSEGV for
when the virtual mapping itself if invalid. Obviously fs is below the
virtual memory layer, so SIGBUS / OOM are the only errors that make sense. ]

Re: [rfc][patch 2/2] buffer, btrfs: fix page_mkwrite error cases

[Chris Mason]

On Tue, 2009-03-03 at 15:41 +0100, Nick Piggin wrote:
> On Tue, Mar 03, 2009 at 09:26:03AM -0500, Chris Mason wrote:
> > On Tue, 2009-03-03 at 11:41 +0100, Nick Piggin wrote:
> > > page_mkwrite is called with neither the page lock nor the ptl held. This
> > > means a page can be concurrently truncated or invalidated out from underneath
> > > it. Callers are supposed to prevent truncate races themselves, however
> > > previously the only thing they can do in case they hit one is to raise a
> > > SIGBUS. A sigbus is wrong for the case that the page has been invalidated
> > > or truncated within i_size (eg. hole punched). Callers may also have to
> > > perform memory allocations in this path, where again, SIGBUS would be wrong.
> > > 
> > > The previous patch made it possible to properly specify errors. Convert
> > > the generic buffer.c code and btrfs to return sane error values
> > > (in the case of page removed from pagecache, VM_FAULT_NOPAGE will cause the
> > > fault handler to exit without doing anything, and the fault will be retried 
> > > properly).
> > > 
> > 
> > Thanks Nick.  I think the btrfs patch needs an extra } to compile, but
> > it looks fine.
> 
> OK... btrfs is obviously untested :) I just got to btrfs and realised
> that probably most of the non-trivial ones will want fs maintainers to
> take a look. I *think* the following errors should mostly be right:
>
> !page->mapping ==> VM_FAULT_NOPAGE (just cause the VM to retry the fault)
> -ENOMEM ==> VM_FAULT_OOM
> any other error ==> VM_FAULT_SIGBUS
> 

It's no problem, the patch made things more clear than it was before.
You can add an sob for me once it compiles ;)

-chris


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Re: [patch 1/2] mm: page_mkwrite change prototype to match fault

[Christoph Hellwig]

On Tue, Mar 03, 2009 at 11:38:38AM +0100, Nick Piggin wrote:
> 
> Change the page_mkwrite prototype to take a struct vm_fault, and return
> VM_FAULT_xxx flags. Same as ->fault handler. Should be no change in
> behaviour.

How about just merging it into ->fault?

> This is required for a subsequent fix. And will also make it easier to
> merge page_mkwrite() with fault() in future.

Ah, I should read until the end :)  Any reason not to do the merge just
yet?

Re: [patch 1/2] mm: page_mkwrite change prototype to match fault

[Nick Piggin]

On Tue, Mar 03, 2009 at 10:58:35AM -0500, Christoph Hellwig wrote:
> On Tue, Mar 03, 2009 at 11:38:38AM +0100, Nick Piggin wrote:
> > 
> > Change the page_mkwrite prototype to take a struct vm_fault, and return
> > VM_FAULT_xxx flags. Same as ->fault handler. Should be no change in
> > behaviour.
> 
> How about just merging it into ->fault?
> 
> > This is required for a subsequent fix. And will also make it easier to
> > merge page_mkwrite() with fault() in future.
> 
> Ah, I should read until the end :)  Any reason not to do the merge just
> yet?

Getting there... after my proposed locking change as well it should
be even another step closer.

The only thing is that we probably need to keep the page_mkwrite callback
in the fs layer, but just move it out of the VM. Because it is hard to
make a generic fault function that does the right page_mkwrite thing
for all filesystems.

But at least pushing it down that step will give better efficiency and
be simpler in the VM. (full page fault today has to lock and unlock the
page 3 times with page_mkwrite, wheras it should go to 2 after my locking
change, and then 1 when page_mkwrite gets merged into fault).

It's coming... just a bit slowly.

[patch 1/2] mm: page_mkwrite change prototype to match fault

[Nick Piggin]

Change the page_mkwrite prototype to take a struct vm_fault, and return
VM_FAULT_xxx flags. There should be no functional change.

This makes it possible to return much more detailed error information to
the VM (and also can provide more information eg. virtual_address to the
driver, which might be important in some special cases).

This is required for a subsequent fix. And will also make it easier to
merge page_mkwrite() with fault() in future.

