Messages in this thread | | | From | (Eric W. Biederman) | Date | Fri, 03 Mar 2017 14:06:30 -0600 | Subject | Re: [PATCH 0/2] fix the traced mt-exec deadlock |
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ebiederm@xmission.com (Eric W. Biederman) writes:
> ebiederm@xmission.com (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
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