linux-kernel - Re: while_each_thread() under rcu_read

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Message-ID: <20100624220007.GB21360@redhat.com>
Date:	Fri, 25 Jun 2010 00:00:07 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Chris Friesen <chris.friesen@...band.com>
Cc:	paulmck@...ux.vnet.ibm.com,
	Andrew Morton <akpm@...ux-foundation.org>,
	Don Zickus <dzickus@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Jerome Marchand <jmarchan@...hat.com>,
	Mandeep Singh Baines <msb@...gle.com>,
	Roland McGrath <roland@...hat.com>,
	linux-kernel@...r.kernel.org, stable@...nel.org,
	"Eric W. Biederman" <ebiederm@...ssion.com>
Subject: Re: while_each_thread() under rcu_read_lock() is broken?

On 06/24, Chris Friesen wrote:
>
> On 06/24/2010 12:07 PM, Paul E. McKenney wrote:
>
> > 3.	The thread-group leader might do pthread_exit(), removing itself
> > 	from the thread group -- and might do so while the hapless reader
> > 	is referencing that thread.
> >
> > 	But isn't this prohibited?  Or is it really legal to do a
> > 	pthread_create() to create a new thread and then have the
> > 	parent thread call pthread_exit()?  Not something I would
> > 	consider trying in my own code!  Well, I might, just to
> > 	be perverse, but...  ;-)
>
> I believe SUS allows the main thread to explicitly call pthread_exit(),
> leaving the other threads to run.  If the main() routine just returns
> then it implicitly calls exit().

Correct.

But, to clarify, if the main thread does pthread_exit() (sys_exit,
actually), it won't be removed from the group. It will be zombie
until all other threads exit.

Oleg.

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