[3.0-stable PATCH 27/36] xfs: protect xfs_sync_worker with s_umount semaphore

Mark Tinguely
2012-12-03T23:40:43Z

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From: Ben Myers <bpm@sgi.com>

Upstream commit: 1307bbd2af67283131728637e9489002adb26f10

xfs_sync_worker checks the MS_ACTIVE flag in s_flags to avoid doing
work during mount and unmount. This flag can be cleared by unmount
after the xfs_sync_worker checks it but before the work is completed.
The has caused crashes in the completion handler for the dummy
transaction commited by xfs_sync_worker:

PID: 27544 TASK: ffff88013544e040 CPU: 3 COMMAND: "kworker/3:0"
#0 [ffff88016fdff930] machine_kexec at ffffffff810244e9
#1 [ffff88016fdff9a0] crash_kexec at ffffffff8108d053
#2 [ffff88016fdffa70] oops_end at ffffffff813ad1b8
#3 [ffff88016fdffaa0] no_context at ffffffff8102bd48
#4 [ffff88016fdffaf0] __bad_area_nosemaphore at ffffffff8102c04d
#5 [ffff88016fdffb40] bad_area_nosemaphore at ffffffff8102c12e
#6 [ffff88016fdffb50] do_page_fault at ffffffff813afaee
#7 [ffff88016fdffc60] page_fault at ffffffff813ac635
[exception RIP: xlog_get_lowest_lsn+0x30]
RIP: ffffffffa04a9910 RSP: ffff88016fdffd10 RFLAGS: 00010246
RAX: ffffc90014e48000 RBX: ffff88014d879980 RCX: ffff88014d879980
RDX: ffff8802214ee4c0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffff88016fdffd10 R8: ffff88014d879a80 R9: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: ffff8802214ee400
R13: ffff88014d879980 R14: 0000000000000000 R15: ffff88022fd96605
ORIG_RAX: ffffffffffffffff CS: 0010 SS: 0018
#8 [ffff88016fdffd18] xlog_state_do_callback at ffffffffa04aa186 [xfs]
#9 [ffff88016fdffd98] xlog_state_done_syncing at ffffffffa04aa568 [xfs]

Protect xfs_sync_worker by using the s_umount semaphore at the read
level to provide exclusion with unmount while work is progressing.

Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Signed-off-by: Ben Myers <bpm@sgi.com>
---
fs/xfs/linux-2.6/xfs_sync.c | 29 ++++++++++++++++-------------
1 file changed, 16 insertions(+), 13 deletions(-)

Index: b/fs/xfs/linux-2.6/xfs_sync.c
===================================================================
--- a/fs/xfs/linux-2.6/xfs_sync.c
+++ b/fs/xfs/linux-2.6/xfs_sync.c
@@ -506,21 +506,24 @@ xfs_sync_worker(
* We shouldn't write/force the log if we are in the mount/unmount
* process or on a read only filesystem. The workqueue still needs to be
* active in both cases, however, because it is used for inode reclaim
- * during these times. hence use the MS_ACTIVE flag to avoid doing
- * anything in these periods.
+ * during these times. Use the s_umount semaphore to provide exclusion
+ * with unmount.
*/
- if (!(mp->m_super->s_flags & MS_ACTIVE) &&
- !(mp->m_flags & XFS_MOUNT_RDONLY)) {
- /* dgc: errors ignored here */
- if (mp->m_super->s_frozen == SB_UNFROZEN &&
- xfs_log_need_covered(mp))
- error = xfs_fs_log_dummy(mp);
- else
- xfs_log_force(mp, 0);
- error = xfs_qm_sync(mp, SYNC_TRYLOCK);
+ if (down_read_trylock(&mp->m_super->s_umount)) {
+ if (!(mp->m_super->s_flags & MS_ACTIVE) &&
+ !(mp->m_flags & XFS_MOUNT_RDONLY)) {
+ /* dgc: errors ignored here */
+ if (mp->m_super->s_frozen == SB_UNFROZEN &&
+ xfs_log_need_covered(mp))
+ error = xfs_fs_log_dummy(mp);
+ else
+ xfs_log_force(mp, 0);
+ error = xfs_qm_sync(mp, SYNC_TRYLOCK);

- /* start pushing all the metadata that is currently dirty */
- xfs_ail_push_all(mp->m_ail);
+ /* start pushing all the metadata that is currently dirty */
+ xfs_ail_push_all(mp->m_ail);
+ }
+ up_read(&mp->m_super->s_umount);
}

/* queue us up again */