Patchwork ext4: ext4_free_blocks() fix

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Submitter Maxim Patlasov
Date June 10, 2011, 10:07 a.m.
Message ID <1307700474-25743-1-git-send-email-maxim.patlasov@gmail.com>
Download mbox | patch
Permalink /patch/99872/
State Accepted
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Comments

Maxim Patlasov - June 10, 2011, 10:07 a.m.
Existent implementation of ext4_free_blocks() always calls vfs_dq_free_block
This looks quite sensible in the most cases: blocks to be freed are associated
with inode and were accounted in quota and i_blocks some time ago.

However, there is a case when blocks to free were not accounted by the time
calling ext4_free_blocks() yet:

1. delalloc is on, write_begin pre-allocated some space in quota
2. write-back happens, ext4 allocates some blocks in ext4_ext_get_blocks()
3. then ext4_ext_get_blocks() gets an error (e.g.  ENOSPC) from
   ext4_ext_insert_extent() and calls ext4_free_blocks().

In this scenario, ext4_free_blocks() calls vfs_dq_free_block() who, in turn,
decrements i_blocks for blocks which were not accounted yet (due to delalloc)
After clean umount, e2fsck reports something like:

> Inode 21, i_blocks is 5080, should be 5128.  Fix<y>?
because i_blocks was erroneously decremented as explained above.

The patch fixes the problem by passing EXT4_FREE_BLOCKS_SKIP_QUPD flag to
ext4_free_blocks(). This flag forces ext4_free_blocks() to skip
vfs_dq_free_block() call.

Signed-off-by: Maxim Patlasov <maxim.patlasov@gmail.com>
---
 fs/ext4/ext4.h    |    1 +
 fs/ext4/extents.c |    4 +++-
 fs/ext4/mballoc.c |    2 +-
 3 files changed, 5 insertions(+), 2 deletions(-)
Maxim Patlasov - June 10, 2011, 10:17 a.m.
I apologise for flooding, patch description in former email was for
slightly different kernel version. Correct description is below:

Existent implementation of ext4_free_blocks() always calls dquot_free_block
This looks quite sensible in the most cases: blocks to be freed are associated
with inode and were accounted in quota and i_blocks some time ago.

However, there is a case when blocks to free were not accounted by the time
calling ext4_free_blocks() yet:

1. delalloc is on, write_begin pre-allocated some space in quota
2. write-back happens, ext4 allocates some blocks in ext4_ext_map_blocks()
3. then ext4_ext_map_blocks() gets an error (e.g.  ENOSPC) from
   ext4_ext_insert_extent() and calls ext4_free_blocks().

In this scenario, ext4_free_blocks() calls dquot_free_block() who, in turn,
decrements i_blocks for blocks which were not accounted yet (due to delalloc)
After clean umount, e2fsck reports something like:

> Inode 21, i_blocks is 5080, should be 5128.  Fix<y>?
because i_blocks was erroneously decremented as explained above.

The patch fixes the problem by passing EXT4_FREE_BLOCKS_SKIP_QUPD flag to
ext4_free_blocks(). This flag forces ext4_free_blocks() to skip
dquot_free_block() call.

Signed-off-by: Maxim Patlasov <maxim.patlasov@gmail.com>

On Fri, Jun 10, 2011 at 2:07 PM, Maxim Patlasov
<maxim.patlasov@gmail.com> wrote:
> Existent implementation of ext4_free_blocks() always calls vfs_dq_free_block
> This looks quite sensible in the most cases: blocks to be freed are associated
> with inode and were accounted in quota and i_blocks some time ago.
>
> However, there is a case when blocks to free were not accounted by the time
> calling ext4_free_blocks() yet:
>
> 1. delalloc is on, write_begin pre-allocated some space in quota
> 2. write-back happens, ext4 allocates some blocks in ext4_ext_get_blocks()
> 3. then ext4_ext_get_blocks() gets an error (e.g.  ENOSPC) from
>   ext4_ext_insert_extent() and calls ext4_free_blocks().
>
> In this scenario, ext4_free_blocks() calls vfs_dq_free_block() who, in turn,
> decrements i_blocks for blocks which were not accounted yet (due to delalloc)
> After clean umount, e2fsck reports something like:
>
>> Inode 21, i_blocks is 5080, should be 5128.  Fix<y>?
> because i_blocks was erroneously decremented as explained above.
>
> The patch fixes the problem by passing EXT4_FREE_BLOCKS_SKIP_QUPD flag to
> ext4_free_blocks(). This flag forces ext4_free_blocks() to skip
> vfs_dq_free_block() call.
>
> Signed-off-by: Maxim Patlasov <maxim.patlasov@gmail.com>
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Theodore Ts'o - July 10, 2011, 11:39 p.m.
Applied to the ext4 tree, with the following changes:

