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Date: Wed, 14 May 2014 20:40:59 +0200 From: Oleg Nesterov <oleg@...hat.com> To: David Miller <davem@...emloft.net> Cc: Peter Zijlstra <peterz@...radead.org>, netdev@...r.kernel.org, linux-kernel@...r.kernel.org Subject: net/ && prepare_to_wait_exclusive() Hello, I know almost nothing about networking and of course I do not understand this code. So I can be easily wrong, but (at least) unix_wait_for_peer() looks wrong wrt prepare_to_wait_exclusive(), and ignoring the potential optimizations it needs - finish_wait(&u->peer_wait, &wait); + abort_exclusive_wait(..., TASK_INTERRUPTIBLE, NULL); change? Suppose that unix_recvq_full(X) == true and 2 threads, T1 and T2, are sleeping in unix_dgram_sendmsg(). Another thread does read(X) and this empties ->sk_receive_queue so that the next read(X) will block. We should wake up at least one thread. The reader does wake_up_interruptible_sync_poll() and this is __wake_up_common(nr_exclusive => 1), so this (say) wakes T1 up. Suppose that this wake_up() races with (to simplify) SIGKILL and thus T1 writes nothing and exits. Now, the reader does another read(X) and blocks, ->sk_receive_queue is empty, we have the writer T2 but it is still blocked too? Or I completely misread this code? (On a related note... looks like ___wait_event() is not complicated^W clever enough to implement wait_event_interruptible_exclusive_timeout) 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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