Re: [PATCH] sigwait: Do not fail with EINTR and return error code [BZ #22478]

[Adhemerval Zanella <adhemerval dot zanella at linaro dot org>]

On 22/11/2017 18:15, Florian Weimer wrote:
> Since
> 
> commit 8b0e795aaa445e9167aa07b282c5720b35342c07
> Author: Adhemerval Zanella <adhemerval.zanella@linaro.org>
> Date:   Wed Nov 1 11:49:05 2017 -0200
> 
>     Simplify Linux sig{timed}wait{info} implementations
> 
> sigwait can fail with EINTR.  Applications do not expect that, and the
> error code is not documented in POSIX or the manual pages.
> 
> This commit restores the previous behavior by retrying the system call
> on EINTR.  It also returns the error code, not -1, on the remaing
> errors.
> 
> 2017-11-22  Florian Weimer  <fweimer@redhat.com>
> 
> 	[BZ #22478]
> 	* sysdeps/unix/sysv/linux/sigwait.c (__sigwait): Retry on EINTR.
> 	Return error code, not -1.
> 	* signal/tst-sigwait-eintr.c: New file.
> 	* signal/Makefile (tests): Add tst-sigwait-eintr.

Thanks for catching it.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>

> 
> diff --git a/signal/Makefile b/signal/Makefile
> index a6a1289437..c2dc719d70 100644
> --- a/signal/Makefile
> +++ b/signal/Makefile
> @@ -45,8 +45,8 @@ routines	:= signal raise killpg \
>  		   allocrtsig sigtimedwait sigwaitinfo sigqueue \
>  		   sighold sigrelse sigignore sigset
>  
> -tests		:= tst-signal tst-sigset tst-sigsimple tst-raise tst-sigset2
> -
> +tests		:= tst-signal tst-sigset tst-sigsimple tst-raise tst-sigset2 \
> +  tst-sigwait-eintr \
>  
>  include ../Rules
>  
> diff --git a/signal/tst-sigwait-eintr.c b/signal/tst-sigwait-eintr.c
> new file mode 100644
> index 0000000000..7149eb93c3
> --- /dev/null
> +++ b/signal/tst-sigwait-eintr.c
> @@ -0,0 +1,85 @@
> +/* Check that sigwait does not fail with EINTR (bug 22478).
> +   Copyright (C) 2017 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <http://www.gnu.org/licenses/>.  */
> +
> +#include <errno.h>
> +#include <signal.h>
> +#include <stdio.h>
> +#include <support/check.h>
> +#include <support/xunistd.h>
> +#include <time.h>
> +#include <unistd.h>
> +
> +/* Handler for SIGUSR1.  */
> +static void
> +sigusr1_handler (int signo)
> +{
> +  TEST_VERIFY (signo == SIGUSR1);
> +}
> +
> +/* Spawn a subprocess to send two signals: First SIGUSR1, then
> +   SIGUSR2.  Return the PID of the process.  */
> +static pid_t
> +signal_sender (void)
> +{
> +  pid_t pid = xfork ();
> +  if (pid == 0)
> +    {
> +      static const struct timespec delay = { 1, };
> +      if (nanosleep (&delay, NULL) != 0)
> +        FAIL_EXIT1 ("nanosleep: %m");
> +      if (kill (getppid (), SIGUSR1) != 0)
> +        FAIL_EXIT1 ("kill (SIGUSR1): %m");
> +      if (nanosleep (&delay, NULL) != 0)
> +        FAIL_EXIT1 ("nanosleep: %m");
> +      if (kill (getppid (), SIGUSR2) != 0)
> +        FAIL_EXIT1 ("kill (SIGUSR2): %m");
> +      _exit (0);
> +    }
> +  return pid;
> +}
> +
> +static int
> +do_test (void)
> +{
> +  if (signal (SIGUSR1, sigusr1_handler) == SIG_ERR)
> +    FAIL_EXIT1 ("signal (SIGUSR1): %m\n");
> +
> +  sigset_t sigs;
> +  sigemptyset (&sigs);
> +  sigaddset (&sigs, SIGUSR2);
> +  if (sigprocmask (SIG_BLOCK, &sigs, NULL) != 0)
> +    FAIL_EXIT1 ("sigprocmask (SIGBLOCK, SIGUSR2): %m");
> +  pid_t pid = signal_sender ();
> +  int signo = 0;
> +  int ret = sigwait (&sigs, &signo);
> +  if (ret != 0)
> +    {
> +      support_record_failure ();
> +      errno = ret;
> +      printf ("error: sigwait failed: %m (%d)\n", ret);
> +    }
> +  TEST_VERIFY (signo == SIGUSR2);
> +
> +  int status;
> +  xwaitpid (pid, &status, 0);
> +  TEST_VERIFY (status == 0);
> +
> +  return 0;
> +}
> +
> +#include <support/test-driver.c>
> diff --git a/sysdeps/unix/sysv/linux/sigwait.c b/sysdeps/unix/sysv/linux/sigwait.c
> index e6fb32a610..443c3ad8e1 100644
> --- a/sysdeps/unix/sysv/linux/sigwait.c
> +++ b/sysdeps/unix/sysv/linux/sigwait.c
> @@ -17,13 +17,20 @@
>  
>  #include <signal.h>
>  #include <sysdep-cancel.h>
> +#include <errno.h>
>  
>  int
>  __sigwait (const sigset_t *set, int *sig)
>  {
>    siginfo_t si;
> -  if (__sigtimedwait (set, &si, 0) < 0)
> -    return -1;
> +  int ret;
> +  do
> +    ret = __sigtimedwait (set, &si, 0);
> +  /* Applications do not expect sigwait to return with EINTR, and the
> +     error code is not specified by POSIX.  */
> +  while (ret < 0 && errno == EINTR);
> +  if (ret < 0)
> +    return errno;
>    *sig = si.si_signo;
>    return 0;
>  }
>