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 <redacted>
CC: Christoph Lameter <redacted>
CC: Pekka Enberg <redacted>
CC: Michal Hocko <redacted>
CC: Kamezawa Hiroyuki <redacted>
CC: Johannes Weiner <hannes@cmpxchg.org>
CC: Suleiman Souhlal <redacted>
CC: Tejun Heo <tj@kernel.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