posix: Fix system blocks SIGCHLD erroneously [BZ #30163]

Fix bug that SIGCHLD is erroneously blocked forever in the following
scenario:

1. Thread A calls system but hasn't returned yet
2. Thread B calls another system but returns

SIGCHLD would be blocked forever in thread B after its system() returns,
even after the system() in thread A returns.

Although POSIX does not require, glibc system implementation aims to be
thread and cancellation safe. This bug was introduced in
5fb7fc96350575c9adb1316833e48ca11553be49 when we moved reverting signal
mask to happen when the last concurrently running system returns,
despite that signal mask is per thread. This commit reverts this logic
and adds a test.

Signed-off-by: Adam Yi <ayi@janestreet.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>
(cherry picked from commit 436a604b7dc741fc76b5a6704c6cd8bb178518e7)

diff --git a/NEWS b/NEWS
index 9dd153477074904ceebefaece43423a727540ece..715316afe3628ecc5a13e04197f3252484545f0d 100644 (file)
--- a/NEWS
+++ b/NEWS
@@ -22,6 +22,7 @@ The following bugs are resolved with this release:
   [30125] dynamic-link: [regression, bisected] glibc-2.37 creates new
     symlink for libraries without soname
   [30151] gshadow: Matching sgetsgent, sgetsgent_r ERANGE handling
+  [30163] posix: Fix system blocks SIGCHLD erroneously
   [30305] x86_64: Fix asm constraints in feraiseexcept
 \f
 Version 2.37

diff --git a/stdlib/tst-system.c b/stdlib/tst-system.c
index 634acfe264136c72ecc2b6cf1d064295834940a8..47a0afe6bf2b118bf52c535f68d8eecc814e0ae5 100644 (file)
--- a/stdlib/tst-system.c
+++ b/stdlib/tst-system.c
@@ -25,6 +25,7 @@
 #include <support/check.h>
 #include <support/temp_file.h>
 #include <support/support.h>
+#include <support/xthread.h>
 #include <support/xunistd.h>
 
 static char *tmpdir;
@@ -71,6 +72,20 @@ call_system (void *closure)
     }
 }
 
+static void *
+sleep_and_check_sigchld (void *closure)
+{
+  double *seconds = (double *) closure;
+  char cmd[namemax];
+  sprintf (cmd, "sleep %lf" , *seconds);
+  TEST_COMPARE (system (cmd), 0);
+
+  sigset_t blocked = {0};
+  TEST_COMPARE (sigprocmask (SIG_BLOCK, NULL, &blocked), 0);
+  TEST_COMPARE (sigismember (&blocked, SIGCHLD), 0);
+  return NULL;
+}
+
 static int
 do_test (void)
 {
@@ -154,6 +169,17 @@ do_test (void)
     xchmod (_PATH_BSHELL, st.st_mode);
   }
 
+  {
+    pthread_t long_sleep_thread = xpthread_create (NULL,
+                                                   sleep_and_check_sigchld,
+                                                   &(double) { 0.2 });
+    pthread_t short_sleep_thread = xpthread_create (NULL,
+                                                    sleep_and_check_sigchld,
+                                                    &(double) { 0.1 });
+    xpthread_join (short_sleep_thread);
+    xpthread_join (long_sleep_thread);
+  }
+
   TEST_COMPARE (system (""), 0);
 
   return 0;

diff --git a/support/Makefile b/support/Makefile
index b29b7eb50578de1f93557fc6ad29471b54053586..48cd74581d548b8a0fefdbf445c8c9f3fbdcb8d7 100644 (file)
--- a/support/Makefile
+++ b/support/Makefile
@@ -32,6 +32,8 @@ libsupport-routines = \
   check_hostent \
   check_netent \
   delayed_exit \
+  dtotimespec \
+  dtotimespec-time64 \
   ignore_stderr \
   next_to_fault \
   oom_error \

diff --git a/support/dtotimespec-time64.c b/support/dtotimespec-time64.c
new file mode 100644 (file)
index 0000000..b3d5e35
--- /dev/null
+++ b/support/dtotimespec-time64.c
@@ -0,0 +1,27 @@
+/* Convert double to timespec.  64-bit time support.
+   Copyright (C) 2011-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library and is also part of gnulib.
+   Patches to this file should be submitted to both projects.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+#include <time.h>
+
+#if __TIMESIZE != 64
+# define timespec      __timespec64
+# define time_t        __time64_t
+# define dtotimespec   dtotimespec_time64
+# include "dtotimespec.c"
+#endif