Signed-off-by: Nick Piggin <npiggin@suse.de>
---
 Documentation/filesystems/Locking |    2 +-
 drivers/video/fb_defio.c          |    3 ++-
 fs/btrfs/ctree.h                  |    2 +-
 fs/btrfs/inode.c                  |    5 ++++-
 fs/buffer.c                       |    6 +++++-
 fs/ext4/ext4.h                    |    2 +-
 fs/ext4/inode.c                   |    5 ++++-
 fs/fuse/file.c                    |    3 ++-
 fs/gfs2/ops_file.c                |    5 ++++-
 fs/nfs/file.c                     |    5 ++++-
 fs/ocfs2/mmap.c                   |    6 ++++--
 fs/ubifs/file.c                   |    9 ++++++---
 fs/xfs/linux-2.6/xfs_file.c       |    4 ++--
 include/linux/buffer_head.h       |    2 +-
 include/linux/mm.h                |    3 ++-
 mm/memory.c                       |   26 ++++++++++++++++++++++----
 16 files changed, 65 insertions(+), 23 deletions(-)

Index: linux-2.6/Documentation/filesystems/Locking
===================================================================
--- linux-2.6.orig/Documentation/filesystems/Locking
+++ linux-2.6/Documentation/filesystems/Locking
@@ -502,7 +502,7 @@ prototypes:
 	void (*open)(struct vm_area_struct*);
 	void (*close)(struct vm_area_struct*);
 	int (*fault)(struct vm_area_struct*, struct vm_fault *);
-	int (*page_mkwrite)(struct vm_area_struct *, struct page *);
+	int (*page_mkwrite)(struct vm_area_struct *, struct vm_fault *);
 	int (*access)(struct vm_area_struct *, unsigned long, void*, int, int);
 
 locking rules:
Index: linux-2.6/fs/btrfs/ctree.h
===================================================================
--- linux-2.6.orig/fs/btrfs/ctree.h
+++ linux-2.6/fs/btrfs/ctree.h
@@ -2051,7 +2051,7 @@ int btrfs_merge_bio_hook(struct page *pa
 unsigned long btrfs_force_ra(struct address_space *mapping,
 			      struct file_ra_state *ra, struct file *file,
 			      pgoff_t offset, pgoff_t last_index);
-int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page);
+int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
 int btrfs_readpage(struct file *file, struct page *page);
 void btrfs_delete_inode(struct inode *inode);
 void btrfs_put_inode(struct inode *inode);
Index: linux-2.6/fs/btrfs/inode.c
===================================================================
--- linux-2.6.orig/fs/btrfs/inode.c
+++ linux-2.6/fs/btrfs/inode.c
@@ -4292,8 +4292,9 @@ static void btrfs_invalidatepage(struct
  * beyond EOF, then the page is guaranteed safe against truncation until we
  * unlock the page.
  */
-int btrfs_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+int btrfs_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	struct inode *inode = fdentry(vma->vm_file)->d_inode;
 	struct btrfs_root *root = BTRFS_I(inode)->root;
 	struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
@@ -4362,6 +4363,8 @@ again:
 out_unlock:
 	unlock_page(page);
 out:
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/buffer.c
===================================================================
--- linux-2.6.orig/fs/buffer.c
+++ linux-2.6/fs/buffer.c
@@ -2466,9 +2466,10 @@ int block_commit_write(struct page *page
  * unlock the page.
  */
 int
-block_page_mkwrite(struct vm_area_struct *vma, struct page *page,
+block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 		   get_block_t get_block)
 {
+	struct page *page = vmf->page;
 	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
 	unsigned long end;
 	loff_t size;
@@ -2493,6 +2494,9 @@ block_page_mkwrite(struct vm_area_struct
 		ret = block_commit_write(page, 0, end);
 
 out_unlock:
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
+
 	unlock_page(page);
 	return ret;
 }
Index: linux-2.6/fs/ext4/ext4.h
===================================================================
--- linux-2.6.orig/fs/ext4/ext4.h
+++ linux-2.6/fs/ext4/ext4.h
@@ -1097,7 +1097,7 @@ extern int ext4_meta_trans_blocks(struct
 extern int ext4_chunk_trans_blocks(struct inode *, int nrblocks);
 extern int ext4_block_truncate_page(handle_t *handle,
 		struct address_space *mapping, loff_t from);
-extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page);
+extern int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
 
 /* ioctl.c */
 extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
Index: linux-2.6/fs/ext4/inode.c
===================================================================
--- linux-2.6.orig/fs/ext4/inode.c
+++ linux-2.6/fs/ext4/inode.c
@@ -5116,8 +5116,9 @@ static int ext4_bh_unmapped(handle_t *ha
 	return !buffer_mapped(bh);
 }
 
