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Date: Tue, 26 Jun 2007 15:54:49 +0400 From: Oleg Nesterov <oleg@...sign.ru> To: Satyam Sharma <satyam.sharma@...il.com> Cc: Jeff Layton <jlayton@...hat.com>, Herbert Xu <herbert@...dor.apana.org.au>, linux-kernel@...r.kernel.org, netdev@...r.kernel.org, "Eric W. Biederman" <ebiederm@...ssion.com> Subject: Re: [PATCH] RFC: have tcp_recvmsg() check kthread_should_stop() and treat it as if it were signalled On 06/26, Satyam Sharma wrote: > > Yes, why not embed a send_sig(SIGKILL) just before the wake_up_process() > in kthread_stop() itself? Personally, I don't think we should do this. kthread_stop() doesn't always mean "kill this thread asap". Suppose that CPU_DOWN does kthread_stop(workqueue->thread) but doesn't flush the queue before that (we did so before 2.6.22 and perhaps we will do again). Now work_struct->func() doing tcp_recvmsg() or wait_event_interruptible() fails, but this is probably not that we want. > So could we have signals in _addition_ to kthread_stop_info and change > kthread_should_stop() to check for both: > > kthread_stop_info.k == current && signal_pending(current) No, this can't work in general. Some kthreads do flush_signals/dequeue_signal, so TIF_SIGPENDING can be lost anyway. I personally think Jeff's idea to use force_sig() is right. kthread_create() doesn't use CLONE_SIGHAND, so it is safe to change ->sighand->actionp[]. (offtopic) cifs_mount: send_sig(SIGKILL,srvTcp->tsk,1); tsk = srvTcp->tsk; if(tsk) kthread_stop(tsk); This "if(tsk)" looks wrong to me. Can srvTcp->tsk be NULL? If yes, send_sig() is not safe. Can srvTcp->tsk become NULL after send_sig() ? If yes, this check is racy, and kthread_stop() is not safe. Oleg. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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