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. In addition, with this new patch set I've introduced a printk %ptc accessor, which makes the conversion to locked access simpler (as most uses are for printks). 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. Also in this patch set I have a an example how I've converted comm access in ext4 to use %ptc method. I've got quite a number of similar patches queued, but wanted to get some feedback on the approach before I start patchbombing everyone. Comments/feedback would be appreciated. thanks -john CC: Ted Ts'o <tytso@xxxxxxx> CC: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> CC: David Rientjes <rientjes@xxxxxxxxxx> CC: Dave Hansen <dave@xxxxxxxxxxxxxxxxxx> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> CC: linux-mm@xxxxxxxxx John Stultz (3): comm: Introduce comm_lock seqlock to protect task->comm access printk: Add %ptc to safely print a task's comm comm: ext4: Protect task->comm access by using get_task_comm() fs/exec.c | 25 ++++++++++++++++++++----- fs/ext4/file.c | 4 ++-- fs/ext4/super.c | 8 ++++---- include/linux/init_task.h | 1 + include/linux/sched.h | 5 ++--- lib/vsprintf.c | 27 +++++++++++++++++++++++++++ 6 files changed, 56 insertions(+), 14 deletions(-) -- 1.7.3.2.146.gca209 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>