On Wed, May 08, 2013 at 10:24:25PM -0400, Michael L. Semon wrote:
> Hi! I'm trying to come up with a series of ramblings that may or
> may not be useful in a mailing-list context, with the idea that one
> bug report might be good, the next might be me thinking aloud with
> data in hand because I know something's wrong but can't put my
> finger on it. An ex-girlfriend saw the movie "Rain Man" years ago
> pointed to the screen and said, "Do you see that guy? That's you!"
> If only I could be so smart...or act as well as Dustin Hoffman. The
> noisy thinking is there, just not the brilliant insights...
>
> This report is to pass on a kernel lock detector message that might
> be reproducible under a certain family of tests. generic/230 may
> not be at fault, it's just where the detector went off.
No, there's definitely a bug there. Thanks for the report, Michael.
Try the patch below.
Cheers,
Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
xfs: avoid nesting transactions in xfs_qm_scall_setqlim()
From: Dave Chinner <dchinner@xxxxxxxxxx>
Lockdep reports:
=============================================
[ INFO: possible recursive locking detected ]
3.9.0+ #3 Not tainted
---------------------------------------------
setquota/28368 is trying to acquire lock:
(sb_internal){++++.?}, at: [<c11e8846>] xfs_trans_alloc+0x26/0x50
but task is already holding lock:
(sb_internal){++++.?}, at: [<c11e8846>] xfs_trans_alloc+0x26/0x50
from xfs_qm_scall_setqlim()->xfs_dqread() when a dquot needs to be
allocated.
xfs_qm_scall_setqlim() is starting a transaction and then not
passing it into xfs_qm_dqet() and so it starts it's own transaction
when allocating the dquot. Splat!
Fix this by not allocating the dquot in xfs_qm_scall_setqlim()
inside the setqlim transaction. This requires getting the dquot
first (and allocating it if necessary) then dropping and relocking
the dquot before joining it to the setqlim transaction.
Reported-by: Michael L. Semon <mlsemon35@xxxxxxxxx>
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
fs/xfs/xfs_qm_syscalls.c | 35 ++++++++++++++++++++---------------
1 file changed, 20 insertions(+), 15 deletions(-)
diff --git a/fs/xfs/xfs_qm_syscalls.c b/fs/xfs/xfs_qm_syscalls.c
index c41190c..7e67a3a 100644
--- a/fs/xfs/xfs_qm_syscalls.c
+++ b/fs/xfs/xfs_qm_syscalls.c
@@ -489,31 +489,36 @@ xfs_qm_scall_setqlim(
if ((newlim->d_fieldmask & XFS_DQ_MASK) == 0)
return 0;
- tp = xfs_trans_alloc(mp, XFS_TRANS_QM_SETQLIM);
- error = xfs_trans_reserve(tp, 0, XFS_QM_SETQLIM_LOG_RES(mp),
- 0, 0, XFS_DEFAULT_LOG_COUNT);
- if (error) {
- xfs_trans_cancel(tp, 0);
- return (error);
- }
-
/*
* We don't want to race with a quotaoff so take the quotaoff lock.
- * (We don't hold an inode lock, so there's nothing else to stop
- * a quotaoff from happening). (XXXThis doesn't currently happen
- * because we take the vfslock before calling xfs_qm_sysent).
+ * We don't hold an inode lock, so there's nothing else to stop
+ * a quotaoff from happening.
*/
mutex_lock(&q->qi_quotaofflock);
/*
- * Get the dquot (locked), and join it to the transaction.
- * Allocate the dquot if this doesn't exist.
+ * Get the dquot (locked) before we start, as we need to do a
+ * transaction to allocate it if it doesn't exist. Once we have the
+ * dquot, unlock it so we can start the next transaction safely. We hold
+ * a reference to the dquot, so it's safe to do this unlock/lock without
+ * it being reclaimed in the mean time.
*/
- if ((error = xfs_qm_dqget(mp, NULL, id, type, XFS_QMOPT_DQALLOC, &dqp))) {
- xfs_trans_cancel(tp, XFS_TRANS_ABORT);
+ error = xfs_qm_dqget(mp, NULL, id, type, XFS_QMOPT_DQALLOC, &dqp);
+ if (error) {
ASSERT(error != ENOENT);
goto out_unlock;
}
+ xfs_dqunlock(dqp);
+
+ tp = xfs_trans_alloc(mp, XFS_TRANS_QM_SETQLIM);
+ error = xfs_trans_reserve(tp, 0, XFS_QM_SETQLIM_LOG_RES(mp),
+ 0, 0, XFS_DEFAULT_LOG_COUNT);
+ if (error) {
+ xfs_trans_cancel(tp, 0);
+ return (error);
+ }
+
+ xfs_dqlock(dqp);
xfs_trans_dqjoin(tp, dqp);
ddq = &dqp->q_core;
_______________________________________________
xfs mailing list
xfs@xxxxxxxxxxx
http://oss.sgi.com/mailman/listinfo/xfs
