Messages in this thread | | | Date | Thu, 21 Jun 2012 10:37:44 +0900 | From | Minchan Kim <> | Subject | Re: [PATCH] mm: offlining memory may block forever |
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On 06/21/2012 01:23 AM, Aaditya Kumar wrote:
> Offlining memory may block forever, waiting for kswapd() to wake up because > kswapd() does not check the event kthread->should_stop before sleeping.
>
> The proper pattern, from Documentation/memory-barriers.txt, is: > --- waker --- > event_indicated = 1; > wake_up_process(event_daemon); > > --- sleeper --- > for (;;) { > set_current_state(TASK_UNINTERRUPTIBLE); > if (event_indicated) > break; > schedule(); > } > > set_current_state() may be wrapped by: > prepare_to_wait(); > > In the kswapd() case, event_indicated is kthread->should_stop. > --- offlining memory (waker) --- > kswapd_stop() > kthread_stop() > kthread->should_stop = 1 > wake_up_process() > wait_for_completion() > > > --- kswapd_try_to_sleep (sleeper) --- > kswapd_try_to_sleep() > prepare_to_wait() > . > . > schedule() > . > . > finish_wait() > > The schedule() needs to be protected by a test of kthread->should_stop, > which is wrapped by kthread_should_stop(). > > Reproducer: > Do heavy file I/O in background. > Do a memory offline/online in a tight loop > > > Signed-off-by: Aaditya Kumar <aaditya.kumar@ap.sony.com>
Reviewed-by: Minchan Kim <minchan@kernel.org>
Nitpick: We can remove kthread_should_stop check earlier in kswapd_try_to_sleep. But it's no biggie. And I hope you change patch title
Title : Fix loss of kswapd wakeup in kswapd_stop Description: Offlining memory may block forever because blah, blah, blah.
-- Kind regards, Minchan Kim
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