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SubjectRe: [PATCH] Page writeback broken after resume: wb_timer lost
Pavel Machek <pavel@ucw.cz> wrote:
>
> Refrigerator looks like this:
>
> /* Refrigerator is place where frozen processes are stored :-). */
> void refrigerator(void)
> {
> /* Hmm, should we be allowed to suspend when there are
> realtime
> processes around? */
> long save;
> save = current->state;
> pr_debug("%s entered refrigerator\n", current->comm);
> printk("=");
>
> frozen_process(current);
> spin_lock_irq(&current->sighand->siglock);
> recalc_sigpending(); /* We sent fake signal, clean it up */
> spin_unlock_irq(&current->sighand->siglock);
>
> while (frozen(current)) {
> current->state = TASK_UNINTERRUPTIBLE;
> schedule();
> }
> pr_debug("%s left refrigerator\n", current->comm);
> current->state = save;
> }

Well that's a crock, isn't it?


Peter, does this fix it?


From: Andrew Morton <akpm@osdl.org>

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>
---

mm/pdflush.c | 9 ++-------
1 files changed, 2 insertions(+), 7 deletions(-)

diff -puN mm/pdflush.c~pdflush-handle-resume-wakeups mm/pdflush.c
--- devel/mm/pdflush.c~pdflush-handle-resume-wakeups 2006-05-20 17:02:21.000000000 -0700
+++ devel-akpm/mm/pdflush.c 2006-05-20 17:11:25.000000000 -0700
@@ -104,13 +104,8 @@ static int __pdflush(struct pdflush_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");
@@ -118,7 +113,7 @@ static int __pdflush(struct pdflush_work
continue;
}
if (my_work->fn == NULL) {
- printk("pdflush: NULL work function\n");
+ printk("pflush: resuming\n");
continue;
}
spin_unlock_irq(&pdflush_lock);
_


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