linux-kernel - Re: [2.6.32-rc3 kmemleak] WARNING: at kernel/lockdep.c:3161check

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Message-Id: <1255435201.9987.22.camel@pc1117.cambridge.arm.com>
Date:	Tue, 13 Oct 2009 13:00:01 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>
Cc:	paulmck@...ux.vnet.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [2.6.32-rc3 kmemleak] WARNING: at
	kernel/lockdep.c:3161check_flags+0xbe/0x180()

On Tue, 2009-10-13 at 12:17 +0900, Tetsuo Handa wrote:
> Catalin Marinas wrote:
> > On Thu, 2009-10-08 at 21:34 +0900, Tetsuo Handa wrote:
> > > If the stack dump is correct, this error indicates circular function calls.
> > > We need to find the location which triggers circular memory allocation.
> > > Maybe just checking for NULL is not sufficient.
> > 
> > The circular function call is expected, nothing to do with the NULL
> > checking. You get callbacks from the slab allocator into kmemleak which
> > also allocates memory (but this latter call isn't traced - similar
> > behaviour in kmemtrace).
> 
> So, something is preventing kmemleak from being traced, isn't it?

The SLAB_NOLEAKTRACE flag is preventing kmemleak from tracing itself
since it needs to do some memory allocations for its internal data.

When kmemleak calls the slab allocator, it uses the GFP_KERNEL|
GFP_ATOMIC flags passed by the original alloc caller to the slab
allocator. Is there any other flag that would need to be preserved? If
the alloc caller doesn't use GFP_ATOMIC when it should, neither does
kmemleak so you would also get a warning in kmemleak.

But in this particular case, you say that disabling kmemleak no longer
shows this warning.

> I tried 2.6.32-rc4 , but the error is not yet fixed. How can I help you?
> 
> [    0.000000] Linux version 2.6.32-rc4 (root@...oyo) (gcc version 3.3.5 (Debian 1:3.3.5-13)) #2 SMP Tue Oct 13 11:10:53 JST 2009
> (...snipped...)
> [    0.000000] -------------------------------------------------------
> [    0.000000] Good, all 218 testcases passed! |
> [    0.000000] ---------------------------------
> [    0.000000] ------------[ cut here ]------------
> [    0.000000] WARNING: at kernel/lockdep.c:3161 check_flags+0xbe/0x180()
> [    0.000000] Hardware name: VMware Virtual Platform
> [    0.000000] Modules linked in:
> [    0.000000] Pid: 0, comm: swapper Not tainted 2.6.32-rc4 #2
> [    0.000000] Call Trace:
> [    0.000000]  [<c10417dd>] ? printk+0x1d/0x30
> [    0.000000]  [<c10703ae>] ? check_flags+0xbe/0x180
> [    0.000000]  [<c1040d91>] warn_slowpath_common+0x81/0xa0
> [    0.000000]  [<c10703ae>] ? check_flags+0xbe/0x180
> [    0.000000]  [<c1040e0a>] warn_slowpath_null+0x1a/0x30
> [    0.000000]  [<c10703ae>] check_flags+0xbe/0x180
> [    0.000000]  [<c106e23e>] lockdep_trace_alloc+0x2e/0x60
> [    0.000000]  [<c10cfded>] kmem_cache_alloc+0x2d/0x1d0
> [    0.000000]  [<c106e00b>] ? trace_hardirqs_off+0xb/0x10
> [    0.000000]  [<c10ceeaf>] ? alloc_slabmgmt+0x5f/0x80
> [    0.000000]  [<c10ceeaf>] alloc_slabmgmt+0x5f/0x80
> [    0.000000]  [<c10cf2ee>] cache_grow+0xae/0x170
> [    0.000000]  [<c10cf90b>] cache_alloc_refill+0x17b/0x210
> [    0.000000]  [<c10cff6a>] kmem_cache_alloc+0x1aa/0x1d0
> [    0.000000]  [<c10cd8c8>] ? obj_size+0x8/0x10
> [    0.000000]  [<c10d3879>] ? create_object+0x29/0x220
> [    0.000000]  [<c10d3879>] create_object+0x29/0x220
> [    0.000000]  [<c10cd8b8>] ? obj_offset+0x8/0x10
> [    0.000000]  [<c10cdf8a>] ? poison_obj+0x2a/0x50
> [    0.000000]  [<c1321613>] kmemleak_alloc+0x83/0xd0
> [    0.000000]  [<c10ceeaf>] ? alloc_slabmgmt+0x5f/0x80
> [    0.000000]  [<c10cff45>] kmem_cache_alloc+0x185/0x1d0
> [    0.000000]  [<c10ceeaf>] ? alloc_slabmgmt+0x5f/0x80
> [    0.000000]  [<c10ceeaf>] alloc_slabmgmt+0x5f/0x80
> [    0.000000]  [<c10cf2ee>] cache_grow+0xae/0x170
> [    0.000000]  [<c10cf90b>] cache_alloc_refill+0x17b/0x210
> [    0.000000]  [<c10cff6a>] kmem_cache_alloc+0x1aa/0x1d0
> [    0.000000]  [<c10cd8c8>] ? obj_size+0x8/0x10
> [    0.000000]  [<c10d3879>] ? create_object+0x29/0x220
> [    0.000000]  [<c10d3879>] create_object+0x29/0x220

This is the "DEBUG_LOCKS_WARN_ON(current->softirqs_enabled)" warning.
I'm not sure why this happens but from the trace it seems that kmemleak
is being called recursively via alloc_slabmgmt() which is caused by
kmem_cache_alloc() called from create_object() in kmemleak.c.

Could you send me your .config file and I'll try to reproduce this as
well?

Thanks.

-- 
Catalin

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