linux-kernel - Re: lots of suspicious RCU traces

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Message-ID: <CAFTL4hxM8KqL3=GLkJDU-9pKVHrb1nSoDgFx8UVB7F7tryw6HA@mail.gmail.com>
Date:	Thu, 25 Oct 2012 09:06:36 +0200
From:	Frederic Weisbecker <fweisbec@...il.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, Dave Jones <davej@...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 00:32), Frederic Weisbecker wrote:
>> First of all, thanks a lot for your report.
>>
>> 2012/10/24 Sergey Senozhatsky <sergey.senozhatsky@...il.com>:
>> > On (10/24/12 20:06), Oleg Nesterov wrote:
>> >> On 10/24, Sergey Senozhatsky wrote:
>> >> >
>> >> > small question,
>> >> >
>> >> > ptrace_notify() and forward calls are able to both indirectly and directly call schedule(),
>> >> > /* direct call from ptrace_stop()*/,
>> >> > should, in this case, rcu_user_enter() be called before tracehook_report_syscall_exit(regs, step)
>> >> > and ptrace chain?
>> >>
>> >> Well, I don't really understand this magic... but why?
>> >>
>> >
>> > 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?

Thanks.
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