From: Peter Zijlstra <peterz@infradead.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched: RCU-protect __set_task_cpu() in set_task_cpu()
Date: Tue, 31 May 2011 21:45:46 +0200 [thread overview]
Message-ID: <1306871146.2497.590.camel@laptop> (raw)
In-Reply-To: <20110531172651.GA4478@swordfish.minsk.epam.com>
On Tue, 2011-05-31 at 20:26 +0300, Sergey Senozhatsky wrote:
> Wrap __set_task_cpu() with RCU read-side critical section.
> __set_task_cpu() calls task_group() that performs rcu dereference check in
> task_subsys_state_check(), causing:
>
> [ 152.262791] kernel/sched.c:619 invoked rcu_dereference_check() without protection!
> [ 152.262795]
> [ 152.262841] stack backtrace:
> [ 152.262846] Pid: 16, comm: watchdog/1 Not tainted 3.0.0-rc1-dbg-00441-g1d5f9cc-dirty #599
> [ 152.262851] Call Trace:
> [ 152.262860] [<ffffffff8106e17b>] lockdep_rcu_dereference+0xa7/0xaf
> [ 152.262868] [<ffffffff810369f4>] set_task_cpu+0x1ed/0x3ce
> [ 152.262876] [<ffffffff8123a5d7>] ? plist_check_head+0x94/0x98
> [ 152.262883] [<ffffffff8123a72d>] ? plist_del+0x82/0x89
> [ 152.262889] [<ffffffff8102b139>] ? dequeue_task_rt+0x33/0x38
> [ 152.262895] [<ffffffff8102e3ac>] ? dequeue_task+0x82/0x89
> [ 152.262902] [<ffffffff81036fc0>] push_rt_task.part.131+0x1bb/0x247
> [ 152.262909] [<ffffffff81037138>] post_schedule_rt+0x1b/0x24
> [ 152.262918] [<ffffffff81477c1c>] schedule+0x989/0xa9e
> [ 152.262923] [<ffffffff814775e6>] ? schedule+0x353/0xa9e
> [ 152.262931] [<ffffffff8147de58>] ? sub_preempt_count+0x8f/0xa3
> [ 152.262938] [<ffffffff8109fd2c>] ? watchdog_enable+0x195/0x195
> [ 152.262946] [<ffffffff810072e5>] ? native_sched_clock+0x38/0x65
> [ 152.262953] [<ffffffff81062c0c>] ? cpu_clock+0x4a/0x5f
> [ 152.262958] [<ffffffff8109fd2c>] ? watchdog_enable+0x195/0x195
> [ 152.262965] [<ffffffff81071a15>] ? trace_hardirqs_on_caller+0x10d/0x131
> [ 152.262971] [<ffffffff81071a46>] ? trace_hardirqs_on+0xd/0xf
> [ 152.262977] [<ffffffff8109fd2c>] ? watchdog_enable+0x195/0x195
> [ 152.262983] [<ffffffff8109fd94>] watchdog+0x68/0xab
> [ 152.262990] [<ffffffff8105cb82>] kthread+0x9a/0xa2
> [ 152.262999] [<ffffffff81481e24>] kernel_thread_helper+0x4/0x10
> [ 152.263005] [<ffffffff8102d6bf>] ? finish_task_switch+0x76/0xf0
> [ 152.263012] [<ffffffff8147b258>] ? retint_restore_args+0x13/0x13
> [ 152.263019] [<ffffffff8105cae8>] ? __init_kthread_worker+0x53/0x53
> [ 152.263024] [<ffffffff81481e20>] ? gs_change+0x13/0x13
>
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Sorry, no. You failed to ask youself, what is it protecting, and how
does wrapping it like this ensure the proper thing is done.
What you've done is basically silence the warning for all set_task_cpu()
callers, without proper consideration.
next prev parent reply other threads:[~2011-05-31 19:42 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-05-31 17:26 [PATCH] sched: RCU-protect __set_task_cpu() in set_task_cpu() Sergey Senozhatsky
2011-05-31 19:45 ` Peter Zijlstra [this message]
2011-06-03 15:37 ` Peter Zijlstra
2011-06-03 18:16 ` Sergey Senozhatsky
2011-06-03 22:49 ` Sergey Senozhatsky
2011-06-05 19:12 ` Oleg Nesterov
2011-06-06 9:06 ` Peter Zijlstra
2011-06-06 16:46 ` Oleg Nesterov
2011-06-07 9:31 ` Peter Zijlstra
2011-06-07 14:03 ` Oleg Nesterov
2011-06-06 13:43 ` Peter Zijlstra
2011-06-07 12:03 ` [tip:sched/urgent] sched: Fix/clarify set_task_cpu() locking rules tip-bot for Peter Zijlstra
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