xfs: stop the sync worker before xfs_unmountfs

[Ben Myers <bpm@xxxxxxx>]

See what you think of this.  Not heavily tested yet, and not pretty... but it
is fairly minimal. 

Pull startup and shutdown of the sync worker out of xfs_syncd_init and
xfs_syncd_stop into their callers.  In the case of unmount, move shutdown of
the xfs_sync_worker before teardown of the log in xfs_unmountfs.  This prevents
occasional crashes on unmount like so:

PID: 21602  TASK: ee9df060  CPU: 0   COMMAND: "kworker/0:3"                     
                                                                                
                          
 #0 [c5377d28] crash_kexec at c0292c94                                          
                                                                                
                          
 #1 [c5377d80] oops_end at c07090c2                                             
                                                                                
                          
 #2 [c5377d98] no_context at c06f614e                                           
                                                                                
                          
 #3 [c5377dbc] __bad_area_nosemaphore at c06f6281                               
                                                                                
                          
 #4 [c5377df4] bad_area_nosemaphore at c06f629b                                 
                                                                                
                          
 #5 [c5377e00] do_page_fault at c070b0cb                                        
                                                                                
                          
 #6 [c5377e7c] error_code (via page_fault) at c070892c                          
                                                                                
                          
    EAX: f300c6a8  EBX: f300c6a8  ECX: 000000c0  EDX: 000000c0  EBP: c5377ed0   
                                                                                
                          
    DS:  007b      ESI: 00000000  ES:  007b      EDI: 00000001  GS:  ffffad20   
                                                                                
                          
    CS:  0060      EIP: c0481ad0  ERR: ffffffff  EFLAGS: 00010246               
                                                                                
                          
 #7 [c5377eb0] atomic64_read_cx8 at c0481ad0                                    
                                                                                
                          
 #8 [c5377ebc] xlog_assign_tail_lsn_locked at f7cc7c6e [xfs]                    
                                                                                
                          
 #9 [c5377ed4] xfs_trans_ail_delete_bulk at f7ccd520 [xfs]                      
                                                                                
                          
#10 [c5377f0c] xfs_buf_iodone at f7ccb602 [xfs]                                 
                                                                                
                          
#11 [c5377f24] xfs_buf_do_callbacks at f7cca524 [xfs]                           
                                                                                
                          
#12 [c5377f30] xfs_buf_iodone_callbacks at f7cca5da [xfs]                       
                                                                                
                          
#13 [c5377f4c] xfs_buf_iodone_work at f7c718d0 [xfs]                            
                                                                                
                          
#14 [c5377f58] process_one_work at c024ee4c                                     
                                                                                
                          
#15 [c5377f98] worker_thread at c024f43d                                        
                                                                                
                          
#16 [c5377fbc] kthread at c025326b                                              
                                                                                
                          
#17 [c5377fe8] kernel_thread_helper at c070e834                                 
                                                                                
                          
                                                                                
                                                                                
                          
PID: 26653  TASK: e79143b0  CPU: 3   COMMAND: "umount"                          
                                                                                
                          
 #0 [cde0fda0] __schedule at c0706595                                           
                                                                                
                          
 #1 [cde0fe28] schedule at c0706b89                                             
                                                                                
                          
 #2 [cde0fe30] schedule_timeout at c0705600                                     
                                                                                
                          
 #3 [cde0fe94] __down_common at c0706098                                        
                                                                                
                          
 #4 [cde0fec8] __down at c0706122                                               
                                                                                
                          
 #5 [cde0fed0] down at c025936f                                                 
                                                                                
                          
 #6 [cde0fee0] xfs_buf_lock at f7c7131d [xfs]                                   
                                                                                
                          
 #7 [cde0ff00] xfs_freesb at f7cc2236 [xfs]                                     
                                                                                
                          
 #8 [cde0ff10] xfs_fs_put_super at f7c80f21 [xfs]                               
                                                                                
