Hi (Cc to John Stultz who/proc/<pid>/comm author. I think we need to hear his opinion) > On Tue, 2011-04-19 at 14:21 -0700, David Rientjes wrote: > > On Tue, 19 Apr 2011, KOSAKI Motohiro wrote: > > > The rule is, > > > > > > 1) writing comm > > > need task_lock > > > 2) read _another_ thread's comm > > > need task_lock > > > 3) read own comm > > > no need task_lock > > > > That was true a while ago, but you now need to protect every thread's > > ->comm with get_task_comm() or ensuring task_lock() is held to protect > > against /proc/pid/comm which can change other thread's ->comm. That was > > different before when prctl(PR_SET_NAME) would only operate on current, so > > no lock was needed when reading current->comm. > > Everybody still goes through set_task_comm() to _set_ it, though. That > means that the worst case scenario that we get is output truncated > (possibly to nothing). We already have at least one existing user in > mm/ (kmemleak) that thinks this is OK. I'd tend to err in the direction > of taking a truncated or empty task name to possibly locking up the > system. > > There are also plenty of instances of current->comm going in to the > kernel these days. I count 18 added since 2.6.37. > > As for a long-term fix, locks probably aren't the answer. Would > something like this completely untested patch work? It would have the > added bonus that it keeps tsk->comm users working for the moment. We > could eventually add an rcu_read_lock()-annotated access function. The concept is ok to me. but AFAIK some caller are now using ARRAY_SIZE(tsk->comm). or sizeof(tsk->comm). Probably callers need to be changed too. Thanks. -- 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>