Re: [PATCH 1/3] comm: Introduce comm_lock seqlock to protect task->comm access

David Rientjes
2011-05-12T22:00:58Z

On Tue, 10 May 2011, John Stultz wrote:

> The implicit rules for current->comm access being safe without locking
> are no longer true. Accessing current->comm without holding the task
> lock may result in null or incomplete strings (however, access won't
> run off the end of the string).
>
> In order to properly fix this, I've introduced a comm_lock seqlock
> which will protect comm access and modified get_task_comm() and
> set_task_comm() to use it.
>
> Since there are a number of cases where comm access is open-coded
> safely grabbing the task_lock(), we preserve the task locking in
> set_task_comm, so those users are also safe.
>
> With this patch, users that access current->comm without a lock
> are still prone to null/incomplete comm strings, but it should
> be no worse then it is now.
>
> The next step is to go through and convert all comm accesses to
> use get_task_comm(). This is substantial, but can be done bit by
> bit, reducing the race windows with each patch.
>
> CC: Ted Ts'o <tytso@mit.edu>
> CC: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> CC: David Rientjes <rientjes@google.com>
> CC: Dave Hansen <dave@linux.vnet.ibm.com>
> CC: Andrew Morton <akpm@linux-foundation.org>
> CC: linux-mm@kvack.org
> Signed-off-by: John Stultz <john.stultz@linaro.org>

Acked-by: David Rientjes <rientjes@google.com>