linux-kernel - Re: kmemleak not tainted

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Date:	Tue, 07 Jul 2009 14:22:21 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...l.by>
Cc:	Pekka Enberg <penberg@...helsinki.fi>, Ingo Molnar <mingo@...e.hu>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: kmemleak not tainted

On Tue, 2009-07-07 at 16:17 +0300, Sergey Senozhatsky wrote:
> > On Tue, 2009-07-07 at 14:51 +0300, Sergey Senozhatsky wrote:
> > > kernel: [ 1917.133154] INFO: RCU detected CPU 0 stall (t=485140/3000 jiffies)
[...]
> > What I think happens is that the kmemleak thread runs for several
> > seconds for scanning the memory and there may not be any context
> > switches. I have a patch to add more cond_resched() calls throughout the
> > kmemleak_scan() function which I hope will get merged. 
[...]
> > I don't get any  of these messages with CONFIG_PREEMPT enabled.
> 
> It started with rc2-git1 (may be). Almost every scan ends with RCU pending.

Should I assume that CONFIG_PREEMPT is disabled on your system?

The branch with the pending kmemleak patches is below (I sent Linus a
pull request):

http://www.linux-arm.org/git?p=linux-2.6.git;a=shortlog;h=kmemleak

You can try the "Add more cond_resched() calls..." patch and see if it
makes any difference.

> Hm.. Something is broken...
> cat /.../kmemleak
> [ 7933.537868] ================================================
> [ 7933.537873] [ BUG: lock held when returning to user space! ]
> [ 7933.537876] ------------------------------------------------
> [ 7933.537880] cat/2897 is leaving the kernel with locks still held!
> [ 7933.537884] 1 lock held by cat/2897:
> [ 7933.537887]  #0:  (scan_mutex){+.+.+.}, at: [<c10f717c>] kmemleak_open+0x4c/0x80

That the "Do not acquire scan_mutex in kmemleak_open()" patch in the
same branch.

-- 
Catalin

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