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authorAdhemerval Zanella <adhemerval.zanella@linaro.org>2021-01-19 09:26:31 -0300
committerAdhemerval Zanella <adhemerval.zanella@linaro.org>2021-06-28 15:55:56 -0300
commitc32c868ab8b2b95724550d0130782c0767fc3bab (patch)
tree53b43a7f006fe8f549affb6b6d4d24b808a75465 /posix
parentdd45734e322a03287d34d8af9b7da7b35cfddb8e (diff)
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posix: Add _Fork [BZ #4737]
Austin Group issue 62 [1] dropped the async-signal-safe requirement for fork and provided a async-signal-safe _Fork replacement that does not run the atfork handlers. It will be included in the next POSIX standard. It allow to close a long standing issue to make fork AS-safe (BZ#4737). As indicated on the bug, besides the internal lock for the atfork handlers itself; there is no guarantee that the handlers itself will not introduce more AS-safe issues. The idea is synchronize fork with the required internal locks to allow children in multithread processes to use mostly of standard function (even though POSIX states only AS-safe function should be used). On signal handles, _Fork should be used intead and only AS-safe functions should be used. For testing, the new tst-_Fork only check basic usage. I also added a new tst-mallocfork3 which uses the same strategy to check for deadlock of tst-mallocfork2 but using threads instead of subprocesses (and it does deadlock if it replaces _Fork with fork). [1] https://austingroupbugs.net/view.php?id=62
Diffstat (limited to 'posix')
-rw-r--r--posix/Makefile3
-rw-r--r--posix/Versions1
-rw-r--r--posix/fork.c5
-rw-r--r--posix/tst-_Fork.c154
-rw-r--r--posix/unistd.h7
5 files changed, 168 insertions, 2 deletions
diff --git a/posix/Makefile b/posix/Makefile
index 3bd7d605df..e91ea25ba1 100644
--- a/posix/Makefile
+++ b/posix/Makefile
@@ -130,7 +130,7 @@ test-srcs := globtest
tests += wordexp-test tst-exec tst-spawn tst-spawn2 tst-spawn3
endif
ifeq (yesyes,$(build-shared)$(have-thread-library))
-tests += tst-getopt-cancel
+tests += tst-getopt-cancel tst-_Fork
endif
tests-static = tst-exec-static tst-spawn-static
tests += $(tests-static)
@@ -299,6 +299,7 @@ $(objpfx)ptestcases.h: PTESTS PTESTS2C.sed
$(objpfx)runptests.o: $(objpfx)ptestcases.h
$(objpfx)tst-getopt-cancel: $(shared-thread-library)
+$(objpfx)tst-_Fork: $(shared-thread-library)
test-xfail-annexc = yes
$(objpfx)annexc.out: $(objpfx)annexc
diff --git a/posix/Versions b/posix/Versions
index 5983144d01..ee1f412185 100644
--- a/posix/Versions
+++ b/posix/Versions
@@ -152,6 +152,7 @@ libc {
GLIBC_2.30 {
}
GLIBC_2.34 {
+ _Fork;
execveat;
}
GLIBC_PRIVATE {
diff --git a/posix/fork.c b/posix/fork.c
index 940d6a0955..c471f7b15f 100644
--- a/posix/fork.c
+++ b/posix/fork.c
@@ -41,7 +41,10 @@ __libc_fork (void)
{
/* Determine if we are running multiple threads. We skip some fork
handlers in the single-thread case, to make fork safer to use in
- signal handlers. */
+ signal handlers. Although POSIX has dropped async-signal-safe
+ requirement for fork (Austin Group tracker issue #62) this is
+ best effort to make is async-signal-safe at least for single-thread
+ case. */
bool multiple_threads = __libc_single_threaded == 0;
__run_fork_handlers (atfork_run_prepare, multiple_threads);
diff --git a/posix/tst-_Fork.c b/posix/tst-_Fork.c
new file mode 100644
index 0000000000..43a65c0fea
--- /dev/null
+++ b/posix/tst-_Fork.c
@@ -0,0 +1,154 @@
+/* Basic tests for _Fork.