diff --git a/support/dtotimespec.c b/support/dtotimespec.c
new file mode 100644 (file)
index 0000000..cde5b4d
--- /dev/null
+++ b/support/dtotimespec.c
@@ -0,0 +1,50 @@
+/* Convert double to timespec.
+   Copyright (C) 2011-2023 Free Software Foundation, Inc.
+   This file is part of the GNU C Library and is also part of gnulib.
+   Patches to this file should be submitted to both projects.
+
+   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
+   <https://www.gnu.org/licenses/>.  */
+
+/* Convert the double value SEC to a struct timespec.  Round toward
+   positive infinity.  On overflow, return an extremal value.  */
+
+#include <support/timespec.h>
+#include <intprops.h>
+
+struct timespec
+dtotimespec (double sec)
+{
+  if (sec <= TYPE_MINIMUM (time_t))
+    return make_timespec (TYPE_MINIMUM (time_t), 0);
+  else if (sec >= 1.0 + TYPE_MAXIMUM (time_t))
+    return make_timespec (TYPE_MAXIMUM (time_t), TIMESPEC_HZ - 1);
+  else
+    {
+      time_t s = sec;
+      double frac = TIMESPEC_HZ * (sec - s);
+      long ns = frac;
+      ns += ns < frac;
+      s += ns / TIMESPEC_HZ;
+      ns %= TIMESPEC_HZ;
+
+      if (ns < 0)
+        {
+          s--;
+          ns += TIMESPEC_HZ;
+        }
+
+      return make_timespec (s, ns);
+    }
+}

diff --git a/support/shell-container.c b/support/shell-container.c
index e9ac9b6d041b7a6e86376fce1c90d73c83fe9f65..66cf0c8b1f9274e36012e0ef2933a01316a5b745 100644 (file)
--- a/support/shell-container.c
+++ b/support/shell-container.c
@@ -39,6 +39,7 @@
 #include <error.h>
 
 #include <support/support.h>
+#include <support/timespec.h>
 
 /* Design considerations
 
@@ -171,6 +172,32 @@ kill_func (char **argv)
   return 0;
 }
 
+/* Emulate the "/bin/sleep" command.  No suffix support.  Options are
+   ignored.  */
+static int
+sleep_func (char **argv)
+{
+  if (argv[0] == NULL)
+    {
+      fprintf (stderr, "sleep: missing operand\n");
+      return 1;
+    }
+  char *endptr = NULL;
+  double sec = strtod (argv[0], &endptr);
+  if (endptr == argv[0] || errno == ERANGE || sec < 0)
+    {
+      fprintf (stderr, "sleep: invalid time interval '%s'\n", argv[0]);
+      return 1;
+    }
+  struct timespec ts = dtotimespec (sec);
+  if (nanosleep (&ts, NULL) < 0)
+    {
+      fprintf (stderr, "sleep: failed to nanosleep: %s\n", strerror (errno));
+      return 1;
+    }
+  return 0;
+}
+
 /* This is a list of all the built-in commands we understand.  */
 static struct {
   const char *name;
@@ -181,6 +208,7 @@ static struct {
   { "cp", copy_func },
   { "exit", exit_func },
   { "kill", kill_func },
+  { "sleep", sleep_func },
   { NULL, NULL }
 };
 

diff --git a/support/timespec.h b/support/timespec.h
index 77b1e4e8d676d466dda1dddcc99d707ea3ac35b6..9559836d4c7f7c3dc661c53b5218357c30c4a160 100644 (file)
--- a/support/timespec.h
+++ b/support/timespec.h
@@ -57,6 +57,8 @@ int support_timespec_check_in_range (struct timespec expected,
                                     struct timespec observed,
                                     double lower_bound, double upper_bound);
 
+struct timespec dtotimespec (double sec) __attribute__((const));
+
 #else
 struct timespec __REDIRECT (timespec_add, (struct timespec, struct timespec),
                            timespec_add_time64);
@@ -82,6 +84,8 @@ int __REDIRECT (support_timespec_check_in_range, (struct timespec expected,
                                                  double lower_bound,
                                                  double upper_bound),
                support_timespec_check_in_range_time64);
+
+struct timespec __REDIRECT (dtotimespec, (double sec), dtotimespec_time64);
 #endif
 
 /* Check that the timespec on the left represents a time before the

diff --git a/sysdeps/posix/system.c b/sysdeps/posix/system.c
index 2335a99184a2fc2f0d2975a145cf4dfd7dcfda2d..d77720a625e0d42a5cdca13961aae9db9c95ea78 100644 (file)
--- a/sysdeps/posix/system.c
+++ b/sysdeps/posix/system.c
@@ -179,16 +179,16 @@ do_system (const char *line)
       as if the shell had terminated using _exit(127).  */
    status = W_EXITCODE (127, 0);
 
+  /* sigaction can not fail with SIGINT/SIGQUIT used with old
+     disposition.  Same applies for sigprocmask.  */
   DO_LOCK ();
   if (SUB_REF () == 0)
     {
-      /* sigaction can not fail with SIGINT/SIGQUIT used with old
-        disposition.  Same applies for sigprocmask.  */
       __sigaction (SIGINT, &intr, NULL);
       __sigaction (SIGQUIT, &quit, NULL);
-      __sigprocmask (SIG_SETMASK, &omask, NULL);
     }
   DO_UNLOCK ();
+  __sigprocmask (SIG_SETMASK, &omask, NULL);
 
   if (ret != 0)
     __set_errno (ret);