linux-kernel - [ 019/147] slab: fix the DEADLOCK issue on l3 alien lock

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Date:	Sun, 14 Oct 2012 15:35:52 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Michael Wang <wangyun@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Pekka Enberg <penberg@...nel.org>
Subject: [ 019/147] slab: fix the DEADLOCK issue on l3 alien lock

3.2-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Wang <wangyun@...ux.vnet.ibm.com>

commit 947ca1856a7e60aa6d20536785e6a42dff25aa6e upstream.

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.

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>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 mm/slab.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/mm/slab.c
+++ b/mm/slab.c
@@ -1669,9 +1669,6 @@ void __init kmem_cache_init_late(void)
 
 	g_cpucache_up = LATE;
 
-	/* Annotate slab for lockdep -- annotate the malloc caches */
-	init_lock_keys();
-
 	/* 6) resize the head arrays to their final sizes */
 	mutex_lock(&cache_chain_mutex);
 	list_for_each_entry(cachep, &cache_chain, next)
@@ -1679,6 +1676,9 @@ void __init kmem_cache_init_late(void)
 			BUG();
 	mutex_unlock(&cache_chain_mutex);
 
+	/* Annotate slab for lockdep -- annotate the malloc caches */
+	init_lock_keys();
+
 	/* Done! */
 	g_cpucache_up = FULL;
 


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