Messages in this thread Patch in this message | | | Date | Fri, 19 Jul 2002 02:52:04 -0700 (PDT) | From | Paul Eggert <> | Subject | [PATCH] 'select' failure or signal should not update timeout |
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[This follows up a thread in the emacs-pretesters mailing list about a problem with Emacs, 'select', SA_RESTART, and interrupts.]
> Date: Wed, 17 Jul 2002 08:30:57 -0600 (MDT) > From: Richard Stallman <rms@gnu.org> > > Is it true today that restarting a `select' call after a signal (with > SA_RESTART) alters the contents of the user's timeout parameter?
I looked into this a bit more, and it turns out to be a problem in the Linux kernel. POSIX 1003.1-2001 <http://www.opengroup.org/onlinepubs/007904975/functions/select.html> says that 'select' may modify its timeout argument only "upon successful completion". However, the Linux kernel sometimes modifies the timeout argument even when 'select' fails or is interrupted.
Here is a program that illustrates the problem. At the end of this message I enclose a proposed patch to the Linux kernel to fix the problem.
/* Conformance test for POSIX 1003.1-2001's requirement that select() must not update its timeout argument unless it succeeds. */
#include <signal.h> #include <stdio.h> #include <stdlib.h> #include <sys/time.h> #include <unistd.h>
static void moan (char const *string) { perror (string); exit (1); }
struct timeval timeout; struct timeval timeout_when_in_handler; struct sigaction act;
void handle_sigalrm (int sig) { timeout_when_in_handler = timeout; }
enum { TIMEOUT_SECONDS = 5 };
int main (int argc, char **argv) { act.sa_handler = handle_sigalrm; act.sa_flags = SA_RESTART; if (sigaction (SIGALRM, &act, 0) != 0) moan ("sigaction"); timeout.tv_sec = TIMEOUT_SECONDS; timeout_when_in_handler = timeout; alarm (TIMEOUT_SECONDS / 2); if (select (0, 0, 0, 0, &timeout) != 0) { if (timeout.tv_sec != TIMEOUT_SECONDS) { perror ("select"); fprintf (stderr, "select failed, but timeout was updated to %ld.%.9ld seconds\n", (long) timeout.tv_sec, timeout.tv_usec); } }
if (timeout_when_in_handler.tv_sec != TIMEOUT_SECONDS) fprintf (stderr, "timeout was updated to %ld.%.9ld seconds while signal handler was active\n", (long) timeout_when_in_handler.tv_sec, timeout_when_in_handler.tv_usec);
return 0; }
Here is a proposed patch to Linux kernel 2.5.26. The patch also applies to Linux 2.4.18, though you have to ignore the patches to files that do not exist in 2.4.18. I haven't tested this patch, but it's pretty straightforward.
diff -prU6 2.5.26/arch/ia64/ia32/sys_ia32.c 2.5.26-select/arch/ia64/ia32/sys_ia32.c --- 2.5.26/arch/ia64/ia32/sys_ia32.c Tue Jul 16 16:49:35 2002 +++ 2.5.26-select/arch/ia64/ia32/sys_ia32.c Fri Jul 19 02:17:08 2002 @@ -1058,32 +1058,32 @@ sys32_select (int n, fd_set *inp, fd_set zero_fd_set(n, fds.res_in); zero_fd_set(n, fds.res_out); zero_fd_set(n, fds.res_ex); ret = do_select(n, &fds, &timeout); + if (ret < 0) + goto out; + if (!ret) { + ret = -ERESTARTNOHAND; + if (signal_pending(current)) + goto out; + ret = 0; + } + if (tvp32 && !