[PATCH] xfs: fix quota off hang from non-blocking flush

Dave Chinner
2020-07-01T07:51:49Z

From: Dave Chinner <dchinner@redhat.com>

Found by inspection after having xfs/305 hang 1 in ~50 iterations
in a quotaoff operation:

[ 8872.301115] xfs_quota D13888 92262 91813 0x00004002
[ 8872.302538] Call Trace:
[ 8872.303193] __schedule+0x2d2/0x780
[ 8872.304108] ? do_raw_spin_unlock+0x57/0xd0
[ 8872.305198] schedule+0x6e/0xe0
[ 8872.306021] schedule_timeout+0x14d/0x300
[ 8872.307060] ? __next_timer_interrupt+0xe0/0xe0
[ 8872.308231] ? xfs_qm_dqusage_adjust+0x200/0x200
[ 8872.309422] schedule_timeout_uninterruptible+0x2a/0x30
[ 8872.310759] xfs_qm_dquot_walk.isra.0+0x15a/0x1b0
[ 8872.311971] xfs_qm_dqpurge_all+0x7f/0x90
[ 8872.313022] xfs_qm_scall_quotaoff+0x18d/0x2b0
[ 8872.314163] xfs_quota_disable+0x3a/0x60
[ 8872.315179] kernel_quotactl+0x7e2/0x8d0
[ 8872.316196] ? __do_sys_newstat+0x51/0x80
[ 8872.317238] __x64_sys_quotactl+0x1e/0x30
[ 8872.318266] do_syscall_64+0x46/0x90
[ 8872.319193] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 8872.320490] RIP: 0033:0x7f46b5490f2a
[ 8872.321414] Code: Bad RIP value.

Returning -EAGAIN from xfs_qm_dqpurge() without clearing the
XFS_DQ_FREEING flag means the xfs_qm_dqpurge_all() code can never
free the dquot, and we loop forever waiting for the XFS_DQ_FREEING
flag to go away on the dquot that leaked it via -EAGAIN.

Fixes: 8d3d7e2b35ea ("xfs: trylock underlying buffer on dquot flush")
Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
fs/xfs/xfs_qm.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/fs/xfs/xfs_qm.c b/fs/xfs/xfs_qm.c
index d6cd83317344..938023dd8ce5 100644
--- a/fs/xfs/xfs_qm.c
+++ b/fs/xfs/xfs_qm.c
@@ -148,6 +148,7 @@ xfs_qm_dqpurge(
error = xfs_bwrite(bp);
xfs_buf_relse(bp);
} else if (error == -EAGAIN) {
+ dqp->dq_flags &= ~XFS_DQ_FREEING;
goto out_unlock;
}
xfs_dqflock(dqp);
--
2.26.2.761.g0e0b3e54be