From: Jens Axboe <axboe@kernel.dk>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Greg Thelen <gthelen@google.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 12:19:08 +0100 [thread overview]
Message-ID: <4CDBD12C.4010807@kernel.dk> (raw)
In-Reply-To: <20101110160211.GA2562@redhat.com>
On 2010-11-10 17:02, Oleg Nesterov wrote:
> (another try with the proper email address)
>
> On 11/09, Paul E. McKenney wrote:
>>
>> Thank you, Oleg! Greg, would you be willing to update your patch
>> to remove the comment? (Perhaps tasklist_lock as well...)
>
> Agreed, I think tasklock should be killed.
>
>
> But wait. Whatever we do, isn't this code racy? I do not see why, say,
> sys_ioprio_set(IOPRIO_WHO_PROCESS) can't install ->io_context after
> this task has already passed exit_io_context().
>
> Jens, am I missed something?
Not sure, I think the original intent was for the tasklist_lock to
protect from a concurrent exit, but that looks like nonsense and it was
just there to protect the task lookup.
How about moving the ->io_context check and exit_io_context() in
do_exit() under the task lock? Coupled with a check for PF_EXITING in
set_task_ioprio().
--
Jens Axboe
WARNING: multiple messages have this Message-ID (diff)
From: Jens Axboe <axboe@kernel.dk>
To: Oleg Nesterov <oleg@redhat.com>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Greg Thelen <gthelen@google.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 12:19:08 +0100 [thread overview]
Message-ID: <4CDBD12C.4010807@kernel.dk> (raw)
In-Reply-To: <20101110160211.GA2562@redhat.com>
On 2010-11-10 17:02, Oleg Nesterov wrote:
> (another try with the proper email address)
>
> On 11/09, Paul E. McKenney wrote:
>>
>> Thank you, Oleg! Greg, would you be willing to update your patch
>> to remove the comment? (Perhaps tasklist_lock as well...)
>
> Agreed, I think tasklock should be killed.
>
>
> But wait. Whatever we do, isn't this code racy? I do not see why, say,
> sys_ioprio_set(IOPRIO_WHO_PROCESS) can't install ->io_context after
> this task has already passed exit_io_context().
>
> Jens, am I missed something?
Not sure, I think the original intent was for the tasklist_lock to
protect from a concurrent exit, but that looks like nonsense and it was
just there to protect the task lookup.
How about moving the ->io_context check and exit_io_context() in
do_exit() under the task lock? Coupled with a check for PF_EXITING in
set_task_ioprio().
--
Jens Axboe
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next prev parent reply other threads:[~2010-11-11 11:19 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-10-12 7:08 INFO: suspicious rcu_dereference_check() usage - kernel/pid.c:419 invoked rcu_dereference_check() without protection! Greg Thelen
2010-10-12 7:08 ` Greg Thelen
2010-11-07 18:20 ` Paul E. McKenney
2010-11-07 18:20 ` Paul E. McKenney
2010-11-08 15:15 ` Oleg Nesterov
2010-11-08 15:15 ` Oleg Nesterov
2010-11-09 20:29 ` Paul E. McKenney
2010-11-09 20:29 ` Paul E. McKenney
2010-11-10 15:55 ` Oleg Nesterov
2010-11-10 15:55 ` Oleg Nesterov
2010-11-10 16:02 ` Oleg Nesterov
2010-11-10 16:02 ` Oleg Nesterov
2010-11-11 11:19 ` Jens Axboe [this message]
2010-11-11 11:19 ` Jens Axboe
2010-11-11 12:30 ` Oleg Nesterov
2010-11-11 12:30 ` Oleg Nesterov
2010-11-11 12:39 ` Jens Axboe
2010-11-11 12:39 ` Jens Axboe
2010-11-11 19:45 ` Greg Thelen
2010-11-11 19:45 ` Greg Thelen
2010-11-11 22:00 ` Oleg Nesterov
2010-11-11 22:00 ` Oleg Nesterov
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