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From: Oleg Nesterov <oleg@redhat.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Don Zickus <dzickus@redhat.com>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Ingo Molnar <mingo@elte.hu>,
	Jerome Marchand <jmarchan@redhat.com>,
	Mandeep Singh Baines <msb@google.com>,
	Roland McGrath <roland@redhat.com>,
	linux-kernel@vger.kernel.org, stable@kernel.org,
	"Eric W. Biederman" <ebiederm@xmission.com>
Subject: Re: while_each_thread() under rcu_read_lock() is broken?
Date: Fri, 25 Jun 2010 11:55:48 +0200	[thread overview]
Message-ID: <20100625095548.GA6292@redhat.com> (raw)
In-Reply-To: <20100625034105.GD2391@linux.vnet.ibm.com>

On 06/24, Paul E. McKenney wrote:
>
> On Thu, Jun 24, 2010 at 11:57:02PM +0200, Oleg Nesterov wrote:
> > On 06/24, Paul E. McKenney wrote:
> > >
> > > 4.	Some other thread might do pthread_exit(), removing itself
> > > 	from the thread group, and again might do so while the hapless
> > > 	reader is referencing that thread.  In this case, we want
> > > 	the hapless reader to continue scanning the remainder of the
> > > 	thread group.
> >
> > Yes.
> >
> > But, if that thread was used as a starting point g, then
> >
> > 	before the patch:	loop forever
> > 	after the patch:	break
>
> So it is OK to skip some of the other threads in this case, even
> though they were present throughout the whole procedure?

I think, yes. We can miss them in any case, they can go away before
while_each_thread(g, t) starts the scan.

If g == group_leader (old or new), then we should notice this thread
at least.

Otherwise we can miss them all, with or without next_thread_careful().

Oleg.


  reply	other threads:[~2010-06-25  9:57 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-06-18 19:02 [PATCH] fix the racy check_hung_uninterruptible_tasks()->rcu_lock_break() logic Oleg Nesterov
2010-06-18 19:34 ` while_each_thread() under rcu_read_lock() is broken? Oleg Nesterov
2010-06-18 21:08   ` Roland McGrath
2010-06-18 22:37     ` Oleg Nesterov
2010-06-18 22:33   ` Paul E. McKenney
2010-06-21 17:09     ` Oleg Nesterov
2010-06-21 17:44       ` Oleg Nesterov
2010-06-21 18:00         ` Oleg Nesterov
2010-06-21 19:02         ` Roland McGrath
2010-06-21 20:06           ` Oleg Nesterov
2010-06-21 21:19             ` Eric W. Biederman
2010-06-22 14:34               ` Oleg Nesterov
2010-07-08 23:59             ` Roland McGrath
2010-07-09  0:41               ` Paul E. McKenney
2010-07-09  1:01                 ` Roland McGrath
2010-07-09 16:18                   ` Paul E. McKenney
2010-06-21 20:51       ` Paul E. McKenney
2010-06-21 21:22         ` Eric W. Biederman
2010-06-21 21:38           ` Paul E. McKenney
2010-06-22 21:23         ` Oleg Nesterov
2010-06-22 22:12           ` Paul E. McKenney
2010-06-23 15:24             ` Oleg Nesterov
2010-06-24 18:07               ` Paul E. McKenney
2010-06-24 18:50                 ` Chris Friesen
2010-06-24 22:00                   ` Oleg Nesterov
2010-06-25  0:08                     ` Eric W. Biederman
2010-06-25  3:42                       ` Paul E. McKenney
2010-06-25 10:08                       ` Oleg Nesterov
2010-07-09  0:52                       ` Roland McGrath
2010-06-24 21:14                 ` Roland McGrath
2010-06-25  3:37                   ` Paul E. McKenney
2010-07-09  0:41                     ` Roland McGrath
2010-06-24 21:57                 ` Oleg Nesterov
2010-06-25  3:41                   ` Paul E. McKenney
2010-06-25  9:55                     ` Oleg Nesterov [this message]
2010-06-28 23:43                       ` Paul E. McKenney
2010-06-29 13:05                         ` Oleg Nesterov
2010-06-29 15:34                           ` Paul E. McKenney
2010-06-29 17:54                             ` Oleg Nesterov
2010-06-19  5:00   ` Mandeep Baines
2010-06-19  5:35     ` Frederic Weisbecker
2010-06-19 15:44       ` Mandeep Baines
2010-06-19 19:19     ` Oleg Nesterov
2010-06-18 20:11 ` [PATCH] fix the racy check_hung_uninterruptible_tasks()->rcu_lock_break() logic Frederic Weisbecker
2010-06-18 20:38 ` Mandeep Singh Baines

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