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Subject[patch 37/60] ext4: fix ext4_free_inode() vs. ext4_claim_inode() race

-stable review patch. If anyone has any objections, please let us know.

------------------
From: Eric Sandeen <sandeen@redhat.com>

(cherry picked from commit 7ce9d5d1f3c8736511daa413c64985a05b2feee3)

I was seeing fsck errors on inode bitmaps after a 4 thread
dbench run on a 4 cpu machine:

Inode bitmap differences: -50736 -(50752--50753) etc...

I believe that this is because ext4_free_inode() uses atomic
bitops, and although ext4_new_inode() *used* to also use atomic
bitops for synchronization, commit
393418676a7602e1d7d3f6e560159c65c8cbd50e changed this to use
the sb_bgl_lock, so that we could also synchronize against
read_inode_bitmap and initialization of uninit inode tables.

However, that change left ext4_free_inode using atomic bitops,
which I think leaves no synchronization between setting &
unsetting bits in the inode table.

The below patch fixes it for me, although I wonder if we're
getting at all heavy-handed with this spinlock...

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
fs/ext4/ialloc.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -188,7 +188,7 @@ void ext4_free_inode (handle_t *handle,
struct ext4_group_desc * gdp;
struct ext4_super_block * es;
struct ext4_sb_info *sbi;
- int fatal = 0, err;
+ int fatal = 0, err, cleared;
ext4_group_t flex_group;

if (atomic_read(&inode->i_count) > 1) {
@@ -242,10 +242,12 @@ void ext4_free_inode (handle_t *handle,
goto error_return;

/* Ok, now we can actually update the inode bitmaps.. */
- if (!ext4_clear_bit_atomic(sb_bgl_lock(sbi, block_group),
- bit, bitmap_bh->b_data))
- ext4_error (sb, "ext4_free_inode",
- "bit already cleared for inode %lu", ino);
+ spin_lock(sb_bgl_lock(sbi, block_group));
+ cleared = ext4_clear_bit(bit, bitmap_bh->b_data);
+ spin_unlock(sb_bgl_lock(sbi, block_group));
+ if (!cleared)
+ ext4_error(sb, "ext4_free_inode",
+ "bit already cleared for inode %lu", ino);
else {
gdp = ext4_get_group_desc (sb, block_group, &bh2);




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