Date: Thu, 10 Nov 2011 12:30:14 GMT From: Gleb Smirnoff <glebius@FreeBSD.org> To: freebsd-bugs@FreeBSD.org Subject: Re: kern/162379: When select(2) closed writing pipe, it will sticks. Message-ID: <201111101230.pAACUEND066456@freefall.freebsd.org>
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The following reply was made to PR kern/162379; it has been noted by GNATS.
From: Gleb Smirnoff <glebius@FreeBSD.org>
To: Yui NARUSE <naruse@airemix.jp>
Cc: freebsd-gnats-submit@FreeBSD.org
Subject: Re: kern/162379: When select(2) closed writing pipe, it will sticks.
Date: Thu, 10 Nov 2011 16:27:37 +0400
On Tue, Nov 08, 2011 at 04:57:50PM +0000, Yui NARUSE wrote:
Y> >How-To-Repeat:
Y> Run following program, it will sticks.
Y>
Y> #include <stdio.h>
Y> #include <stdlib.h>
Y> #include <errno.h>
Y> #include <sys/select.h>
Y> #define max(x,y) ((x > y) ? x : y)
Y> int
Y> main(void) {
Y> int pipes[2];
Y> int res = pipe(pipes);
Y> if (res != 0) abort();
Y> int r = pipes[0];
Y> int w = pipes[1];
Y> res = close(w);
Y> if (res != 0) abort();
Y> fd_set readfds; FD_ZERO(&readfds);
Y> fd_set writefds; FD_ZERO(&writefds);
Y> fd_set exceptfds; FD_ZERO(&exceptfds);
Y> FD_SET(w, &writefds);
Y> res = select(max(r,w)+1, &readfds, &writefds, &exceptfds, NULL);
Y> if (res) perror("select");
Y> return 0;
Y> }
Y> >Fix:
According to SUS, issuing close() on a descriptor means deallocating it,
and the argument value for close() is not a valid descriptor anymore
after close().
http://pubs.opengroup.org/onlinepubs/9699919799/functions/close.html
So, you are passing an invalid descriptor to FD_SET(). Behavior in this
case is undefined. Quoting SUS:
"The behavior of these macros is undefined if the fd argument is less than 0 or greater than or equal to FD_SETSIZE, or if fd is not a valid file descriptor, or if any of the arguments are expressions with side-effects."
also
"The pselect() and select() functions shall support regular files, terminal and pseudo-terminal devices, STREAMS-based files, FIFOs, pipes, and sockets. The behavior of pselect() and select() on file descriptors that refer to other types of file is unspecified."
More info here:
http://pubs.opengroup.org/onlinepubs/9699919799/functions/select.html
If you don't mind, I am going to close this problem report.
--
Totus tuus, Glebius.
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