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From: Roland McGrath <roland@redhat.com>
To: Oleg Nesterov <oleg@redhat.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>,
	linux-kernel@vger.kernel.org, stable@kernel.org,
	"Eric W. Biederman" <ebiederm@xmission.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Subject: Re: while_each_thread() under rcu_read_lock() is broken?
Date: Fri, 18 Jun 2010 14:08:01 -0700 (PDT)	[thread overview]
Message-ID: <20100618210801.61B4540162@magilla.sf.frob.com> (raw)
In-Reply-To: Oleg Nesterov's message of  Friday, 18 June 2010 21:34:03 +0200 <20100618193403.GA17314@redhat.com>

I think you're right.  I can't see what would prevent that race.  

So for_each_process and do_each_thread are safe only under
read_lock(&tasklist_lock) and while_each_thread is only safe under
either that or siglock.  (Also a few places using next_thread in
similar loops outside those macros.)

Perhaps we could move those del's from __unhash_process to
__put_task_struct (or just delayed_put_task_struct?) and then
they wouldn't need to be rculist.h calls after all.  But we
would a need careful audit to figure out the assumptions about
being on the list meaning not reaped yet.

I think de_thread() in exec-by-nonleader is the only case where this
can happen, right?  So then perhaps we could make it call release_task
only via call_rcu?


Thanks,
Roland

  reply	other threads:[~2010-06-18 21:08 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 [this message]
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
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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