[PATCH] pdflush: handle resume wakeups

pdflush is carefully designed to ensure that all wakeups have some
corresponding work to do - if a woken-up pdflush thread discovers that it
hasn't been given any work to do then this is considered an error.

That all broke when swsusp came along - because a timer-delivered wakeup to a
frozen pdflush thread will just get lost.  This causes the pdflush thread to
get lost as well: the writeback timer is supposed to be re-armed by pdflush in
process context, but pdflush doesn't execute the callout which does this.

Fix that up by ignoring the return value from try_to_freeze(): jsut proceed,
see if we have any work pending and only go back to sleep if that is not the
case.
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>

mm/pdflush.c

@@ -104,21 +104,20 @@ static int __pdflush(struct pdflush_work *my_work)
 		list_move(&my_work->list, &pdflush_list);
 		my_work->when_i_went_to_sleep = jiffies;
 		spin_unlock_irq(&pdflush_lock);
-
 		schedule();
-		if (try_to_freeze()) {
-			spin_lock_irq(&pdflush_lock);
-			continue;
-		}
-
+		try_to_freeze();
 		spin_lock_irq(&pdflush_lock);
 		if (!list_empty(&my_work->list)) {
-			printk("pdflush: bogus wakeup!\n");
+			/*
+			 * Someone woke us up, but without removing our control
+			 * structure from the global list.  swsusp will do this
+			 * in try_to_freeze()->refrigerator().  Handle it.
+			 */
 			my_work->fn = NULL;
 			continue;
 		}
 		if (my_work->fn == NULL) {
-			printk("pdflush: NULL work function\n");
+			printk("pdflush: bogus wakeup\n");
 			continue;
 		}
 		spin_unlock_irq(&pdflush_lock);