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Message-ID: <509A83F8.6040402@oracle.com>
Date:	Wed, 07 Nov 2012 10:53:28 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	Glauber Costa <glommer@...allels.com>
CC:	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	kamezawa.hiroyu@...fujitsu.com,
	Johannes Weiner <hannes@...xchg.org>,
	Tejun Heo <tj@...nel.org>, Michal Hocko <mhocko@...e.cz>,
	Christoph Lameter <cl@...ux.com>,
	Pekka Enberg <penberg@...nel.org>,
	David Rientjes <rientjes@...gle.com>,
	Pekka Enberg <penberg@...helsinki.fi>,
	Suleiman Souhlal <suleiman@...gle.com>,
	Dave Jones <davej@...hat.com>
Subject: Re: [PATCH v6 28/29] slub: slub-specific propagation changes.

On 11/01/2012 08:07 AM, Glauber Costa wrote:
> SLUB allows us to tune a particular cache behavior with sysfs-based
> tunables.  When creating a new memcg cache copy, we'd like to preserve
> any tunables the parent cache already had.
> 
> This can be done by tapping into the store attribute function provided
> by the allocator. We of course don't need to mess with read-only
> fields. Since the attributes can have multiple types and are stored
> internally by sysfs, the best strategy is to issue a ->show() in the
> root cache, and then ->store() in the memcg cache.
> 
> The drawback of that, is that sysfs can allocate up to a page in
> buffering for show(), that we are likely not to need, but also can't
> guarantee. To avoid always allocating a page for that, we can update the
> caches at store time with the maximum attribute size ever stored to the
> root cache. We will then get a buffer big enough to hold it. The
> corolary to this, is that if no stores happened, nothing will be
> propagated.
> 
> It can also happen that a root cache has its tunables updated during
> normal system operation. In this case, we will propagate the change to
> all caches that are already active.
> 
> Signed-off-by: Glauber Costa <glommer@...allels.com>
> CC: Christoph Lameter <cl@...ux.com>
> CC: Pekka Enberg <penberg@...helsinki.fi>
> CC: Michal Hocko <mhocko@...e.cz>
> CC: Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> CC: Johannes Weiner <hannes@...xchg.org>
> CC: Suleiman Souhlal <suleiman@...gle.com>
> CC: Tejun Heo <tj@...nel.org>
> ---

