Re: [PATCH] btrfs: qgroup: Fix a regression in qgroup reserved space.

[Chris Mason]

On Thu, Aug 06, 2015 at 04:42:41PM +0800, Qu Wenruo wrote:
 Hi Chris,
 
 Would you please consider including this patch into v4.2 if it is still
 possible?
 
 Although the fix is still not perfect and just a hotfix, as qgroup reserve
 parts still have a lot of problems from design and a lot of operations can
 still cause reserve space leak.
 
 But considering how easy it is to trigger, I still hope it to be merged asap
 before 4.2.

Thanks Qu, I'll get this in.

-chris
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[PATCH] btrfs: qgroup: Fix a regression in qgroup reserved space.

[Qu Wenruo]

During the change to new btrfs extent-oriented qgroup implement, due to
it doesn't use the old __qgroup_excl_accounting() for exclusive extent,
it didn't free the reserved bytes.

The bug will cause limit function go crazy as the reserved space is
never freed, increasing limit will have no effect and still cause
EQOUT.

The fix is easy, just free reserved bytes for newly created exclusive
extent as what it does before.

Reported-by: Tsutomu Itoh t-i...@jp.fujitsu.com
Signed-off-by: Yang Dongsheng yangds.f...@cn.fujitsu.com
Signed-off-by: Qu Wenruo quwen...@cn.fujitsu.com
---
To Chris:

Would you please consider merging this patch in the late v4.2 merge
window?
As it's a huge regression and the fix is small enough and just does
what it did before in __qgroup_excl_accounting() function.

The corresponding test case will follow soon.

And sorry for the regression I introduced.

Thanks,
Qu
---
 fs/btrfs/qgroup.c | 5 +
 1 file changed, 5 insertions(+)

diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
index d5f1f03..1667567 100644
--- a/fs/btrfs/qgroup.c
+++ b/fs/btrfs/qgroup.c
@@ -1618,6 +1618,11 @@ static int qgroup_update_counters(struct btrfs_fs_info 
*fs_info,
/* Exclusive - exclusive, nothing changed */
}
}
+
+   /* For exclusive extent, free its reserved bytes too */
+   if (nr_old_roots == 0  nr_new_roots == 1 
+   cur_new_count == nr_new_roots)
+   qg-reserved -= num_bytes;
if (dirty)
qgroup_dirty(fs_info, qg);
}
-- 
2.5.0

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