From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with ESMTP id A9B0690010E for ; Thu, 12 May 2011 19:03:13 -0400 (EDT) Received: from d01relay02.pok.ibm.com (d01relay02.pok.ibm.com [9.56.227.234]) by e1.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p4CMq6Li026879 for ; Thu, 12 May 2011 18:52:06 -0400 Received: from d01av01.pok.ibm.com (d01av01.pok.ibm.com [9.56.224.215]) by d01relay02.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p4CN2tFl444562 for ; Thu, 12 May 2011 19:03:03 -0400 Received: from d01av01.pok.ibm.com (loopback [127.0.0.1]) by d01av01.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p4CN2tuv008711 for ; Thu, 12 May 2011 19:02:55 -0400 From: John Stultz Subject: [PATCH 0/3] v3 Improve task->comm locking situation Date: Thu, 12 May 2011 16:02:48 -0700 Message-Id: <1305241371-25276-1-git-send-email-john.stultz@linaro.org> Sender: owner-linux-mm@kvack.org List-ID: To: LKML Cc: John Stultz , Ted Ts'o , KOSAKI Motohiro , David Rientjes , Dave Hansen , Andrew Morton , linux-mm@kvack.org 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 seqlock 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). And new in this version: I've added a checkpatch rule to try to catch any new current->comm users from being introduced. Although I suspect the script will need some additional work. 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: Ted Ts'o CC: KOSAKI Motohiro CC: David Rientjes CC: Dave Hansen CC: Andrew Morton CC: linux-mm@kvack.org John Stultz (3): comm: Introduce comm_lock seqlock to protect task->comm access printk: Add %ptc to safely print a task's comm checkpatch.pl: Add check for current->comm references fs/exec.c | 25 ++++++++++++++++++++----- include/linux/init_task.h | 1 + include/linux/sched.h | 5 ++--- lib/vsprintf.c | 27 +++++++++++++++++++++++++++ scripts/checkpatch.pl | 4 ++++ 5 files changed, 54 insertions(+), 8 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