[patch-stable 2.6.16] pdflush: handle resume wakeups

[Pavel Machek <pavel@ucw.cz>]

2.6.16 needs this. It was merged into 2.6.18-rc1 in
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=d616e09ab33aa4d013a93c9b393efd5cebf78521 .

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: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Signed-off-by: Pavel Machek <pavel@suse.cz>

diff -urN linux-suse/mm/pdflush.c linux/mm/pdflush.c
--- linux-suse/mm/pdflush.c	2006-07-06 11:51:11.000000000 -0400
+++ linux/mm/pdflush.c	2006-07-06 11:51:57.000000000 -0400
@@ -104,21 +104,20 @@
 		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);


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