Currently while doing block allocation grp->bb_free may be getting
modified if discard is happening in parallel.
For e.g. consider a case where there are lot of threads who have
preallocated lot of blocks and there is a thread which is trying
to discard all of this group's PA. Now it could happen that
we see all of those group's bb_free is zero and fail the allocation
while there is sufficient space if we free up all the PA.
So this patch takes the ext4_lock_group() around calculations involving
grp->bb_free in ext4_mb_good_group() & ext4_mb_good_group_nolock()
Signed-off-by: Ritesh Harjani <riteshh@xxxxxxxxxxxxx>
---
fs/ext4/mballoc.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index da11a4a738bd..dcd05ff7c012 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2138,9 +2138,11 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
ext4_group_t group, int cr)
{
struct ext4_group_info *grp = ext4_get_group_info(ac->ac_sb, group);
+ struct super_block *sb = ac->ac_sb;
ext4_grpblk_t free;
int ret = 0;
+ ext4_lock_group(sb, group);
free = grp->bb_free;
if (free == 0)
goto out;
@@ -2148,6 +2150,7 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
goto out;
if (unlikely(EXT4_MB_GRP_BBITMAP_CORRUPT(grp)))
goto out;
+ ext4_unlock_group(sb, group);
/* We only do this if the grp has never been initialized */
if (unlikely(EXT4_MB_GRP_NEED_INIT(grp))) {
@@ -2156,8 +2159,10 @@ static int ext4_mb_good_group_nolock(struct ext4_allocation_context *ac,
return ret;
}
+ ext4_lock_group(sb, group);
ret = ext4_mb_good_group(ac, group, cr);
out:
+ ext4_unlock_group(sb, group);
return ret;
}
--
2.21.0
