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Subject[070/102] ext4: fix i_blocks/quota accounting when extent insertion fails
3.0-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Maxim Patlasov <maxim.patlasov@gmail.com>

commit 7132de744ba76930d13033061018ddd7e3e8cd91 upstream.

The current 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 the new flag
EXT4_FREE_BLOCKS_NO_QUOT_UPDATE to ext4_free_blocks(), to request
that the dquot_free_block() call be skipped.

Signed-off-by: Maxim Patlasov <maxim.patlasov@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/ext4/ext4.h | 1 +
fs/ext4/extents.c | 4 +++-
fs/ext4/mballoc.c | 2 +-
3 files changed, 5 insertions(+), 2 deletions(-)
--- 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_NO_QUOT_UPDATE 0x0008

/*
* ioctl commands
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -3601,12 +3601,14 @@ int ext4_ext_map_blocks(handle_t *handle

err = ext4_ext_insert_extent(handle, inode, path, &newex, flags);
if (err) {
+ int fb_flags = flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE ?
+ EXT4_FREE_BLOCKS_NO_QUOT_UPDATE : 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;
}

--- 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_NO_QUOT_UPDATE))
dquot_free_block(inode, freed);
brelse(bitmap_bh);
ext4_std_error(sb, err);



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