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

[fweimer at redhat dot com (Florian Weimer)]

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.

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;
 }