From: Oleg Nesterov <oleg@redhat.com>
To: Greg Thelen <gthelen@google.com>
Cc: Jens Axboe <axboe@kernel.dk>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: INFO: suspicious rcu_dereference_check() usage - kernel/pid.c:419 invoked rcu_dereference_check() without protection!
Date: Thu, 11 Nov 2010 23:00:49 +0100 [thread overview]
Message-ID: <20101111220048.GA19979@redhat.com> (raw)
In-Reply-To: <xr93sjz73ar6.fsf@ninji.mtv.corp.google.com>
On 11/11, Greg Thelen wrote:
>
> a) my original report added rcu_read_lock() to sys_ioprio_get() and
> claims that "something" is needed in sys_ioprio_set().
>
> c) http://lkml.org/lkml/2010/10/29/168 added rcu locks to both
> sys_ioprio_get() and sys_ioprio_set() thus addressing the issues
> raised in a). However, I do not see this patch in -mm.
Well, I do not know what happened with this patch, but
> I can resubmit my patch, but want to know if there is a reason that
> http://lkml.org/lkml/2010/10/29/168 did not make it into either -mm
> or linux-next?
I am looking at http://lkml.org/lkml/2010/10/29/168 now, and I think
it should be dropped or you can submit the patch on top of it.
It only adds rcu_read_lock() around of find_task_by_vpid(), but we can
use rcu_read_lock() instead of tasklist_lock.
> d) the sys_ioprio_set() comment indicating that "we can't use
> rcu_read_lock()" needs to be updated to be more clear. I'm not sure
> what this should be updated to, which leads into the next
> sub-topic...
It should be just removed. It doesn't match the reality today.
> e) possibly removing tasklist_lock,
Yes.
> though there seems to be some
> concern that this might introduce task->io_context usage race.
No!
I am sorry for confusion, those ->io_context races are completely
orthogonal to s/tasklist/rcu/.
Oleg.
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prev parent reply other threads:[~2010-11-11 22:07 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-12 7:08 Greg Thelen
2010-11-07 18:20 ` Paul E. McKenney
2010-11-08 15:15 ` Oleg Nesterov
2010-11-09 20:29 ` Paul E. McKenney
2010-11-10 15:55 ` Oleg Nesterov
2010-11-10 16:02 ` Oleg Nesterov
2010-11-11 11:19 ` Jens Axboe
2010-11-11 12:30 ` Oleg Nesterov
2010-11-11 12:39 ` Jens Axboe
2010-11-11 19:45 ` Greg Thelen
2010-11-11 22:00 ` Oleg Nesterov [this message]
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