xfs: give all workqueues rescuer threads

We're consistently hitting deadlocks here with XFS on recent kernels.
After some digging through the crash files, it looks like everyone in
the system is waiting for XFS to reclaim memory.

Something like this:

PID: 2733434  TASK: ffff8808cd242800  CPU: 19  COMMAND: "java"
 #0 [ffff880019c53588] __schedule at ffffffff818c4df2
 #1 [ffff880019c535d8] schedule at ffffffff818c5517
 #2 [ffff880019c535f8] _xfs_log_force_lsn at ffffffff81316348
 #3 [ffff880019c53688] xfs_log_force_lsn at ffffffff813164fb
 #4 [ffff880019c536b8] xfs_iunpin_wait at ffffffff8130835e
 #5 [ffff880019c53728] xfs_reclaim_inode at ffffffff812fd453
 torvalds#6 [ffff880019c53778] xfs_reclaim_inodes_ag at ffffffff812fd8c7
 torvalds#7 [ffff880019c53928] xfs_reclaim_inodes_nr at ffffffff812fe433
 torvalds#8 [ffff880019c53958] xfs_fs_free_cached_objects at ffffffff8130d3b9
 torvalds#9 [ffff880019c53968] super_cache_scan at ffffffff811a6f73
torvalds#10 [ffff880019c539c8] shrink_slab at ffffffff811460e6
torvalds#11 [ffff880019c53aa8] shrink_zone at ffffffff8114a53f
torvalds#12 [ffff880019c53b48] do_try_to_free_pages at ffffffff8114a8ba
torvalds#13 [ffff880019c53be8] try_to_free_pages at ffffffff8114ad5a
torvalds#14 [ffff880019c53c78] __alloc_pages_nodemask at ffffffff8113e1b8
torvalds#15 [ffff880019c53d88] alloc_kmem_pages_node at ffffffff8113e671
torvalds#16 [ffff880019c53dd8] copy_process at ffffffff8104f781
torvalds#17 [ffff880019c53ec8] do_fork at ffffffff8105129c
torvalds#18 [ffff880019c53f38] sys_clone at ffffffff810515b6
torvalds#19 [ffff880019c53f48] stub_clone at ffffffff818c8e4d

xfs_log_force_lsn is waiting for logs to get cleaned, which is waiting
for IO, which is waiting for workers to complete the IO which is waiting
for worker threads that don't exist yet:

PID: 2752451  TASK: ffff880bd6bdda00  CPU: 37  COMMAND: "kworker/37:1"
 #0 [ffff8808d20abbb0] __schedule at ffffffff818c4df2
 #1 [ffff8808d20abc00] schedule at ffffffff818c5517
 #2 [ffff8808d20abc20] schedule_timeout at ffffffff818c7c6c
 #3 [ffff8808d20abcc0] wait_for_completion_killable at ffffffff818c6495
 #4 [ffff8808d20abd30] kthread_create_on_node at ffffffff8106ec82
 #5 [ffff8808d20abdf0] create_worker at ffffffff8106752f
 torvalds#6 [ffff8808d20abe40] worker_thread at ffffffff810699be
 torvalds#7 [ffff8808d20abec0] kthread at ffffffff8106ef59
 torvalds#8 [ffff8808d20abf50] ret_from_fork at ffffffff818c8ac8

I think we should be using WQ_MEM_RECLAIM to make sure this thread
pool makes progress when we're not able to allocate new workers.

[dchinner: make all workqueues WQ_MEM_RECLAIM]

Signed-off-by: Chris Mason <clm@fb.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_super.c

@@ -838,17 +838,18 @@ xfs_init_mount_workqueues(
 		goto out_destroy_unwritten;
 
 	mp->m_reclaim_workqueue = alloc_workqueue("xfs-reclaim/%s",
-			WQ_FREEZABLE, 0, mp->m_fsname);
+			WQ_MEM_RECLAIM|WQ_FREEZABLE, 0, mp->m_fsname);
 	if (!mp->m_reclaim_workqueue)
 		goto out_destroy_cil;
 
 	mp->m_log_workqueue = alloc_workqueue("xfs-log/%s",
-			WQ_FREEZABLE|WQ_HIGHPRI, 0, mp->m_fsname);
+			WQ_MEM_RECLAIM|WQ_FREEZABLE|WQ_HIGHPRI, 0,
+			mp->m_fsname);
 	if (!mp->m_log_workqueue)
 		goto out_destroy_reclaim;
 
 	mp->m_eofblocks_workqueue = alloc_workqueue("xfs-eofblocks/%s",
-			WQ_FREEZABLE, 0, mp->m_fsname);
+			WQ_MEM_RECLAIM|WQ_FREEZABLE, 0, mp->m_fsname);
 	if (!mp->m_eofblocks_workqueue)
 		goto out_destroy_log;