+ Copyright (C) 2021 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
+ <https://www.gnu.org/licenses/>. */
+
+#include <array_length.h>
+#include <stdlib.h>
+#include <string.h>
+#include <pthread.h>
+#include <stdbool.h>
+#include <support/check.h>
+#include <support/xsignal.h>
+#include <support/temp_file.h>
+#include <support/xunistd.h>
+#include <support/xthread.h>
+
+/* For single-thread, _Fork behaves like fork. */
+static int
+singlethread_test (void)
+{
+ const char testdata1[] = "abcdefghijklmnopqrtuvwxz";
+ enum { testdatalen1 = array_length (testdata1) };
+ const char testdata2[] = "01234567890";
+ enum { testdatalen2 = array_length (testdata2) };
+
+ pid_t ppid = getpid ();
+
+ int tempfd = create_temp_file ("tst-_Fork", NULL);
+
+ /* Check if the opened file is shared between process by read and write
+ some data on parent and child processes. */
+ xwrite (tempfd, testdata1, testdatalen1);
+ off_t off = xlseek (tempfd, 0, SEEK_CUR);
+ TEST_COMPARE (off, testdatalen1);
+
+ pid_t pid = _Fork ();
+ TEST_VERIFY_EXIT (pid != -1);
+ if (pid == 0)
+ {
+ TEST_VERIFY_EXIT (getpid () != ppid);
+ TEST_COMPARE (getppid(), ppid);
+
+ TEST_COMPARE (xlseek (tempfd, 0, SEEK_CUR), testdatalen1);
+
+ xlseek (tempfd, 0, SEEK_SET);
+ char buf[testdatalen1];
+ TEST_COMPARE (read (tempfd, buf, sizeof (buf)), testdatalen1);
+ TEST_COMPARE_BLOB (buf, testdatalen1, testdata1, testdatalen1);
+
+ xlseek (tempfd, 0, SEEK_SET);
+ xwrite (tempfd, testdata2, testdatalen2);
+
+ xclose (tempfd);
+
+ _exit (EXIT_SUCCESS);
+ }
+
+ int status;
+ xwaitpid (pid, &status, 0);
+ TEST_VERIFY (WIFEXITED (status));
+ TEST_COMPARE (WEXITSTATUS (status), EXIT_SUCCESS);
+
+ TEST_COMPARE (xlseek (tempfd, 0, SEEK_CUR), testdatalen2);
+
+ xlseek (tempfd, 0, SEEK_SET);
+ char buf[testdatalen2];
+ TEST_COMPARE (read (tempfd, buf, sizeof (buf)), testdatalen2);
+
+ TEST_COMPARE_BLOB (buf, testdatalen2, testdata2, testdatalen2);
+
+ return 0;
+}
+
+
+static volatile sig_atomic_t sigusr1_handler_ran;
+#define SIG_PID_EXIT_CODE 20
+
+static bool atfork_prepare_var;
+static bool atfork_parent_var;
+static bool atfork_child_var;
+
+static void
+atfork_prepare (void)
+{
+ atfork_prepare_var = true;
+}
+
+static void
+atfork_parent (void)
+{
+ atfork_parent_var = true;
+}
+
+static void
+atfork_child (void)
+{
+ atfork_child_var = true;
+}
+
+/* Different than fork, _Fork does not execute any pthread_atfork
+ handlers. */
+static int
+singlethread_atfork_test (void)
+{
+ pthread_atfork (atfork_prepare, atfork_parent, atfork_child);
+ singlethread_test ();
+ TEST_VERIFY (!atfork_prepare_var);
+ TEST_VERIFY (!atfork_parent_var);
+ TEST_VERIFY (!atfork_child_var);
+
+ return 0;
+}
+
+static void *
+mt_atfork_test (void *args)
+{
+ singlethread_atfork_test ();
+
+ return NULL;
+}
+
+static int
+multithread_atfork_test (void)
+{
+ pthread_t thr = xpthread_create (NULL, mt_atfork_test, NULL);
+ xpthread_join (thr);
+
+ return 0;
+}
+
+
+static int
+do_test (void)
+{
+ singlethread_atfork_test ();
+ multithread_atfork_test ();
+
+ return 0;
+}
+
+#include <support/test-driver.c>
diff --git a/posix/unistd.h b/posix/unistd.h
index d9d8929f71..217c6c5363 100644
--- a/posix/unistd.h
+++ b/posix/unistd.h
@@ -781,6 +781,13 @@ extern __pid_t fork (void) __THROWNL;
extern __pid_t vfork (void) __THROW;
#endif /* Use misc or XPG < 7. */
+#ifdef __USE_GNU
+/* This is similar to fork, however it does not run the atfork handlers
+ neither reinitialize any internal locks in multithread case.
+ Different than fork, _Fork is async-signal-safe. */
+extern __pid_t _Fork (void) __THROW;
+#endif
+
/* Return the pathname of the terminal FD is open on, or NULL on errors.
The returned storage is good only until the next call to this function. */