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Date: Wed, 24 Oct 2012 12:17:16 -0700
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
Message-ID: <20121024191716.GB2340@swordfish>
References: <20121017034918.GA13295@redhat.com>
 <20121024164235.GA2467@swordfish>
 <20121024180608.GA22840@redhat.com>
 <20121024182111.GA2340@swordfish>
 <20121024185230.GB5025@redhat.com>
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On (10/24/12 20:52), Oleg Nesterov wrote:
> On 10/24, Sergey Senozhatsky wrote:
> >
> > 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)
> 
> Oh, I bet I have much more chances to be wrong ;)
> 
> > that we can schedule() from ptrace chain to
> 
> I don't understand how ptrace chain differs from, say, audit_syscall_exit().
> There is nothing special in ptrace_stop() in this respect.
>

hm.

> > 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()
> 
> confused... of course it would be wrong if syscall_trace_leave() is
> called when CPU is considered idle,
> 

sorry, I meant idle from RCU point of view:

int rcu_is_cpu_idle(void)                                                                                                                                                                                                      
{
         return !rcu_dynticks_nesting;
}



> > if so, does the same apply to in_user?
> 
> Not sure we understand each other. But I believe that ->in_user should be
> already false when syscall_trace_leave() is called.
>

oh, my apology. I was very wrong about this.

	-ss

> 
> Oleg.
>