[PATCH 3.8 076/166] xfs: fix infinite loop by detaching the group/project hints from user dquot

Kamal Mostafa
2014-01-15T21:51:30Z

From: Jie Liu <jeff.liu@oracle.com>

commit 718cc6f88cbfc4fbd39609f28c4c86883945f90d upstream.

xfs_quota(8) will hang up if trying to turn group/project quota off
before the user quota is off, this could be 100% reproduced by:
# mount -ouquota,gquota /dev/sda7 /xfs
# mkdir /xfs/test
# xfs_quota -xc 'off -g' /xfs <-- hangs up
# echo w > /proc/sysrq-trigger
# dmesg

SysRq : Show Blocked State
task PC stack pid father
xfs_quota D 0000000000000000 0 27574 2551 0x00000000
[snip]
Call Trace:
[<ffffffff81aaa21d>] schedule+0xad/0xc0
[<ffffffff81aa327e>] schedule_timeout+0x35e/0x3c0
[<ffffffff8114b506>] ? mark_held_locks+0x176/0x1c0
[<ffffffff810ad6c0>] ? call_timer_fn+0x2c0/0x2c0
[<ffffffffa0c25380>] ? xfs_qm_shrink_count+0x30/0x30 [xfs]
[<ffffffff81aa3306>] schedule_timeout_uninterruptible+0x26/0x30
[<ffffffffa0c26155>] xfs_qm_dquot_walk+0x235/0x260 [xfs]
[<ffffffffa0c059d8>] ? xfs_perag_get+0x1d8/0x2d0 [xfs]
[<ffffffffa0c05805>] ? xfs_perag_get+0x5/0x2d0 [xfs]
[<ffffffffa0b7707e>] ? xfs_inode_ag_iterator+0xae/0xf0 [xfs]
[<ffffffffa0c22280>] ? xfs_trans_free_dqinfo+0x50/0x50 [xfs]
[<ffffffffa0b7709f>] ? xfs_inode_ag_iterator+0xcf/0xf0 [xfs]
[<ffffffffa0c261e6>] xfs_qm_dqpurge_all+0x66/0xb0 [xfs]
[<ffffffffa0c2497a>] xfs_qm_scall_quotaoff+0x20a/0x5f0 [xfs]
[<ffffffffa0c2b8f6>] xfs_fs_set_xstate+0x136/0x180 [xfs]
[<ffffffff8136cf7a>] do_quotactl+0x53a/0x6b0
[<ffffffff812fba4b>] ? iput+0x5b/0x90
[<ffffffff8136d257>] SyS_quotactl+0x167/0x1d0
[<ffffffff814cf2ee>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[<ffffffff81abcd19>] system_call_fastpath+0x16/0x1b

It's fine if we turn user quota off at first, then turn off other
kind of quotas if they are enabled since the group/project dquot
refcount is decreased to zero once the user quota if off. Otherwise,
those dquots refcount is non-zero due to the user dquot might refer
to them as hint(s). Hence, above operation cause an infinite loop
at xfs_qm_dquot_walk() while trying to purge dquot cache.

This problem has been around since Linux 3.4, it was introduced by:
[ b84a3a9675 xfs: remove the per-filesystem list of dquots ]

Originally we will release the group dquot pointers because the user
dquots maybe carrying around as a hint via xfs_qm_detach_gdquots().
However, with above change, there is no such work to be done before
purging group/project dquot cache.

In order to solve this problem, this patch introduces a special routine
xfs_qm_dqpurge_hints(), and it would release the group/project dquot
pointers the user dquots maybe carrying around as a hint, and then it
will proceed to purge the user dquot cache if requested.

Signed-off-by: Jie Liu <jeff.liu@oracle.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
[ kamal: backport to 3.8 (no q_pdquot member, just q_gdquot) ]
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
---
fs/xfs/xfs_qm.c | 58 +++++++++++++++++++++++++++++++++++++++++++--------------
1 file changed, 44 insertions(+), 14 deletions(-)

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index 60eff47..e2db199 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -135,7 +135,6 @@ xfs_qm_dqpurge(
{
struct xfs_mount *mp = dqp->q_mount;
struct xfs_quotainfo *qi = mp->m_quotainfo;
- struct xfs_dquot *gdqp = NULL;

xfs_dqlock(dqp);
if ((dqp->dq_flags & XFS_DQ_FREEING) || dqp->q_nrefs != 0) {
@@ -143,16 +142,6 @@ xfs_qm_dqpurge(
return EAGAIN;
}

- /*
- * If this quota has a group hint attached, prepare for releasing it
- * now.
- */
- gdqp = dqp->q_gdquot;
- if (gdqp) {
- xfs_dqlock(gdqp);
- dqp->q_gdquot = NULL;
- }
-
dqp->dq_flags |= XFS_DQ_FREEING;

xfs_dqflock(dqp);
@@ -204,9 +193,40 @@ xfs_qm_dqpurge(
mutex_unlock(&qi->qi_lru_lock);

xfs_qm_dqdestroy(dqp);
+ return 0;
+}
+
+/*
+ * Release the group or project dquot pointers the user dquots maybe carrying
+ * around as a hint, and proceed to purge the user dquot cache if requested.
+*/
+STATIC int
+xfs_qm_dqpurge_hints(
+ struct xfs_dquot *dqp,
+ void *data)
+{
+ struct xfs_dquot *gdqp = NULL;
+ uint flags = *((uint *)data);
+
+ xfs_dqlock(dqp);
+ if (dqp->dq_flags & XFS_DQ_FREEING) {
+ xfs_dqunlock(dqp);
+ return EAGAIN;
+ }
+
+ /* If this quota has a hint attached, prepare for releasing it now */
+ gdqp = dqp->q_gdquot;
+ if (gdqp)
+ dqp->q_gdquot = NULL;
+
+ xfs_dqunlock(dqp);

if (gdqp)
- xfs_qm_dqput(gdqp);
+ xfs_qm_dqrele(gdqp);
+
+ if (flags & XFS_QMOPT_UQUOTA)
+ return xfs_qm_dqpurge(dqp, NULL);
+
return 0;
}

@@ -218,8 +238,18 @@ xfs_qm_dqpurge_all(
struct xfs_mount *mp,
uint flags)
{
- if (flags & XFS_QMOPT_UQUOTA)
- xfs_qm_dquot_walk(mp, XFS_DQ_USER, xfs_qm_dqpurge, NULL);
+ /*
+ * We have to release group/project dquot hint(s) from the user dquot
+ * at first if they are there, otherwise we would run into an infinite
+ * loop while walking through radix tree to purge other type of dquots
+ * since their refcount is not zero if the user dquot refers to them
+ * as hint.
+ *
+ * Call the special xfs_qm_dqpurge_hints() will end up go through the
+ * general xfs_qm_dqpurge() against user dquot cache if requested.
+ */
+ xfs_qm_dquot_walk(mp, XFS_DQ_USER, xfs_qm_dqpurge_hints, &flags);
+
if (flags & XFS_QMOPT_GQUOTA)
xfs_qm_dquot_walk(mp, XFS_DQ_GROUP, xfs_qm_dqpurge, NULL);
if (flags & XFS_QMOPT_PQUOTA)
--
1.8.3.2