linux-kernel - Re: next-20090202: task kmemleak:763 blocked for more than 120 seconds.

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Date:	Mon, 2 Feb 2009 16:14:16 +0100
From:	Frédéric Weisbecker <fweisbec@...il.com>
To:	Catalin Marinas <catalin.marinas@....com>
Cc:	Alexander Beregalov <a.beregalov@...il.com>,
	"linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Mandeep Singh Baines <msb@...gle.com>
Subject: Re: next-20090202: task kmemleak:763 blocked for more than 120 
	seconds.

2009/2/2 Catalin Marinas <catalin.marinas@....com>:
> Alexander Beregalov <a.beregalov@...il.com> wrote:
>> It seems it is blocked forever.
>
> Scanning the full memory may take a lot of time, depending on the
> amount of RAM and the number of objects allocated. It is not unlikely
> to take more than 120 seconds on some loaded systems. However, it
> should call schedule() periodically to let other tasks run. Is your
> system unresponsive during this?
>
>> [ 1704.619898] INFO: task kmemleak:763 blocked for more than 120 seconds.
>> [ 1704.697951] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs"
>> disables this message.
>> [ 1704.791613] kmemleak      D 0000000000000001  6008   763      2
> [...]
>> [ 1706.246334] no locks held by kmemleak/763.
>
> It looks like the kmemleak thread is in the TASK_UNINTERUPTIBLE state.
> This happens when it calls schedule_timeout_uninterruptible() to sleep
> between scans. It probably took more than 120 to scan the memory and
> hence the report.
>
> It doesn't look like a problem, only that the watchdog thread checks
> for uninterruptible tasks. I can try to make it sleep with
> TASK_INTERRUPTIBLE to avoid the message.
>
> Thanks.
>
> --
> Catalin
> --


Hi,

May be it would be better to make the softlockup detector hooking into
schedule_timeout()
(ie by using a tracepoint) to check if a thread chose to sleep more
than hung_task_timeout_secs
intentionally in a TASK_UNINTERRUPTIBLE state.

Fixing it into kmemleak would not solve the problem in other tasks
which do similar sleeps...

Mandeep, if you want I can try something? Or perhaps you prefer to do
it yourself. As you wish.
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