From: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Dave Jones <davej@redhat.com>,
Frederic Weisbecker <fweisbec@gmail.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 11:21:11 -0700 [thread overview]
Message-ID: <20121024182111.GA2340@swordfish> (raw)
In-Reply-To: <20121024180608.GA22840@redhat.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.
if so, does the same apply to in_user?
-ss
> Until we return to user-mode this CPU should be in "in_user = false" state.
>
> I am not sure I understand how it is guaranteed that rcu_user_exit() was
> called... probably TIF_NOHZ should trigger the slow path and ensure that
> syscall_trace_enter()->rcu_user_exit() will be called.
>
> Oleg.
>
next prev parent reply other threads:[~2012-10-24 18:23 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 [this message]
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
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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