From df8052e7dae00bde6f21b40b6e3e1099770f3afc Mon Sep 17 00:00:00 2001 From: Jie Liu Date: Tue, 26 Nov 2013 21:38:49 +0800 Subject: [PATCH] xfs: fix infinite loop by detaching the group/project hints from user dquot 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: [] schedule+0xad/0xc0 [] schedule_timeout+0x35e/0x3c0 [] ? mark_held_locks+0x176/0x1c0 [] ? call_timer_fn+0x2c0/0x2c0 [] ? xfs_qm_shrink_count+0x30/0x30 [xfs] [] schedule_timeout_uninterruptible+0x26/0x30 [] xfs_qm_dquot_walk+0x235/0x260 [xfs] [] ? xfs_perag_get+0x1d8/0x2d0 [xfs] [] ? xfs_perag_get+0x5/0x2d0 [xfs] [] ? xfs_inode_ag_iterator+0xae/0xf0 [xfs] [] ? xfs_trans_free_dqinfo+0x50/0x50 [xfs] [] ? xfs_inode_ag_iterator+0xcf/0xf0 [xfs] [] xfs_qm_dqpurge_all+0x66/0xb0 [xfs] [] xfs_qm_scall_quotaoff+0x20a/0x5f0 [xfs] [] xfs_fs_set_xstate+0x136/0x180 [xfs] [] do_quotactl+0x53a/0x6b0 [] ? iput+0x5b/0x90 [] SyS_quotactl+0x167/0x1d0 [] ? trace_hardirqs_on_thunk+0x3a/0x3f [] 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. Cc: stable@vger.kernel.org Signed-off-by: Jie Liu Reviewed-by: Dave Chinner Signed-off-by: Ben Myers --- fs/xfs/xfs_qm.c | 71 ++++++++++++++++++++++++++++++++++--------------- 1 file changed, 50 insertions(+), 21 deletions(-) diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c index 588e4909c589..dd88f0e27bd8 100644 --- a/fs/xfs/xfs_qm.c +++ b/fs/xfs/xfs_qm.c @@ -134,8 +134,6 @@ xfs_qm_dqpurge( { struct xfs_mount *mp = dqp->q_mount; struct xfs_quotainfo *qi = mp->m_quotainfo; - struct xfs_dquot *gdqp = NULL; - struct xfs_dquot *pdqp = NULL; xfs_dqlock(dqp); if ((dqp->dq_flags & XFS_DQ_FREEING) || dqp->q_nrefs != 0) { @@ -143,21 +141,6 @@ xfs_qm_dqpurge( return EAGAIN; } - /* - * If this quota has a hint attached, prepare for releasing it now. - */ - gdqp = dqp->q_gdquot; - if (gdqp) { - xfs_dqlock(gdqp); - dqp->q_gdquot = NULL; - } - - pdqp = dqp->q_pdquot; - if (pdqp) { - xfs_dqlock(pdqp); - dqp->q_pdquot = NULL; - } - dqp->dq_flags |= XFS_DQ_FREEING; xfs_dqflock(dqp); @@ -206,11 +189,47 @@ xfs_qm_dqpurge( XFS_STATS_DEC(xs_qm_dquot_unused); 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; + struct xfs_dquot *pdqp = 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; + + pdqp = dqp->q_pdquot; + if (pdqp) + dqp->q_pdquot = NULL; + + xfs_dqunlock(dqp); if (gdqp) - xfs_qm_dqput(gdqp); + xfs_qm_dqrele(gdqp); if (pdqp) - xfs_qm_dqput(pdqp); + xfs_qm_dqrele(pdqp); + + if (flags & XFS_QMOPT_UQUOTA) + return xfs_qm_dqpurge(dqp, NULL); + return 0; } @@ -222,8 +241,18 @@ 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) -- 2.39.5