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Message-ID: <CAOJsxLFR0uqxJRysz+r5ojqPe0A4q14LeOuinSBPrNKbYuAAxw@mail.gmail.com>
Date: Wed, 9 May 2012 09:34:24 +0300
From: Pekka Enberg <penberg@...nel.org>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Andrey Vagin <avagin@...nvz.org>,
LKML <linux-kernel@...r.kernel.org>,
Christoph Lameter <cl@...ux-foundation.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: lockdep reports about recursive locking in kmemleak
On Mon, Apr 30, 2012 at 2:04 PM, Catalin Marinas
<catalin.marinas@....com> wrote:
> On Fri, Apr 27, 2012 at 12:30:36PM +0100, Andrey Vagin wrote:
>> I found a following message in dmesg. Probably we should to do something
>> similar as for debug_objects, it sets own class for parent->list_lock.
>> Does anyone want to fix that?
>>
>> =============================================
>> [ INFO: possible recursive locking detected ]
>> 3.3.0+ #87 Not tainted
>> ---------------------------------------------
>> udevd/847 is trying to acquire lock:
>> (&(&parent->list_lock)->rlock){-.-...}, at: [<ffffffff811783f1>]
>> cache_alloc_refill+0xa1/0x300
>>
>> but task is already holding lock:
>> (&(&parent->list_lock)->rlock){-.-...}, at: [<ffffffff81177628>]
>> cache_flusharray+0x68/0x180
>>
>> other info that might help us debug this:
>> Possible unsafe locking scenario:
>>
>> CPU0
>> ----
>> lock(&(&parent->list_lock)->rlock);
>> lock(&(&parent->list_lock)->rlock);
>>
>> *** DEADLOCK ***
>>
>> May be due to missing lock nesting notation
>>
>> 1 lock held by udevd/847:
>> #0: (&(&parent->list_lock)->rlock){-.-...}, at: [<ffffffff81177628>]
>> cache_flusharray+0x68/0x180
>
> I'm not sure what the right fix is (cc'ing Christoph for the slab.c
> code). The lockdep warning is not in kmemleak, it just happens that
> cache_flusharray() (holding an l3->list_lock) triggers a new allocation
> via debug_object_activate() and kmemleak also tries to allocate its
> metadata, causing a cache_alloc_refill() call which acquires a
> different l3->list_lock, hence the lockdep warning.
How do we know it's always a different nodelist ("l3")?
> Below is a quick fix but I don't know whether it could hide a real
> problem in the future:
>
> diff --git a/mm/slab.c b/mm/slab.c
> index e901a36..3d2bfc6 100644
> --- a/mm/slab.c
> +++ b/mm/slab.c
> @@ -3143,7 +3143,7 @@ retry:
> l3 = cachep->nodelists[node];
>
> BUG_ON(ac->avail > 0 || !l3);
> - spin_lock(&l3->list_lock);
> + spin_lock_nested(&l3->list_lock, SINGLE_DEPTH_NESTING);
>
> /* See if we can refill from the shared array */
> if (l3->shared && transfer_objects(ac, l3->shared, batchcount)) {
>
>
> I'm leaving the original stack trace below for reference.
Lockdep and slab... I'm CC'ing Peter (sorry!) :-)
>> stack backtrace:
>> Pid: 847, comm: udevd Not tainted 3.3.0+ #87
>> Call Trace:
>> [<ffffffff810b835a>] __lock_acquire+0x126a/0x1730
>> [<ffffffff810b73f2>] ? __lock_acquire+0x302/0x1730
>> [<ffffffff810b88d1>] lock_acquire+0xb1/0x1a0
>> [<ffffffff811783f1>] ? cache_alloc_refill+0xa1/0x300
>> [<ffffffff8118cdb9>] ? create_object+0x39/0x2e0
>> [<ffffffff8153a141>] _raw_spin_lock+0x41/0x50
>> [<ffffffff811783f1>] ? cache_alloc_refill+0xa1/0x300
>> [<ffffffff811783f1>] cache_alloc_refill+0xa1/0x300
>> [<ffffffff810b73f2>] ? __lock_acquire+0x302/0x1730
>> [<ffffffff8118cdb9>] ? create_object+0x39/0x2e0
>> [<ffffffff81179cbc>] kmem_cache_alloc+0x2cc/0x320
>> [<ffffffff8118cdb9>] create_object+0x39/0x2e0
>> [<ffffffff810b73f2>] ? __lock_acquire+0x302/0x1730
>> [<ffffffff8151fade>] kmemleak_alloc+0x5e/0xc0
>> [<ffffffff81179b2c>] kmem_cache_alloc+0x13c/0x320
>> [<ffffffff81294d99>] __debug_object_init+0x3b9/0x3d0
>> [<ffffffff812944fa>] ? debug_object_activate+0xca/0x190
>> [<ffffffff81294dff>] debug_object_init+0x1f/0x30
>> [<ffffffff810767d7>] rcuhead_fixup_activate+0x27/0x70
>> [<ffffffff81293d35>] debug_object_fixup+0x15/0x20
>> [<ffffffff8129450c>] debug_object_activate+0xdc/0x190
>> [<ffffffff81177b50>] ? kmem_cache_shrink+0x70/0x70
>> [<ffffffff810f0d12>] __call_rcu+0x42/0x1e0
>> [<ffffffff810f0ee5>] call_rcu_sched+0x15/0x20
>> [<ffffffff81177113>] slab_destroy+0x153/0x160
>> [<ffffffff81177628>] ? cache_flusharray+0x68/0x180
>> [<ffffffff81177179>] free_block+0x59/0x230
>> [<ffffffff81177655>] cache_flusharray+0x95/0x180
>> [<ffffffff81176dbf>] ? kmem_cache_free+0x11f/0x320
>> [<ffffffff81176f6c>] kmem_cache_free+0x2cc/0x320
>> [<ffffffff8115b5b1>] ? __put_anon_vma+0x61/0xb0
>> [<ffffffff8115b5b1>] __put_anon_vma+0x61/0xb0
>> [<ffffffff8115bb8b>] unlink_anon_vmas+0x13b/0x1a0
>> [<ffffffff8114fac1>] free_pgtables+0x91/0x120
>> [<ffffffff81156101>] exit_mmap+0xb1/0x120
>> [<ffffffff8104e24b>] mmput+0x7b/0x120
>> [<ffffffff81053d68>] exit_mm+0x108/0x130
>> [<ffffffff8153aa70>] ? _raw_spin_unlock_irq+0x30/0x50
>> [<ffffffff81056277>] do_exit+0x167/0x970
>> [<ffffffff811b36c3>] ? mntput+0x23/0x40
>> [<ffffffff81192f6d>] ? fput+0x1ad/0x280
>> [<ffffffff8153ae59>] ? retint_swapgs+0x13/0x1b
>> [<ffffffff81056adb>] do_group_exit+0x5b/0xd0
>> [<ffffffff81056b67>] sys_exit_group+0x17/0x20
>> [<ffffffff81543729>] system_call_fastpath+0x16/0x1b
> --
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