linux-kernel - Re: Patch Upstream: slab: fix the DEADLOCK issue on l3 alien lock

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Message-ID: <20121008154952.GA27015@kroah.com>
Date:	Mon, 8 Oct 2012 08:49:52 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Peter Zijlstra <peterz@...radead.org>,
	Christoph Lameter <cl@...ux.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	Pekka Enberg <penberg@...nel.org>
Cc:	stable@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Patch Upstream: slab: fix the DEADLOCK issue on l3 alien lock

On Sun, Oct 07, 2012 at 10:39:44AM -0400, Gregs git-bot wrote:
> commit: 947ca1856a7e60aa6d20536785e6a42dff25aa6e
> From: Michael Wang <wangyun@...ux.vnet.ibm.com>
> Date: Wed, 5 Sep 2012 10:33:18 +0800
> Subject: slab: fix the DEADLOCK issue on l3 alien lock
> 
> DEADLOCK will be report while running a kernel with NUMA and LOCKDEP enabled,
> the process of this fake report is:
> 
> 	   kmem_cache_free()	//free obj in cachep
> 	-> cache_free_alien()	//acquire cachep's l3 alien lock
> 	-> __drain_alien_cache()
> 	-> free_block()
> 	-> slab_destroy()
> 	-> kmem_cache_free()	//free slab in cachep->slabp_cache
> 	-> cache_free_alien()	//acquire cachep->slabp_cache's l3 alien lock
> 
> Since the cachep and cachep->slabp_cache's l3 alien are in the same lock class,
> fake report generated.
> 
> This should not happen since we already have init_lock_keys() which will
> reassign the lock class for both l3 list and l3 alien.
> 
> However, init_lock_keys() was invoked at a wrong position which is before we
> invoke enable_cpucache() on each cache.
> 
> Since until set slab_state to be FULL, we won't invoke enable_cpucache()
> on caches to build their l3 alien while creating them, so although we invoked
> init_lock_keys(), the l3 alien lock class won't change since we don't have
> them until invoked enable_cpucache() later.
> 
> This patch will invoke init_lock_keys() after we done enable_cpucache()
> instead of before to avoid the fake DEADLOCK report.
> 
> Michael traced the problem back to a commit in release 3.0.0:
> 
> commit 30765b92ada267c5395fc788623cb15233276f5c
> Author: Peter Zijlstra <peterz@...radead.org>
> Date:   Thu Jul 28 23:22:56 2011 +0200
> 
>     slab, lockdep: Annotate the locks before using them
> 
>     Fernando found we hit the regular OFF_SLAB 'recursion' before we
>     annotate the locks, cure this.
> 
>     The relevant portion of the stack-trace:
> 
>     > [    0.000000]  [<c085e24f>] rt_spin_lock+0x50/0x56
>     > [    0.000000]  [<c04fb406>] __cache_free+0x43/0xc3
>     > [    0.000000]  [<c04fb23f>] kmem_cache_free+0x6c/0xdc
>     > [    0.000000]  [<c04fb2fe>] slab_destroy+0x4f/0x53
>     > [    0.000000]  [<c04fb396>] free_block+0x94/0xc1
>     > [    0.000000]  [<c04fc551>] do_tune_cpucache+0x10b/0x2bb
>     > [    0.000000]  [<c04fc8dc>] enable_cpucache+0x7b/0xa7
>     > [    0.000000]  [<c0bd9d3c>] kmem_cache_init_late+0x1f/0x61
>     > [    0.000000]  [<c0bba687>] start_kernel+0x24c/0x363
>     > [    0.000000]  [<c0bba0ba>] i386_start_kernel+0xa9/0xaf
> 
>     Reported-by: Fernando Lopez-Lezcano <nando@...ma.Stanford.EDU>
>     Acked-by: Pekka Enberg <penberg@...nel.org>
>     Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
>     Link: http://lkml.kernel.org/r/1311888176.2617.379.camel@laptop
>     Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> The commit moved init_lock_keys() before we build up the alien, so we
> failed to reclass it.
> 
> Cc: <stable@...r.kernel.org> # 3.0+
> Acked-by: Christoph Lameter <cl@...ux.com>
> Tested-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> Signed-off-by: Michael Wang <wangyun@...ux.vnet.ibm.com>
> Signed-off-by: Pekka Enberg <penberg@...nel.org>


The commit above shows up in 3.1, not 3.0, so this patch does not apply
to the 3.0.y kernel from what I can tell.  If this is incorrect, please
let me know.

thanks,

greg k-h
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