-int ext4_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+int ext4_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	loff_t size;
 	unsigned long len;
 	int ret = -EINVAL;
@@ -5169,6 +5170,8 @@ int ext4_page_mkwrite(struct vm_area_str
 		goto out_unlock;
 	ret = 0;
 out_unlock:
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	up_read(&inode->i_alloc_sem);
 	return ret;
 }
Index: linux-2.6/fs/fuse/file.c
===================================================================
--- linux-2.6.orig/fs/fuse/file.c
+++ linux-2.6/fs/fuse/file.c
@@ -1234,8 +1234,9 @@ static void fuse_vma_close(struct vm_are
  * - sync(2)
  * - try_to_free_pages() with order > PAGE_ALLOC_COSTLY_ORDER
  */
-static int fuse_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int fuse_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	/*
 	 * Don't use page->mapping as it may become NULL from a
 	 * concurrent truncate.
Index: linux-2.6/fs/gfs2/ops_file.c
===================================================================
--- linux-2.6.orig/fs/gfs2/ops_file.c
+++ linux-2.6/fs/gfs2/ops_file.c
@@ -336,8 +336,9 @@ static int gfs2_allocate_page_backing(st
  * blocks allocated on disk to back that page.
  */
 
-static int gfs2_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int gfs2_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;
 	struct gfs2_inode *ip = GFS2_I(inode);
 	struct gfs2_sbd *sdp = GFS2_SB(inode);
@@ -409,6 +410,8 @@ out_unlock:
 	gfs2_glock_dq(&gh);
 out:
 	gfs2_holder_uninit(&gh);
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/nfs/file.c
===================================================================
--- linux-2.6.orig/fs/nfs/file.c
+++ linux-2.6/fs/nfs/file.c
@@ -451,8 +451,9 @@ const struct address_space_operations nf
 	.launder_page = nfs_launder_page,
 };
 
-static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int nfs_vm_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	struct file *filp = vma->vm_file;
 	struct dentry *dentry = filp->f_path.dentry;
 	unsigned pagelen;
@@ -483,6 +484,8 @@ static int nfs_vm_page_mkwrite(struct vm
 		ret = pagelen;
 out_unlock:
 	unlock_page(page);
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/ocfs2/mmap.c
===================================================================
--- linux-2.6.orig/fs/ocfs2/mmap.c
+++ linux-2.6/fs/ocfs2/mmap.c
@@ -154,8 +154,9 @@ out:
 	return ret;
 }
 
-static int ocfs2_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int ocfs2_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;
 	struct buffer_head *di_bh = NULL;
 	sigset_t blocked, oldset;
@@ -196,7 +197,8 @@ out:
 	ret2 = ocfs2_vm_op_unblock_sigs(&oldset);
 	if (ret2 < 0)
 		mlog_errno(ret2);
-
+	if (ret)
+		ret = VM_FAULT_SIGBUS;
 	return ret;
 }
 
Index: linux-2.6/fs/ubifs/file.c
===================================================================
--- linux-2.6.orig/fs/ubifs/file.c
+++ linux-2.6/fs/ubifs/file.c
@@ -1434,8 +1434,9 @@ static int ubifs_releasepage(struct page
  * mmap()d file has taken write protection fault and is being made
  * writable. UBIFS must ensure page is budgeted for.
  */
-static int ubifs_vm_page_mkwrite(struct vm_area_struct *vma, struct page *page)
+static int ubifs_vm_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;
 	struct ubifs_info *c = inode->i_sb->s_fs_info;
 	struct timespec now = ubifs_current_time(inode);
@@ -1447,7 +1448,7 @@ static int ubifs_vm_page_mkwrite(struct
 	ubifs_assert(!(inode->i_sb->s_flags & MS_RDONLY));
 
 	if (unlikely(c->ro_media))
-		return -EROFS;
+		return VM_FAULT_SIGBUS; /* -EROFS */
 
 	/*
 	 * We have not locked @page so far so we may budget for changing the
@@ -1480,7 +1481,7 @@ static int ubifs_vm_page_mkwrite(struct
 		if (err == -ENOSPC)
 			ubifs_warn("out of space for mmapped file "
 				   "(inode number %lu)", inode->i_ino);
-		return err;
+		return VM_FAULT_SIGBUS;
 	}
 
 	lock_page(page);
@@ -1520,6 +1521,8 @@ static int ubifs_vm_page_mkwrite(struct
 out_unlock:
 	unlock_page(page);
 	ubifs_release_budget(c, &req);
+	if (err)
+		err = VM_FAULT_SIGBUS;
 	return err;
 }
 
Index: linux-2.6/fs/xfs/linux-2.6/xfs_file.c
===================================================================
--- linux-2.6.orig/fs/xfs/linux-2.6/xfs_file.c
+++ linux-2.6/fs/xfs/linux-2.6/xfs_file.c
@@ -234,9 +234,9 @@ xfs_file_mmap(
 STATIC int
 xfs_vm_page_mkwrite(
 	struct vm_area_struct	*vma,
-	struct page		*page)
+	struct vm_fault		*vmf)
 {
-	return block_page_mkwrite(vma, page, xfs_get_blocks);
+	return block_page_mkwrite(vma, vmf, xfs_get_blocks);
 }
 
