linux-kernel - Re: INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected for kmemleak

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Date:	Wed, 02 Sep 2009 11:54:08 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Eric Paris <eparis@...hat.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected for
	kmemleak_lock

Hi Eric,

On Tue, 2009-09-01 at 16:55 -0400, Eric Paris wrote:
> I wrote a multithreaded inotify syscall pounder intended to create
> files, destroy files, create watches, and destroy watches with the
> maximum number of races possible.  Instead after letting it run a while
> I came upon this!  And then my system started to crash in all sorts of
> fun and glorious ways (kmem_cache_alloc bugs/panics/whatever)
> 
> -Eric
> 
> [ 2235.913737] ======================================================
> [ 2235.914084] [ INFO: HARDIRQ-safe -> HARDIRQ-unsafe lock order detected ]
> [ 2235.914084] 2.6.31-rc8-next-20090901 #64
> [ 2235.914084] ------------------------------------------------------
> [ 2235.914084] syscall_thrash/2516 [HC0[0]:SC0[0]:HE0:SE1] is trying to acquire:
> [ 2235.914084]  (kthread_create_lock){+.+...}, at: [<ffffffff81091543>] kthread_create+0x73/0x180
> [ 2235.914084] 
> [ 2235.914084] and this task is already holding:
> [ 2235.914084]  (kmemleak_lock){..----}, at: [<ffffffff81152611>] create_object+0x161/0x2e0
> [ 2235.914084] which would create a new lock dependency:
> [ 2235.914084]  (kmemleak_lock){..----} -> (kthread_create_lock){+.+...}

Are there other messages from kmemleak printed before that? It looks to
me like kmemleak got an exceptional situation (not being able to
allocate memory or inserting a pointer into the prio search tree) and it
disabled itself. When disabling, it starts a clean-up thread and AFAICT
that's the only condition when kmemleak_lock -> kthread_create_lock
dependency would be created.

I'm not sure whether disabling interrupts around kthread_run in
kmemleak_cleanup() would solve the problem. Otherwise, maybe the
kmemleak clean-up thread should take a different form or just a thread
waiting for a clean-up event (it currently acquires a mutex and cannot
be used in interrupt context).

Thanks.

-- 
Catalin

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