(current->personality & STICKY_TIMEOUTS)) { time_t sec = 0, usec = 0; if (timeout) { sec = timeout / HZ; usec = timeout % HZ; usec *= (1000000/HZ); } if (put_user(sec, &tvp32->tv_sec) || put_user(usec, &tvp32->tv_usec)) { ret = -EFAULT; goto out; } - } - - if (ret < 0) - goto out; - if (!ret) { - ret = -ERESTARTNOHAND; - if (signal_pending(current)) - goto out; - ret = 0; } set_fd_set(n, inp, fds.res_in); set_fd_set(n, outp, fds.res_out); set_fd_set(n, exp, fds.res_ex); diff -prU6 2.5.26/arch/mips64/kernel/linux32.c 2.5.26-select/arch/mips64/kernel/linux32.c --- 2.5.26/arch/mips64/kernel/linux32.c Tue Jul 16 16:49:25 2002 +++ 2.5.26-select/arch/mips64/kernel/linux32.c Fri Jul 19 02:18:19 2002 @@ -1170,30 +1170,30 @@ asmlinkage int sys32_select(int n, u32 * zero_fd_set(n, fds.res_in); zero_fd_set(n, fds.res_out); zero_fd_set(n, fds.res_ex); ret = do_select(n, &fds, &timeout); + if (ret < 0) + goto out; + if (!ret) { + ret = -ERESTARTNOHAND; + if (signal_pending(current)) + goto out; + ret = 0; + } + if (tvp && !(current->personality & STICKY_TIMEOUTS)) { time_t sec = 0, usec = 0; if (timeout) { sec = timeout / HZ; usec = timeout % HZ; usec *= (1000000/HZ); } put_user(sec, &tvp->tv_sec); put_user(usec, &tvp->tv_usec); - } - - if (ret < 0) - goto out; - if (!ret) { - ret = -ERESTARTNOHAND; - if (signal_pending(current)) - goto out; - ret = 0; } set_fd_set32(nn, inp, fds.res_in); set_fd_set32(nn, outp, fds.res_out); set_fd_set32(nn, exp, fds.res_ex); diff -prU6 2.5.26/arch/ppc64/kernel/sys_ppc32.c 2.5.26-select/arch/ppc64/kernel/sys_ppc32.c --- 2.5.26/arch/ppc64/kernel/sys_ppc32.c Tue Jul 16 16:49:36 2002 +++ 2.5.26-select/arch/ppc64/kernel/sys_ppc32.c Fri Jul 19 02:17:58 2002 @@ -762,30 +762,30 @@ asmlinkage long sys32_select(int n, u32 zero_fd_set(n, fds.res_in); zero_fd_set(n, fds.res_out); zero_fd_set(n, fds.res_ex); ret = do_select(n, &fds, &timeout); + if (ret < 0) + goto out; + if (!ret) { + ret = -ERESTARTNOHAND; + if (signal_pending(current)) + goto out; + ret = 0; + } + if (tvp && !(current->personality & STICKY_TIMEOUTS)) { time_t sec = 0, usec = 0; if (timeout) { sec = timeout / HZ; usec = timeout % HZ; usec *= (1000000/HZ); } put_user(sec, &tvp->tv_sec); put_user(usec, &tvp->tv_usec); - } - - if (ret < 0) - goto out; - if (!ret) { - ret = -ERESTARTNOHAND; - if (signal_pending(current)) - goto out; - ret = 0; } set_fd_set32(nn, inp, fds.res_in); set_fd_set32(nn, outp, fds.res_out); set_fd_set32(nn, exp, fds.res_ex); diff -prU6 2.5.26/arch/s390x/kernel/linux32.c 2.5.26-select/arch/s390x/kernel/linux32.c --- 2.5.26/arch/s390x/kernel/linux32.c Tue Jul 16 16:49:27 2002 +++ 2.5.26-select/arch/s390x/kernel/linux32.c Fri Jul 19 02:18:27 2002 @@ -1420,30 +1420,30 @@ asmlinkage int sys32_select(int n, u32 * zero_fd_set(n, fds.res_in); zero_fd_set(n, fds.res_out); zero_fd_set(n, fds.res_ex); ret = do_select(n, &fds, &timeout); + if (ret < 0) + goto out; + if (!ret) { + ret = -ERESTARTNOHAND; + if (signal_pending(current)) + goto out; + ret = 0; + } + if (tvp && !