Hi guys,

This patch is making lockdep angry! *bark bark*

[  351.935003] ======================================================
[  351.937693] [ INFO: possible circular locking dependency detected ]
[  351.939720] 3.7.0-rc4-next-20121106-sasha-00008-g353b62f #117 Tainted: G        W
[  351.942444] -------------------------------------------------------
[  351.943528] trinity-child13/6961 is trying to acquire lock:
[  351.943528]  (s_active#43){++++.+}, at: [<ffffffff812f9e11>] sysfs_addrm_finish+0x31/0x60
[  351.943528]
[  351.943528] but task is already holding lock:
[  351.943528]  (slab_mutex){+.+.+.}, at: [<ffffffff81228a42>] kmem_cache_destroy+0x22/0xe0
[  351.943528]
[  351.943528] which lock already depends on the new lock.
[  351.943528]
[  351.943528]
[  351.943528] the existing dependency chain (in reverse order) is:
[  351.943528]
-> #1 (slab_mutex){+.+.+.}:
[  351.960334]        [<ffffffff8118536a>] lock_acquire+0x1aa/0x240
[  351.960334]        [<ffffffff83a944d9>] __mutex_lock_common+0x59/0x5a0
[  351.960334]        [<ffffffff83a94a5f>] mutex_lock_nested+0x3f/0x50
[  351.960334]        [<ffffffff81256a6e>] slab_attr_store+0xde/0x110
[  351.960334]        [<ffffffff812f820a>] sysfs_write_file+0xfa/0x150
[  351.960334]        [<ffffffff8127a220>] vfs_write+0xb0/0x180
[  351.960334]        [<ffffffff8127a540>] sys_pwrite64+0x60/0xb0
[  351.960334]        [<ffffffff83a99298>] tracesys+0xe1/0xe6
[  351.960334]
-> #0 (s_active#43){++++.+}:
[  351.960334]        [<ffffffff811825af>] __lock_acquire+0x14df/0x1ca0
[  351.960334]        [<ffffffff8118536a>] lock_acquire+0x1aa/0x240
[  351.960334]        [<ffffffff812f9272>] sysfs_deactivate+0x122/0x1a0
[  351.960334]        [<ffffffff812f9e11>] sysfs_addrm_finish+0x31/0x60
[  351.960334]        [<ffffffff812fa369>] sysfs_remove_dir+0x89/0xd0
[  351.960334]        [<ffffffff819e1d96>] kobject_del+0x16/0x40
[  351.960334]        [<ffffffff8125ed40>] __kmem_cache_shutdown+0x40/0x60
[  351.960334]        [<ffffffff81228a60>] kmem_cache_destroy+0x40/0xe0
[  351.960334]        [<ffffffff82b21058>] mon_text_release+0x78/0xe0
[  351.960334]        [<ffffffff8127b3b2>] __fput+0x122/0x2d0
[  351.960334]        [<ffffffff8127b569>] ____fput+0x9/0x10
[  351.960334]        [<ffffffff81131b4e>] task_work_run+0xbe/0x100
[  351.960334]        [<ffffffff81110742>] do_exit+0x432/0xbd0
[  351.960334]        [<ffffffff81110fa4>] do_group_exit+0x84/0xd0
[  351.960334]        [<ffffffff8112431d>] get_signal_to_deliver+0x81d/0x930
[  351.960334]        [<ffffffff8106d5aa>] do_signal+0x3a/0x950
[  351.960334]        [<ffffffff8106df1e>] do_notify_resume+0x3e/0x90
[  351.960334]        [<ffffffff83a993aa>] int_signal+0x12/0x17
[  351.960334]
[  351.960334] other info that might help us debug this:
[  351.960334]
[  351.960334]  Possible unsafe locking scenario:
[  351.960334]
[  351.960334]        CPU0                    CPU1
[  351.960334]        ----                    ----
[  351.960334]   lock(slab_mutex);
[  351.960334]                                lock(s_active#43);
[  351.960334]                                lock(slab_mutex);
[  351.960334]   lock(s_active#43);
[  351.960334]
[  351.960334]  *** DEADLOCK ***
[  351.960334]
[  351.960334] 2 locks held by trinity-child13/6961:
[  351.960334]  #0:  (mon_lock){+.+.+.}, at: [<ffffffff82b21005>] mon_text_release+0x25/0xe0
[  351.960334]  #1:  (slab_mutex){+.+.+.}, at: [<ffffffff81228a42>] kmem_cache_destroy+0x22/0xe0
[  351.960334]
[  351.960334] stack backtrace:
[  351.960334] Pid: 6961, comm: trinity-child13 Tainted: G        W    3.7.0-rc4-next-20121106-sasha-00008-g353b62f #117
[  351.960334] Call Trace:
[  351.960334]  [<ffffffff83a3c736>] print_circular_bug+0x1fb/0x20c
[  351.960334]  [<ffffffff811825af>] __lock_acquire+0x14df/0x1ca0
[  351.960334]  [<ffffffff81184045>] ? debug_check_no_locks_freed+0x185/0x1e0
[  351.960334]  [<ffffffff8118536a>] lock_acquire+0x1aa/0x240
[  351.960334]  [<ffffffff812f9e11>] ? sysfs_addrm_finish+0x31/0x60
[  351.960334]  [<ffffffff812f9272>] sysfs_deactivate+0x122/0x1a0
[  351.960334]  [<ffffffff812f9e11>] ? sysfs_addrm_finish+0x31/0x60
[  351.960334]  [<ffffffff812f9e11>] sysfs_addrm_finish+0x31/0x60
[  351.960334]  [<ffffffff812fa369>] sysfs_remove_dir+0x89/0xd0
[  351.960334]  [<ffffffff819e1d96>] kobject_del+0x16/0x40
[  351.960334]  [<ffffffff8125ed40>] __kmem_cache_shutdown+0x40/0x60
[  351.960334]  [<ffffffff81228a60>] kmem_cache_destroy+0x40/0xe0
[  351.960334]  [<ffffffff82b21058>] mon_text_release+0x78/0xe0
[  351.960334]  [<ffffffff8127b3b2>] __fput+0x122/0x2d0
[  351.960334]  [<ffffffff8127b569>] ____fput+0x9/0x10
[  351.960334]  [<ffffffff81131b4e>] task_work_run+0xbe/0x100
[  351.960334]  [<ffffffff81110742>] do_exit+0x432/0xbd0
[  351.960334]  [<ffffffff811243b9>] ? get_signal_to_deliver+0x8b9/0x930
[  351.960334]  [<ffffffff8117d402>] ? get_lock_stats+0x22/0x70
[  351.960334]  [<ffffffff8117d48e>] ? put_lock_stats.isra.16+0xe/0x40
[  351.960334]  [<ffffffff83a977fb>] ? _raw_spin_unlock_irq+0x2b/0x80
[  351.960334]  [<ffffffff81110fa4>] do_group_exit+0x84/0xd0
[  351.960334]  [<ffffffff8112431d>] get_signal_to_deliver+0x81d/0x930
[  351.960334]  [<ffffffff8117d48e>] ? put_lock_stats.isra.16+0xe/0x40
[  351.960334]  [<ffffffff8106d5aa>] do_signal+0x3a/0x950
[  351.960334]  [<ffffffff811c8b33>] ? rcu_cleanup_after_idle+0x23/0x170
[  351.960334]  [<ffffffff811cc1c4>] ? rcu_eqs_exit_common+0x64/0x3a0
[  351.960334]  [<ffffffff811caa5d>] ? rcu_user_enter+0x10d/0x140
[  351.960334]  [<ffffffff811cc8d5>] ? rcu_user_exit+0xc5/0xf0
[  351.960334]  [<ffffffff8106df1e>] do_notify_resume+0x3e/0x90
[  351.960334]  [<ffffffff83a993aa>] int_signal+0x12/0x17


Thanks,
Sasha
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