On 10/16, Eric Wong wrote: > > Oleg Nesterov <o...@redhat.com> wrote: > > Yes. Before that 971316f0503a hack epoll can't even know if the task > > which did signalfd_poll() exits and frees the active signalfd_wqh. > > If for example that task forked a child before exit. > > > > And the whole RCU logic is only needed if exit/ep_remove_wait_queue > > actually race with each other. > > Is there any chance this oops is caused by (or at least more easily > exposed by) commit 91cf5ab60ff82ecf4550a596867787c1e360dd3f ? > (epoll: add a reschedule point in ep_free()) > > I thought 91cf5ab would be benign, except... > > > Yes, ugly, agreed. d80e731ecab4 even tries to docunent that this all > > is the hack. > > .. the following sentence from d80e731ecab4 caught my eye: > > It also assumes that nobody can take tasklist_lock under epoll > locks, this seems to be true.
This just reminds that with this patch __wake_up/ep_poll_callback can be called under write_lock(tasklist). > I haven't been able to trace if cond_resched() can take tasklist_lock. No, it can't hold the non-sleepable rwlock_t. And the sentence above doesn't mean the locks like epmutex, it is mostlt about ep->lock. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
