xfs: Make xfsaild freezeable again

Hendik has reported suspend failures due to xfsaild blocking the freezer
to settle down.
Jan 17 19:59:56 linux-6380 kernel: PM: Syncing filesystems ... done.
Jan 17 19:59:56 linux-6380 kernel: PM: Preparing system for sleep (mem)
Jan 17 19:59:56 linux-6380 kernel: Freezing user space processes ... (elapsed 0.001 seconds) done.
Jan 17 19:59:56 linux-6380 kernel: Freezing remaining freezable tasks ...
Jan 17 19:59:56 linux-6380 kernel: Freezing of tasks failed after 20.002 seconds (1 tasks refusing to freeze, wq_busy=0):
Jan 17 19:59:56 linux-6380 kernel: xfsaild/dm-5    S 00000000     0  1293      2 0x00000080
Jan 17 19:59:56 linux-6380 kernel:  f0ef5f00 00000046 00000200 00000000 ffff9022 c02d3800 00000000 00000032
Jan 17 19:59:56 linux-6380 kernel:  ee0b2400 00000032 f71e0d00 f36fabc0 f0ef2d00 f0ef6000 f0ef2d00 f12f90c0
Jan 17 19:59:56 linux-6380 kernel:  f0ef5f0c c0844e44 00000000 f0ef5f6c f811e0be 00000000 00000000 f0ef2d00
Jan 17 19:59:56 linux-6380 kernel: Call Trace:
Jan 17 19:59:56 linux-6380 kernel:  [<c0844e44>] schedule+0x34/0x90
Jan 17 19:59:56 linux-6380 kernel:  [<f811e0be>] xfsaild+0x5de/0x600 [xfs]
Jan 17 19:59:56 linux-6380 kernel:  [<c0286cbb>] kthread+0x9b/0xb0
Jan 17 19:59:56 linux-6380 kernel:  [<c0848a79>] ret_from_kernel_thread+0x21/0x38

The issue has been there for quite some time but it has been made
visible by only by 24ba16bb ("xfs: clear PF_NOFREEZE for xfsaild
kthread") because the suspend started seeing xfsaild.

The above commit has missed that the !xfs_ail_min branch might call
schedule with TASK_INTERRUPTIBLE without calling try_to_freeze so the pm
suspend would wake up the kernel thread over and over again without any
progress. What we want here is to use freezable_schedule instead to hide
the thread from the suspend.

While we are here also change schedule_timeout to freezable variant to
prevent from spurious wakeups by suspend.

[dchinner: re-add set_freezeable call so the freezer will account properly
 for this kthread. ]
Reported-by: NHendrik Woltersdorf <hendrikw@arcor.de>
Signed-off-by: NMichal Hocko <mhocko@suse.com>
Reviewed-by: NDave Chinner <dchinner@redhat.com>
Signed-off-by: NDave Chinner <david@fromorbit.com>

fs/xfs/xfs_trans_ail.c

@@ -497,6 +497,7 @@ xfsaild(
 	long		tout = 0;	/* milliseconds */
 
 	current->flags |= PF_MEMALLOC;
+	set_freezable();
 
 	while (!kthread_should_stop()) {
 		if (tout && tout <= 20)
@@ -519,14 +520,14 @@ xfsaild(
 		if (!xfs_ail_min(ailp) &&
 		    ailp->xa_target == ailp->xa_target_prev) {
 			spin_unlock(&ailp->xa_lock);
-			schedule();
+			freezable_schedule();
 			tout = 0;
 			continue;
 		}
 		spin_unlock(&ailp->xa_lock);
 
 		if (tout)
-			schedule_timeout(msecs_to_jiffies(tout));
+			freezable_schedule_timeout(msecs_to_jiffies(tout));
 
 		__set_current_state(TASK_RUNNING);