From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Frederic Weisbecker <fweisbec@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: Wed, 24 Oct 2012 22:50:56 -0700 [thread overview]
Message-ID: <20121025055056.GA2661@swordfish> (raw)
In-Reply-To: <CAFTL4hxmh7yV8ePUhY_7hOuG=JrbZZcNvV88bWcUmwG9X0W04A@mail.gmail.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@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?
>
strace -f <anything>
-ss
next prev parent reply other threads:[~2012-10-25 5:53 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
2012-10-25 5:50 ` Sergey Senozhatsky [this message]
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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