xfs: shutdown xfs_sync_worker before the log

Revert commit 1307bbd, which uses the s_umount semaphore to provide
exclusion between xfs_sync_worker and unmount, in favor of shutting down
the sync worker before freeing the log in xfs_log_unmount.  This is a
cleaner way of resolving the race between xfs_sync_worker and unmount
than using s_umount.

Signed-off-by: Ben Myers <bpm@sgi.com>
Reviewed-by: Mark Tinguely <tinguely@sgi.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

2 files changed, 17 insertions, 16 deletions

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index f30d9807dc48..0e1a64f0439c 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -810,6 +810,7 @@ xfs_log_unmount_write(xfs_mount_t *mp)
 void
 xfs_log_unmount(xfs_mount_t *mp)
 {
+        cancel_delayed_work_sync(&mp->m_sync_work);
         xfs_trans_ail_destroy(mp);
         xlog_dealloc_log(mp->m_log);
 }
diff --git a/fs/xfs/xfs_sync.c b/fs/xfs/xfs_sync.c
index c9d3409c5ca3..1e9ee064dbb2 100644
--- a/fs/xfs/xfs_sync.c
+++ b/fs/xfs/xfs_sync.c
@@ -386,23 +386,23 @@ 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.  Use the s_umount semaphore to provide exclusion
-         * with unmount.
+         * during these times.  Use the MS_ACTIVE flag to avoid doing anything
+         * during mount.  Doing work during unmount is avoided by calling
+         * cancel_delayed_work_sync on this work queue before tearing down
+         * the ail and the log in xfs_log_unmount.
          */
-        if (down_read_trylock(&mp->m_super->s_umount)) {
-                if (!(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);
-
-                        /* start pushing all the metadata that is currently
-                         * dirty */
-                        xfs_ail_push_all(mp->m_ail);
-                }
-                up_read(&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);
+
+                /* start pushing all the metadata that is currently
+                 * dirty */
+                xfs_ail_push_all(mp->m_ail);
         }
 
         /* queue us up again */