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Date: Mon, 03 Mar 2014 17:43:11 -0500
From: Sasha Levin <sasha.levin@...cle.com>
To: Tejun Heo <tj@...nel.org>
CC: lizefan@...wei.com, containers@...ts.linux-foundation.org,
cgroups@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] cgroup: missing rcu read lock around task_css_set
On 03/03/2014 05:33 PM, Tejun Heo wrote:
> On Sat, Mar 01, 2014 at 10:00:11PM -0500, Sasha Levin wrote:
>> rcu read lock should be held when calling and working with task_css_set.
>>
>> This patch also fixes a related lockdep warning.
>
> Hmmm... PF_EXITING should be visible at that point and cset can't
> change anymore. We prolly need to update lockdep annotation rather
> than adding spurious rcu locking around it. Against which branch is
> it? Can you please post the lockdep warning?
I see it on -next.
[ 0.370543] ===============================
[ 0.371030] [ INFO: suspicious RCU usage. ]
[ 0.371453] 3.14.0-rc4-next-20140303-sasha-00012-g35a2897-dirty #43 Not tainted
[ 0.372223] -------------------------------
[ 0.372627] include/linux/cgroup.h:692 suspicious rcu_dereference_check() usage!
[ 0.373417]
[ 0.373417] other info that might help us debug this:
[ 0.373417]
[ 0.374223]
[ 0.374223] rcu_scheduler_active = 1, debug_locks = 1
[ 0.374993] no locks held by swapper/0/0.
[ 0.375422]
[ 0.375422] stack backtrace:
[ 0.375865] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 3.14.0-rc4-next-20140303-sasha-00012-g35a2897-dirty #43
[ 0.376936] 0000000000000001 ffffffff85e01d58 ffffffff8446a933 0000000000000001
[ 0.377753] ffffffff85e2e4a0 ffffffff85e01d88 ffffffff811a6ddb 0000000000000000
[ 0.380550] ffff88052a2398a8 ffff88052a238000 0000000000000000 ffffffff85e01de8
[ 0.381370] Call Trace:
[ 0.381641] [<ffffffff8446a933>] dump_stack+0x52/0x7f
[ 0.382261] [<ffffffff811a6ddb>] lockdep_rcu_suspicious+0x10b/0x120
[ 0.382893] [<ffffffff8120024d>] cgroup_exit+0x20d/0x250
[ 0.383566] [<ffffffff811dc075>] ? ktime_get_ts+0x145/0x1d0
[ 0.384221] [<ffffffff8113fd66>] copy_process+0x5d6/0x670
[ 0.384850] [<ffffffff8114049b>] do_fork+0x8b/0x2e0
[ 0.385347] [<ffffffff811a9c0d>] ? trace_hardirqs_on+0xd/0x10
[ 0.386009] [<ffffffff8446d47e>] ? mutex_unlock+0xe/0x10
[ 0.386559] [<ffffffff872a4117>] ? early_idt_handlers+0x117/0x120
[ 0.387327] [<ffffffff81140776>] kernel_thread+0x26/0x30
[ 0.387947] [<ffffffff844606a6>] rest_init+0x26/0x150
[ 0.388491] [<ffffffff872a538d>] start_kernel+0x3c0/0x3c7
[ 0.389126] [<ffffffff872a4dfb>] ? repair_env_string+0x5b/0x5b
[ 0.389813] [<ffffffff84468dcb>] ? memblock_reserve+0x49/0x4e
[ 0.390019] [<ffffffff872a43d9>] x86_64_start_reservations+0x2a/0x2c
[ 0.390754] [<ffffffff872a45ae>] x86_64_start_kernel+0x186/0x195
Thanks,
Sasha
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