ebiederm@xxxxxxxxxxxx (Eric W. Biederman) writes: > ebiederm@xxxxxxxxxxxx (Eric W. Biederman) writes: > >> The big lesson for me, and what was not obvious from your change >> description is that we are changing the user space visible semantics >> of exec+ptrace and that cred_guard_mutex is not at all the problem (as >> we always take cred_guard_mutex in a killable or interruptible way). > > Just to follow up. > > Because the cred_guard_mutex is fine as is we don't need to move > de_thread out from under cred_guard_mutex. We just need to change > de_thread to wait until all of the other threads are zombies. > Which should remove about half your proposed patch. > > The other key thing is that knowning it isn't cred_guard_mutex let's us > know that this kind of deadlock goes all of the way back to when > CLONE_THREAD was merged into the kernel. > > Insteresingly enough looking at zap_other_threads and notify_count I > have found a second bug. When a multi-threaded processes becomes a > zombie we don't send the notification to the parent process until the > non-leader threads have been reaped. Which means ptrace can mess up > sending SIGCHLD to the parent. Bah. I was misreading the code. Nothing but exec uses notify_count and group_exit_task. Eric -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