1)  I made the one-line summary clearer:

    ext4: fix i_blocks/quota accounting when extent insertion fails

2) I used the flag name EXT4_FREE_BLOCKS_NO_QUOT_UPDATE which was
clearer than "..._SKIP_QUPD".

Apologies for the delay in getting back to you, and thanks for the
patch.

	      	  	   	   	   - Ted

On Fri, Jun 10, 2011 at 02:17:30PM +0400, Maxim Patlasov wrote:
> I apologise for flooding, patch description in former email was for
> slightly different kernel version. Correct description is below:
> 
> Existent implementation of ext4_free_blocks() always calls dquot_free_block
> This looks quite sensible in the most cases: blocks to be freed are associated
> with inode and were accounted in quota and i_blocks some time ago.
> 
> However, there is a case when blocks to free were not accounted by the time
> calling ext4_free_blocks() yet:
> 
> 1. delalloc is on, write_begin pre-allocated some space in quota
> 2. write-back happens, ext4 allocates some blocks in ext4_ext_map_blocks()
> 3. then ext4_ext_map_blocks() gets an error (e.g.  ENOSPC) from
>    ext4_ext_insert_extent() and calls ext4_free_blocks().
> 
> In this scenario, ext4_free_blocks() calls dquot_free_block() who, in turn,
> decrements i_blocks for blocks which were not accounted yet (due to delalloc)
> After clean umount, e2fsck reports something like:
> 
> > Inode 21, i_blocks is 5080, should be 5128.  Fix<y>?
> because i_blocks was erroneously decremented as explained above.
> 
> The patch fixes the problem by passing EXT4_FREE_BLOCKS_SKIP_QUPD flag to
> ext4_free_blocks(). This flag forces ext4_free_blocks() to skip
> dquot_free_block() call.
> 
> Signed-off-by: Maxim Patlasov <maxim.patlasov@gmail.com>
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Patch

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 1921392..2cff50c 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -526,6 +526,7 @@  struct ext4_new_group_data {
 #define EXT4_FREE_BLOCKS_METADATA	0x0001
 #define EXT4_FREE_BLOCKS_FORGET		0x0002
 #define EXT4_FREE_BLOCKS_VALIDATED	0x0004
+#define EXT4_FREE_BLOCKS_SKIP_QUPD	0x0008
 
 /*
  * ioctl commands
diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 5199bac..4d17497 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3601,12 +3601,14 @@  int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
 
 	err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
 	if (err) {
+		int fb_flags = flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE ?
+			EXT4_FREE_BLOCKS_SKIP_QUPD : 0;
 		/* free data blocks we just allocated */
 		/* not a good idea to call discard here directly,
 		 * but otherwise we'd need to call it every free() */
 		ext4_discard_preallocations(inode);
 		ext4_free_blocks(handle, inode, NULL, ext4_ext_pblock(&newex),
-				 ext4_ext_get_actual_len(&newex), 0);
+				 ext4_ext_get_actual_len(&newex), fb_flags);
 		goto out2;
 	}
 
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 859f2ae..ba391c6 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -4637,7 +4637,7 @@  do_more:
 	}
 	ext4_mark_super_dirty(sb);
 error_return:
-	if (freed)
+	if (freed && !(flags & EXT4_FREE_BLOCKS_SKIP_QUPD))
 		dquot_free_block(inode, freed);
 	brelse(bitmap_bh);
 	ext4_std_error(sb, err);