[3.8.y.z extended stable] Patch "xfs: fix infinite loop by detaching the group/project hints from user" has been added to staging queue
Kamal Mostafa
kamal at canonical.com
Thu Jan 9 23:18:14 UTC 2014
This is a note to let you know that I have just added a patch titled
xfs: fix infinite loop by detaching the group/project hints from user
to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree
which can be found at:
http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue
This patch is scheduled to be released in version 3.8.13.16.
If you, or anyone else, feels it should not be added to this tree, please
reply to this email.
For more information about the 3.8.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable
Thanks.
-Kamal
------
>From 572bf013172952cbba1b96f44d1e5a146e2868cf Mon Sep 17 00:00:00 2001
From: Jie Liu <jeff.liu at oracle.com>
Date: Tue, 26 Nov 2013 21:38:49 +0800
Subject: xfs: fix infinite loop by detaching the group/project hints from user
dquot
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 at oracle.com>
Reviewed-by: Dave Chinner <dchinner at redhat.com>
Signed-off-by: Ben Myers <bpm at sgi.com>
[ kamal: backport to 3.8 (no q_pdquot member, just q_gdquot) ]
Signed-off-by: Kamal Mostafa <kamal at 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
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