From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>, Dave Jones <davej@redhat.com>,
Frederic Weisbecker <fweisbec@gmail.com>,
Serge Hallyn <serge.hallyn@canonical.com>,
linux-kernel@vger.kernel.org
Subject: Re: lots of suspicious RCU traces
Date: Wed, 24 Oct 2012 13:11:17 -0700 [thread overview]
Message-ID: <20121024201117.GJ2465@linux.vnet.ibm.com> (raw)
In-Reply-To: <20121024195033.GC2340@swordfish>
On Wed, Oct 24, 2012 at 12:50:33PM -0700, Sergey Senozhatsky wrote:
> On (10/24/12 12:41), Paul E. McKenney wrote:
> > On Wed, Oct 24, 2012 at 12:17:16PM -0700, Sergey Senozhatsky wrote:
> > > 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;
> > > }
> >
> > Hmmm... This reproduces on UP builds, then?
>
> I'll compile UP build (will offlining of N-1 CPUs do the trick?).
Oh -- you quoted the Tiny RCU (CONFIG_SMP=n) variant of rcu_is_cpu_idle(),
so I just thought that you were reproducing on CONFIG_SMP=n. You would
have to actually rebuild the kernel to get the different version.
But never mind! RCU_USER_QS depends on CONFIG_SMP=y, so my question
was irrelevant.
Thanx, Paul
> -ss
>
> > > > > 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.
> >
> > Frederic, thoughts?
> >
> > Thanx, Paul
> >
>
next prev parent reply other threads:[~2012-10-24 20:12 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 [this message]
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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