                          
 #9 [cde0ff1c] generic_shutdown_super at c0333d7a                               
                                                                                
                          
#10 [cde0ff38] kill_block_super at c0333e0f                                     
                                                                                
                          
#11 [cde0ff48] deactivate_locked_super at c0334218                              
                                                                                
                          
#12 [cde0ff58] deactivate_super at c033495d                                     
                                                                                
                          
#13 [cde0ff68] mntput_no_expire at c034bc13                                     
                                                                                
                          
#14 [cde0ff7c] sys_umount at c034cc69                                           
                                                                                
                          
#15 [cde0ffa0] sys_oldumount at c034ccd4                                        
                                                                                
                          
#16 [cde0ffb0] system_call at c0707e66 

Signed-off-by: Ben Myers <bpm@xxxxxxx>

Index: xfs/fs/xfs/xfs_super.c
===================================================================
--- xfs.orig/fs/xfs/xfs_super.c
+++ xfs/fs/xfs/xfs_super.c
@@ -919,6 +919,7 @@ xfs_fs_put_super(
        struct xfs_mount        *mp = XFS_M(sb);
 
        xfs_filestream_unmount(mp);
+       cancel_delayed_work_sync(&mp->m_sync_work);
        xfs_unmountfs(mp);
        xfs_syncd_stop(mp);
        xfs_freesb(mp);
@@ -1210,6 +1211,9 @@ xfs_finish_flags(
        return 0;
 }
 
+extern void xfs_sync_worker(struct work_struct *);
+extern void xfs_syncd_queue_sync(struct xfs_mount *);
+
 STATIC int
 xfs_fs_fill_super(
        struct super_block      *sb,
@@ -1291,6 +1295,8 @@ xfs_fs_fill_super(
        set_posix_acl_flag(sb);
 
        error = xfs_syncd_init(mp);
+       INIT_DELAYED_WORK(&mp->m_sync_work, xfs_sync_worker);
+       xfs_syncd_queue_sync(mp);
        if (error)
                goto out_filestream_unmount;
 
@@ -1315,6 +1321,7 @@ xfs_fs_fill_super(
 
        return 0;
  out_syncd_stop:
+       cancel_delayed_work_sync(&mp->m_sync_work);
        xfs_syncd_stop(mp);
  out_filestream_unmount:
        xfs_filestream_unmount(mp);
@@ -1335,6 +1342,7 @@ out_destroy_workqueues:
  out_unmount:
        xfs_filestream_unmount(mp);
        xfs_unmountfs(mp);
+       cancel_delayed_work_sync(&mp->m_sync_work);
        xfs_syncd_stop(mp);
        goto out_free_sb;
 }
Index: xfs/fs/xfs/xfs_sync.c
===================================================================
--- xfs.orig/fs/xfs/xfs_sync.c
+++ xfs/fs/xfs/xfs_sync.c
@@ -370,7 +370,7 @@ xfs_quiesce_attr(
        xfs_buf_unlock(mp->m_sb_bp);
 }
 
-static void
+void
 xfs_syncd_queue_sync(
        struct xfs_mount        *mp)
 {
@@ -383,7 +383,7 @@ xfs_syncd_queue_sync(
  * disk quotas.  We might need to cover the log to indicate that the
  * filesystem is idle and not frozen.
  */
-STATIC void
+void
 xfs_sync_worker(
        struct work_struct *work)
 {
@@ -494,11 +494,8 @@ xfs_syncd_init(
        struct xfs_mount        *mp)
 {
        INIT_WORK(&mp->m_flush_work, xfs_flush_worker);
-       INIT_DELAYED_WORK(&mp->m_sync_work, xfs_sync_worker);
        INIT_DELAYED_WORK(&mp->m_reclaim_work, xfs_reclaim_worker);
 
-       xfs_syncd_queue_sync(mp);
-
        return 0;
 }
 
@@ -506,7 +503,6 @@ void
 xfs_syncd_stop(
        struct xfs_mount        *mp)
 {
-       cancel_delayed_work_sync(&mp->m_sync_work);
        cancel_delayed_work_sync(&mp->m_reclaim_work);
        cancel_work_sync(&mp->m_flush_work);
 }