Konstantin Belousov 1d48f121d8 Ensure that when a blockable open of fifo returns success, a valid ... file descriptor opened for complimentary access exists as well. The implementation of the guarantee is done by counting the generations of readers and writers opens. We return success and not EINTR or ERESTART error, when the sleep for complimentary opening is interrupted, but the generation was changed during the sleep. Longer explanation: assume there are two threads, A doing open("fifo", O_RDONLY) and B doing open("fifo", O_WRONLY), and no other threads either trying to open the fifo, nor there are any file descriptors referencing the fifo. Before the change, it was possible e.g. for for thread A to return a valid file descriptor, while thread B returned EINTR if a signal to B was delivered simultaneously with the wakeup from A. After the change, in this situation both A::open() and B::open() succeed and the signal is made "as if" it was noticed slightly later. Note that the signal actual delivery is not changed, it is done by ast on syscall return path, so signal handler is still executed before first instruction after syscall. See PR for the code demonstrating the issue. PR: 203162 Reported by: Victor Stinner victor.stinner@gmail.com Reviewed by: jilles Tested by: bapt, pho Sponsored by: The FreeBSD Foundation MFC after: 1 week		2015-09-20 21:18:33 +00:00
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fifo_vnops.c	Ensure that when a blockable open of fifo returns success, a valid	2015-09-20 21:18:33 +00:00