[patch] Fix dlclose / exit running in parallel resulting in dtor being called twice
Paul Pluzhnikov
ppluzhnikov@google.com
Wed Sep 20 18:31:00 GMT 2017
Greetings,
This a followup to and fix for the problem discovered in
https://sourceware.org/ml/libc-alpha/2017-09/msg00762.html.
As the test program in above message shows, dlclose running in
parallel with exit currently results in "second" being called twice.
The fix for this is trivial (2 line change in stdlib/exit.c). The
majority of this patch is the test case, which is modified from
original to avoid sleep.
Thanks,
P.S. Not sure what commit message should be for this patch.
--
Paul Pluzhnikov
-------------- next part --------------
2017-09-20 Paul Pluzhnikov <ppluzhnikov@google.com>
Carlos O'Donell <carlos@redhat.com>
* stdlib/Makefile (tests): Add test-dlclose-exit-race.
* stdlib/test-dlclose-exit-race.c: New file.
* stdlib/test-dlclose-exit-race-helper.c: New file.
* stdlib/exit.c (__run_exit_handlers): Mark slot as free.
diff --git a/stdlib/Makefile b/stdlib/Makefile
index 2fb08342e0..443230bbb7 100644
--- a/stdlib/Makefile
+++ b/stdlib/Makefile
@@ -83,7 +83,7 @@ tests := tst-strtol tst-strtod testmb testrand testsort testdiv \
tst-getrandom tst-atexit tst-at_quick_exit \
tst-cxa_atexit tst-on_exit test-atexit-race \
test-at_quick_exit-race test-cxa_atexit-race \
- test-on_exit-race
+ test-on_exit-race test-dlclose-exit-race
tests-internal := tst-strtod1i tst-strtod3 tst-strtod4 tst-strtod5i \
tst-tls-atexit tst-tls-atexit-nodelete
@@ -98,6 +98,10 @@ LDLIBS-test-at_quick_exit-race = $(shared-thread-library)
LDLIBS-test-cxa_atexit-race = $(shared-thread-library)
LDLIBS-test-on_exit-race = $(shared-thread-library)
+LDLIBS-test-dlclose-exit-race = $(libsupport) $(shared-thread-library) $(libdl)
+LDFLAGS-test-dlclose-exit-race = $(LDFLAGS-rdynamic)
+LDLIBS-test-dlclose-exit-race-helper.so = $(libsupport) $(shared-thread-library)
+
ifeq ($(have-cxx-thread_local),yes)
CFLAGS-tst-quick_exit.o = -std=c++11
LDLIBS-tst-quick_exit = -lstdc++
@@ -108,7 +112,7 @@ else
tests-unsupported += tst-quick_exit tst-thread-quick_exit
endif
-modules-names = tst-tls-atexit-lib
+modules-names = tst-tls-atexit-lib test-dlclose-exit-race-helper
extra-test-objs += $(addsuffix .os, $(modules-names))
ifeq ($(build-shared),yes)
@@ -177,6 +181,7 @@ $(objpfx)tst-strtod-nan-locale.out: $(gen-locales)
$(objpfx)tst-strfmon_l.out: $(gen-locales)
$(objpfx)tst-strfrom.out: $(gen-locales)
$(objpfx)tst-strfrom-locale.out: $(gen-locales)
+$(objpfx)test-dlclose-exit-race.out: $(objpfx)test-dlclose-exit-race-helper.so
endif
# Testdir has to be named stdlib and needs to be writable
@@ -215,6 +220,7 @@ $(objpfx)tst-strtod6: $(libm)
$(objpfx)tst-strtod-nan-locale: $(libm)
tst-tls-atexit-lib.so-no-z-defs = yes
+test-dlclose-exit-race-helper.so-no-z-defs = yes
$(objpfx)tst-tls-atexit: $(shared-thread-library) $(libdl)
$(objpfx)tst-tls-atexit.out: $(objpfx)tst-tls-atexit-lib.so
diff --git a/stdlib/exit.c b/stdlib/exit.c
index b74f1825f0..6a354fd0af 100644
--- a/stdlib/exit.c
+++ b/stdlib/exit.c
@@ -69,8 +69,7 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
while (cur->idx > 0)
{
- const struct exit_function *const f =
- &cur->fns[--cur->idx];
+ struct exit_function *const f = &cur->fns[--cur->idx];
const uint64_t new_exitfn_called = __new_exitfn_called;
/* Unlock the list while we call a foreign function. */
@@ -99,6 +98,9 @@ __run_exit_handlers (int status, struct exit_function_list **listp,
atfct ();
break;
case ef_cxa:
+ /* To avoid dlopen/exit race calling cxafct twice, we must
+ mark this function as ef_free. */
+ f->flavor = ef_free;
cxafct = f->func.cxa.fn;
#ifdef PTR_DEMANGLE
PTR_DEMANGLE (cxafct);
diff --git a/stdlib/test-dlclose-exit-race-helper.c b/stdlib/test-dlclose-exit-race-helper.c
new file mode 100644
index 0000000000..1b443e0b52
--- /dev/null
+++ b/stdlib/test-dlclose-exit-race-helper.c
@@ -0,0 +1,80 @@
+/* Helper for exit/dlclose race test.
