Messages in this thread | | | Subject | RE: [Patch] Fix a race condition in pty.c | Date | Fri, 17 Dec 2004 09:09:15 -0800 | From | "Lu, Hongjiu" <> |
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Sorry I didn't mention that my testcase hang:
11540 pts/0 S 0:00 ./pty 11541 ? Zs 0:00 [true] <defunct>
Both parent and child are sleeping. They will never wake up. I updated my bug report
http://bugzilla.kernel.org/show_bug.cgi?id=3894
with the config file for P4 SMP machine.
H.J. Lu Intel Corporation
>-----Original Message----- >From: Andrew Morton [mailto:akpm@osdl.org] >Sent: Friday, December 17, 2004 12:36 AM >To: Zou, Nanhai >Cc: linux-kernel@vger.kernel.org; Lu, Hongjiu >Subject: Re: [Patch] Fix a race condition in pty.c > >"Zou, Nanhai" <nanhai.zou@intel.com> wrote: >> >> <<pty_close-race-fix.patch>> There is a race condition int pty.c >> when pty_close wakes up waiter on its pair device before set >> TTY_OTHER_CLOSED flag. >> >> It is possible on SMP or preempt kernel, waiter wakes up too early >that >> it will not get TTY_OTHER_CLOSED flag then fall into sleep again. >> >> Lu hong jiu report this bug will hang some expect scripts on SMP >> machines. > >The patch looks good (apart from the application/octet-stream encoding. >grr.) > >But on my test box it still doesn't fix the testcase which hj attached >to >bug 3894: > >select (3) returns: 1 >Read -1 characters. >errno: Input/output error >334 >select (3) returns: 1 >Read -1 characters. >errno: Input/output error >335 > >In fact the same happens on a non-preempt uniprocessor kernel, so I >must be >seeing something different. > >#include <sys/types.h> >#include <sys/select.h> >#include <stdio.h> >#include <unistd.h> >#include <pty.h> > >int >main () >{ > pid_t pid; > int fd; > char slave_name [20]; > char buffer [1000]; > int count; > fd_set readfds; > int ret; > > pid = forkpty (&fd, slave_name, NULL, NULL); > switch (pid) > { > case 0: /* Child process. */ > if (execlp ("true", "true", NULL)) > perror ("execlp"); > return 1; > break; > > default: /* Parent process. */ > break; > } > > FD_ZERO (&readfds); > FD_SET (fd, &readfds); > ret = select (1024, &readfds, NULL, NULL, NULL); > printf ("select (%d) returns: %d\n", fd, ret); > if (ret < 0) > perror ("select"); > else if (FD_ISSET (fd, &readfds)) > { > count = read (fd, buffer, 999); > printf ("Read %d characters.\n", count); > perror("errno"); > } > return 0; >}
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