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Date: Wed, 5 Feb 2014 20:05:51 -0800 (PST)
From: David Rientjes <rientjes@google.com>
X-X-Sender: rientjes@chino.kir.corp.google.com
To: Steven Rostedt <rostedt@goodmis.org>
cc: LKML <linux-kernel@vger.kernel.org>, penberg@kernel.org, cl@linux.com,
        Andrew Morton <akpm@linux-foundation.org>,
        Vladimir Davydov <vdavydov@parallels.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH v2] slub: Do not assert not having lock in removing freed
 partial
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On Wed, 5 Feb 2014, Steven Rostedt wrote:

> Vladimir reported the following issue:
> 
> Commit c65c1877bd68 ("slub: use lockdep_assert_held") requires
> remove_partial() to be called with n->list_lock held, but free_partial()
> called from kmem_cache_close() on cache destruction does not follow this
> rule, leading to a warning:
> 
>   WARNING: CPU: 0 PID: 2787 at mm/slub.c:1536 __kmem_cache_shutdown+0x1b2/0x1f0()
>   Modules linked in:
>   CPU: 0 PID: 2787 Comm: modprobe Tainted: G        W    3.14.0-rc1-mm1+ #1
>   Hardware name:
>    0000000000000600 ffff88003ae1dde8 ffffffff816d9583 0000000000000600
>    0000000000000000 ffff88003ae1de28 ffffffff8107c107 0000000000000000
>    ffff880037ab2b00 ffff88007c240d30 ffffea0001ee5280 ffffea0001ee52a0
>   Call Trace:
>    [<ffffffff816d9583>] dump_stack+0x51/0x6e
>    [<ffffffff8107c107>] warn_slowpath_common+0x87/0xb0
>    [<ffffffff8107c145>] warn_slowpath_null+0x15/0x20
>    [<ffffffff811c7fe2>] __kmem_cache_shutdown+0x1b2/0x1f0
>    [<ffffffff811908d3>] kmem_cache_destroy+0x43/0xf0
>    [<ffffffffa013a123>] xfs_destroy_zones+0x103/0x110 [xfs]
>    [<ffffffffa0192b54>] exit_xfs_fs+0x38/0x4e4 [xfs]
>    [<ffffffff811036fa>] SyS_delete_module+0x19a/0x1f0
>    [<ffffffff816dfcd8>] ? retint_swapgs+0x13/0x1b
>    [<ffffffff810d2125>] ? trace_hardirqs_on_caller+0x105/0x1d0
>    [<ffffffff81359efe>] ? trace_hardirqs_on_thunk+0x3a/0x3f
>    [<ffffffff816e8539>] system_call_fastpath+0x16/0x1b
> 
> 
> His solution was to add a spinlock in order to quiet lockdep. Although
> there would be no contention to adding the lock, that lock also
> requires disabling of interrupts which will have a larger impact on the
> system.
> 
> Instead of adding a spinlock to a location where it is not needed for
> lockdep, make a __remove_partial() function that does not test if
> the list_lock is held, as no one should have it due to it being freed.
> 
> Also added a __add_partial() function that does not do the lock validation
> either, as it is not needed for the creation of the cache.
> 
> Suggested-by: David Rientjes <rientjes@google.com>
> Reported-by: Vladimir Davydov <vdavydov@parallels.com>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Acked-by: David Rientjes <rientjes@google.com>

Thanks Steven!