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. Now arguably that might be what is desirable but I don't think so. If we aren't ptracing a thread then I don't think we want to delay sending SIGCHLD to the parent. So this whole area of the semantics of a ptrace'd multi-threaded process exiting/exec'ing looks like it needs a thorough going over. 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
