From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail6.bemta7.messagelabs.com (mail6.bemta7.messagelabs.com [216.82.255.55]) by kanga.kvack.org (Postfix) with ESMTP id C7DE16B0025 for ; Tue, 17 May 2011 16:47:51 -0400 (EDT) Received: from d01relay04.pok.ibm.com (d01relay04.pok.ibm.com [9.56.227.236]) by e7.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p4HKOenJ012171 for ; Tue, 17 May 2011 16:24:40 -0400 Received: from d01av03.pok.ibm.com (d01av03.pok.ibm.com [9.56.224.217]) by d01relay04.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p4HKln2I077316 for ; Tue, 17 May 2011 16:47:49 -0400 Received: from d01av03.pok.ibm.com (loopback [127.0.0.1]) by d01av03.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p4HGlbP1015783 for ; Tue, 17 May 2011 13:47:38 -0300 From: John Stultz Subject: [PATCH 0/3] v5 Improve task->comm locking situation Date: Tue, 17 May 2011 13:47:40 -0700 Message-Id: <1305665263-20933-1-git-send-email-john.stultz@linaro.org> Sender: owner-linux-mm@kvack.org List-ID: To: LKML Cc: John Stultz , Joe Perches , Michal Nazarewicz , Andy Whitcroft , Jiri Slaby , KOSAKI Motohiro , David Rientjes , Dave Hansen , Andrew Morton , linux-mm@kvack.org Ok. Here's v5. Hopefully this is getting close to something that can be queued for 2.6.40. Since my commit 4614a696bd1c3a9af3a08f0e5874830a85b889d4, the current->comm value could be changed by other threads. This changed the comm locking rules, which previously allowed for unlocked current->comm access, since only the thread itself could change its comm. While this was brought up at the time, it was not considered problematic, as the comm writing was done in such a way that only null or incomplete comms could be read. However, recently folks have made it clear they want to see this issue resolved. So fair enough, as I opened this can of worms, I should work to resolve it and this patchset is my initial attempt. The proposed solution here is to introduce a new spinlock that exclusively protects the comm value. We use it to serialize access via get_task_comm() and set_task_comm(). Since some comm access is open-coded using the task lock, we preserve the task locking in set_task_comm for now. Once all comm access is converted to using get_task_comm, we can clean that up as well. I've also introduced a printk %ptc accessor, which makes the conversion to locked access simpler (as most uses are for printks) as well as a checkpatch rule to try to catch any new current->comm users from being introduced. New in this version: Added a spin_lock_init in copy_process as caught by Jiri. Also tweaked the regex as suggested by Joe. Hopefully this will allow for a smooth transition, where we can slowly fix up the unlocked current->comm access bit by bit, reducing the race window with each patch, while not making the situation any worse then it was yesterday. Thanks for the comments and feedback so far. Any additional comments/feedback would still be appreciated. thanks -john CC: Joe Perches CC: Michal Nazarewicz CC: Andy Whitcroft CC: Jiri Slaby CC: KOSAKI Motohiro CC: David Rientjes CC: Dave Hansen CC: Andrew Morton CC: linux-mm@kvack.org John Stultz (3): comm: Introduce comm_lock spinlock to protect task->comm access printk: Add %ptc to safely print a task's comm checkpatch.pl: Add check for task comm references fs/exec.c | 19 ++++++++++++++++--- include/linux/init_task.h | 1 + include/linux/sched.h | 5 ++--- kernel/fork.c | 1 + lib/vsprintf.c | 24 ++++++++++++++++++++++++ scripts/checkpatch.pl | 7 +++++++ 6 files changed, 51 insertions(+), 6 deletions(-) -- 1.7.3.2.146.gca209 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org