 const struct file_operations xfs_file_operations = {
Index: linux-2.6/include/linux/buffer_head.h
===================================================================
--- linux-2.6.orig/include/linux/buffer_head.h
+++ linux-2.6/include/linux/buffer_head.h
@@ -223,7 +223,7 @@ int cont_write_begin(struct file *, stru
 			get_block_t *, loff_t *);
 int generic_cont_expand_simple(struct inode *inode, loff_t size);
 int block_commit_write(struct page *page, unsigned from, unsigned to);
-int block_page_mkwrite(struct vm_area_struct *vma, struct page *page,
+int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 				get_block_t get_block);
 void block_sync_page(struct page *);
 sector_t generic_block_bmap(struct address_space *, sector_t, get_block_t *);
Index: linux-2.6/include/linux/mm.h
===================================================================
--- linux-2.6.orig/include/linux/mm.h
+++ linux-2.6/include/linux/mm.h
@@ -134,6 +134,7 @@ extern pgprot_t protection_map[16];
 
 #define FAULT_FLAG_WRITE	0x01	/* Fault was a write access */
 #define FAULT_FLAG_NONLINEAR	0x02	/* Fault was via a nonlinear mapping */
+#define FAULT_FLAG_MKWRITE	0x04	/* Fault was mkwrite of existing pte */
 
 /*
  * This interface is used by x86 PAT code to identify a pfn mapping that is
@@ -186,7 +187,7 @@ struct vm_operations_struct {
 
 	/* notification that a previously read-only page is about to become
 	 * writable, if an error is returned it will cause a SIGBUS */
-	int (*page_mkwrite)(struct vm_area_struct *vma, struct page *page);
+	int (*page_mkwrite)(struct vm_area_struct *vma, struct vm_fault *vmf);
 
 	/* called by access_process_vm when get_user_pages() fails, typically
 	 * for use by special VMAs that can switch between memory and hardware
Index: linux-2.6/mm/memory.c
===================================================================
--- linux-2.6.orig/mm/memory.c
+++ linux-2.6/mm/memory.c
@@ -1938,6 +1938,15 @@ static int do_wp_page(struct mm_struct *
 		 * get_user_pages(.write=1, .force=1).
 		 */
 		if (vma->vm_ops && vma->vm_ops->page_mkwrite) {
+			struct vm_fault vmf;
+			int tmp;
+
+			vmf.virtual_address = (void __user *)(address &
+								PAGE_MASK);
+			vmf.pgoff = old_page->index;
+			vmf.flags = FAULT_FLAG_WRITE|FAULT_FLAG_MKWRITE;
+			vmf.page = old_page;
+
 			/*
 			 * Notify the address space that the page is about to
 			 * become writable so that it can prohibit this or wait
@@ -1949,8 +1958,12 @@ static int do_wp_page(struct mm_struct *
 			page_cache_get(old_page);
 			pte_unmap_unlock(page_table, ptl);
 
-			if (vma->vm_ops->page_mkwrite(vma, old_page) < 0)
+			tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
+			if (unlikely(tmp &
+					(VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
+				ret = tmp;
 				goto unwritable_page;
+			}
 
 			/*
 			 * Since we dropped the lock we need to revalidate
@@ -2099,7 +2112,7 @@ oom:
 
 unwritable_page:
 	page_cache_release(old_page);
-	return VM_FAULT_SIGBUS;
+	return ret;
 }
 
 /*
@@ -2643,9 +2656,14 @@ static int __do_fault(struct mm_struct *
 			 * to become writable
 			 */
 			if (vma->vm_ops->page_mkwrite) {
+				int tmp;
+
 				unlock_page(page);
-				if (vma->vm_ops->page_mkwrite(vma, page) < 0) {
-					ret = VM_FAULT_SIGBUS;
+				vmf.flags |= FAULT_FLAG_MKWRITE;
+				tmp = vma->vm_ops->page_mkwrite(vma, &vmf);
+				if (unlikely(tmp &
+					  (VM_FAULT_ERROR | VM_FAULT_NOPAGE))) {
+					ret = tmp;
 					anon = 1; /* no anon but release vmf.page */
 					goto out_unlocked;
 				}
Index: linux-2.6/drivers/video/fb_defio.c
===================================================================
--- linux-2.6.orig/drivers/video/fb_defio.c
+++ linux-2.6/drivers/video/fb_defio.c
@@ -85,8 +85,9 @@ EXPORT_SYMBOL_GPL(fb_deferred_io_fsync);
 
 /* vm_ops->page_mkwrite handler */
 static int fb_deferred_io_mkwrite(struct vm_area_struct *vma,
-				  struct page *page)
+				  struct vm_fault *vmf)
 {
+	struct page *page = vmf->page;
 	struct fb_info *info = vma->vm_private_data;
 	struct fb_deferred_io *fbdefio = info->fbdefio;
 	struct page *cur;

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