(current->personality & STICKY_TIMEOUTS)) { int sec = 0, usec = 0; if (timeout) { sec = timeout / HZ; usec = timeout % HZ; usec *= (1000000/HZ); } put_user(sec, &tvp->tv_sec); put_user(usec, &tvp->tv_usec); - } - - if (ret < 0) - goto out; - if (!ret) { - ret = -ERESTARTNOHAND; - if (signal_pending(current)) - goto out; - ret = 0; } set_fd_set32(nn, inp, fds.res_in); set_fd_set32(nn, outp, fds.res_out); set_fd_set32(nn, exp, fds.res_ex); diff -prU6 2.5.26/arch/sparc64/kernel/sys_sparc32.c 2.5.26-select/arch/sparc64/kernel/sys_sparc32.c --- 2.5.26/arch/sparc64/kernel/sys_sparc32.c Tue Jul 16 16:49:35 2002 +++ 2.5.26-select/arch/sparc64/kernel/sys_sparc32.c Fri Jul 19 02:16:59 2002 @@ -1387,30 +1387,30 @@ asmlinkage int sys32_select(int n, u32 * zero_fd_set(n, fds.res_in); zero_fd_set(n, fds.res_out); zero_fd_set(n, fds.res_ex); ret = do_select(n, &fds, &timeout); + if (ret < 0) + goto out; + if (!ret) { + ret = -ERESTARTNOHAND; + if (signal_pending(current)) + goto out; + ret = 0; + } + if (tvp && !(current->personality & STICKY_TIMEOUTS)) { time_t sec = 0, usec = 0; if (timeout) { sec = timeout / HZ; usec = timeout % HZ; usec *= (1000000/HZ); } put_user(sec, &tvp->tv_sec); put_user(usec, &tvp->tv_usec); - } - - if (ret < 0) - goto out; - if (!ret) { - ret = -ERESTARTNOHAND; - if (signal_pending(current)) - goto out; - ret = 0; } set_fd_set32(nn, inp, fds.res_in); set_fd_set32(nn, outp, fds.res_out); set_fd_set32(nn, exp, fds.res_ex); diff -prU6 2.5.26/arch/x86_64/ia32/sys_ia32.c 2.5.26-select/arch/x86_64/ia32/sys_ia32.c --- 2.5.26/arch/x86_64/ia32/sys_ia32.c Tue Jul 16 16:49:32 2002 +++ 2.5.26-select/arch/x86_64/ia32/sys_ia32.c Fri Jul 19 02:18:07 2002 @@ -878,30 +878,30 @@ sys32_select(int n, fd_set *inp, fd_set zero_fd_set(n, fds.res_in); zero_fd_set(n, fds.res_out); zero_fd_set(n, fds.res_ex); ret = do_select(n, &fds, &timeout); + if (ret < 0) + goto out; + if (!ret) { + ret = -ERESTARTNOHAND; + if (signal_pending(current)) + goto out; + ret = 0; + } + if (tvp32 && !(current->personality & STICKY_TIMEOUTS)) { time_t sec = 0, usec = 0; if (timeout) { sec = timeout / HZ; usec = timeout % HZ; usec *= (1000000/HZ); } put_user(sec, (int *)&tvp32->tv_sec); put_user(usec, (int *)&tvp32->tv_usec); - } - - if (ret < 0) - goto out; - if (!ret) { - ret = -ERESTARTNOHAND; - if (signal_pending(current)) - goto out; - ret = 0; } set_fd_set(n, inp, fds.res_in); set_fd_set(n, outp, fds.res_out); set_fd_set(n, exp, fds.res_ex); diff -prU6 2.5.26/fs/select.c 2.5.26-select/fs/select.c --- 2.5.26/fs/select.c Tue Jul 16 16:49:24 2002 +++ 2.5.26-select/fs/select.c Fri Jul 19 02:18:41 2002 @@ -316,30 +316,30 @@ sys_select(int n, fd_set *inp, fd_set *o zero_fd_set(n, fds.res_in); zero_fd_set(n, fds.res_out); zero_fd_set(n, fds.res_ex); ret = do_select(n, &fds, &timeout); + if (ret < 0) + goto out; + if (!ret) { + ret = -ERESTARTNOHAND; + if (signal_pending(current)) + goto out; + ret = 0; + } + if (tvp && !(current->personality & STICKY_TIMEOUTS)) { time_t sec = 0, usec = 0; if (timeout) { sec = timeout / HZ; usec = timeout % HZ; usec *= (1000000/HZ); } put_user(sec, &tvp->tv_sec); put_user(usec, &tvp->tv_usec); - } - - if (ret < 0) - goto out; - if (!ret) { - ret = -ERESTARTNOHAND; - if (signal_pending(current)) - goto out; - ret = 0; } set_fd_set(n, inp, fds.res_in); set_fd_set(n, outp, fds.res_out); set_fd_set(n, exp, fds.res_ex); - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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