linux-kernel - Re: lots of suspicious RCU traces

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Date:	Wed, 24 Oct 2012 20:06:08 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Cc:	Dave Jones <davej@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.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

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?

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.

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