From: Frederic Weisbecker <fweisbec@gmail.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Dave Jones <davej@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Serge Hallyn <serge.hallyn@canonical.com>,
linux-kernel@vger.kernel.org
Subject: Re: lots of suspicious RCU traces
Date: Thu, 25 Oct 2012 00:32:14 +0200 [thread overview]
Message-ID: <CAFTL4hxmh7yV8ePUhY_7hOuG=JrbZZcNvV88bWcUmwG9X0W04A@mail.gmail.com> (raw)
In-Reply-To: <20121024182111.GA2340@swordfish>
First of all, thanks a lot for your report.
2012/10/24 Sergey Senozhatsky <sergey.senozhatsky@gmail.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?
>
> if so, does the same apply to in_user?
next prev parent reply other threads:[~2012-10-24 22:32 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-17 3:49 lots of suspicious RCU traces Dave Jones
2012-10-24 16:42 ` Sergey Senozhatsky
2012-10-24 18:06 ` Oleg Nesterov
2012-10-24 18:21 ` Sergey Senozhatsky
2012-10-24 18:52 ` Oleg Nesterov
2012-10-24 19:17 ` Sergey Senozhatsky
2012-10-24 19:41 ` Paul E. McKenney
2012-10-24 19:50 ` Sergey Senozhatsky
2012-10-24 20:11 ` Paul E. McKenney
2012-10-24 20:15 ` Sergey Senozhatsky
2012-10-24 22:32 ` Frederic Weisbecker [this message]
2012-10-25 5:50 ` Sergey Senozhatsky
2012-10-25 7:06 ` Frederic Weisbecker
2012-10-25 7:41 ` Sergey Senozhatsky
2012-10-26 9:40 ` [PATCH] rcu: Fix unrecovered RCU user mode in syscall_trace_leave() Frederic Weisbecker
2012-10-26 9:44 ` lots of suspicious RCU traces Frederic Weisbecker
2012-10-26 11:16 ` Sergey Senozhatsky
2012-10-26 15:16 ` Dave Jones
2012-10-25 5:55 ` Sergey Senozhatsky
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