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xfs: avoid nesting transactions in xfs_qm_scall_setqlim() 

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@gmail.com>
Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Ben Myers <bpm@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
(cherry picked from commit f648167f3ac79018c210112508c732ea9bf67c7b)
This commit is contained in:
Dave Chinner 2013-05-21 18:02:00 +10:00 committed by Ben Myers
parent 7ae077802c
commit 08fb39051f
1 changed files with 26 additions and 20 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

46
fs/xfs/xfs_qm_syscalls.c
View File

@ -489,31 +489,36 @@ xfs_qm_scall_setqlim(
if ((newlim->d_fieldmask & XFS_DQ_MASK) == 0)
return 0;
/*
* 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.
*/
mutex_lock(&q->qi_quotaofflock);
/*
* 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.
*/
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);
goto out_rele;
}
/*
* 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).
*/
mutex_lock(&q->qi_quotaofflock);
/*
* Get the dquot (locked), and join it to the transaction.
* Allocate the dquot if this doesn't exist.
*/
if ((error = xfs_qm_dqget(mp, NULL, id, type, XFS_QMOPT_DQALLOC, &dqp))) {
xfs_trans_cancel(tp, XFS_TRANS_ABORT);
ASSERT(error != ENOENT);
goto out_unlock;
}
xfs_dqlock(dqp);
xfs_trans_dqjoin(tp, dqp);
ddq = &dqp->q_core;
@ -621,9 +626,10 @@ xfs_qm_scall_setqlim(
xfs_trans_log_dquot(tp, dqp);
error = xfs_trans_commit(tp, 0);
xfs_qm_dqrele(dqp);
out_unlock:
out_rele:
xfs_qm_dqrele(dqp);
out_unlock:
mutex_unlock(&q->qi_quotaofflock);
return error;
}