linux-kernel - Re: lots of suspicious RCU traces

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Message-ID: <CAFTL4hw=orRVYzuk8L1aBHCxVD05uT_fdFoRJ_BkihoNd0huJg@mail.gmail.com>
Date:	Fri, 26 Oct 2012 11:44:11 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
	Dave Jones <davej@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	linux-kernel@...r.kernel.org
Subject: Re: lots of suspicious RCU traces

2012/10/25 Sergey Senozhatsky <sergey.senozhatsky@...il.com>:
> On (10/25/12 09:06), Frederic Weisbecker wrote:
>> >> > My understanding is (I may be wrong) that we can schedule() from ptrace chain to
>> >> > some arbitrary task, which will continue its execution from the point where RCU assumes
>> >> > CPU as not idle, while CPU in fact still in idle state -- no one said rcu_idle_exit()
>> >> > (or similar) prior to schedule() call.
>> >>
>> >> Yeah but when we are in syscall_trace_leave(), the CPU shouldn't be in
>> >> RCU idle mode. That's where the bug is. How do you manage to trigger
>> >> this bug?
>> >>
>> >
>> > strace -f <anything>
>>
>> I can't reproduce. Can you send me your config?
>>
>
> sure, attached.

Thanks.

Sergey, Dave,

Does the patch I just sent you fix the issue?

Patch is "[PATCH] rcu: Fix unrecovered RCU user mode in syscall_trace_leave()"

Thanks.
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