+ 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 <stdio.h>
+#include <stdbool.h>
+#include <stdlib.h>
+#include <semaphore.h>
+#include <unistd.h>
+#include <support/xthread.h>
+
+/* Semaphore defined in executable to ensure we have a happens-before
+ between the first function starting and exit being called. */
+extern sem_t order1;
+
+/* Semaphore defined in executable to ensure we have a happens-before
+ between the second function starting and the first function returning. */
+extern sem_t order2;
+
+/* glibc function for registering DSO-specific exit functions. */
+extern int __cxa_atexit (void (*func) (void *), void *arg, void *dso_handle);
+
+/* Hidden compiler handle to this shared object. */
+extern void *__dso_handle __attribute__ ((__weak__));
+
+static void
+first (void *start)
+{
+ /* Let the exiting thread run. */
+ sem_post (&order1);
+
+ /* Wait for exiting thread to finish. */
+ sem_wait (&order2);
+
+ printf ("first\n");
+}
+
+static void
+second (void *start)
+{
+ /* We may be called from different threads.
+ This lock protects called. */
+ static pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
+ static bool called = false;
+
+ xpthread_mutex_lock (&mtx);
+ if (called)
+ {
+ fprintf (stderr, "second called twice!\n");
+ abort ();
+ }
+ called = true;
+ xpthread_mutex_unlock (&mtx);
+
+ printf ("second\n");
+}
+
+
+__attribute__ ((constructor)) static void
+constructor (void)
+{
+ sem_init (&order1, 0, 0);
+ sem_init (&order2, 0, 0);
+ __cxa_atexit (second, NULL, __dso_handle);
+ __cxa_atexit (first, NULL, __dso_handle);
+}
diff --git a/stdlib/test-dlclose-exit-race.c b/stdlib/test-dlclose-exit-race.c
new file mode 100644
index 0000000000..bbb97c7c64
--- /dev/null
+++ b/stdlib/test-dlclose-exit-race.c
@@ -0,0 +1,116 @@
+/* Test for exit/dlclose race.
+ 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/>. */
+
+/* This file must be run from within a directory called "stdlib". */
+
+/* This test verifies that when dlopen in one thread races against exit
+ in another thread, we don't call registered destructor twice.
+
+ Expected result:
+ second
+ first
+ ... clean termination
+*/
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <dlfcn.h>
+#include <semaphore.h>
+#include <support/xthread.h>
+
+/* Semaphore to ensure we have a happens-before between the first function
+ starting and exit being called. */
+sem_t order1;
+
+/* Semaphore to ensure we have a happens-before between the second function
+ starting and the first function returning. */
+sem_t order2;
+
+void *
+open_library (const char * pathname)
+{
+ void *dso;
+ char *err;
+
+ /* Open the DSO. */
+ dso = dlopen (pathname, RTLD_NOW|RTLD_GLOBAL);
+ if (dso == NULL)
+ {
+ err = dlerror ();
+ fprintf (stderr, "%s\n", err);
+ exit (1);
+ }
+ /* Clear any errors. */
+ dlerror ();
+ return dso;
+}
+
+int
+close_library (void *dso)
+{
+ int ret;
+ char *err;
+
+ /* Close the library and look for errors too. */
+ ret = dlclose (dso);
+ if (ret != 0)
+ {
+ err = dlerror ();
+ fprintf (stderr, "%s\n", err);
+ exit (1);
+ }
+ return ret;
+}
+
+void *
+exit_thread (void *arg)
+{
+ /* Wait for the dlclose to start... */
+ sem_wait (&order1);
+ /* Then try to run the exit sequence which should call all
+ __cxa_atexit registered functions and in parallel with
+ the executing dlclose(). */
+ exit (0);
+}
+
+
+void
+last (void)
+{
+ /* Let dlclose thread proceed. */
+ sem_post (&order2);
+}
+
+int
+main (void)
+{
+ void *dso;
+ pthread_t thread;
+
+ atexit (last);
+
+ dso = open_library ("$ORIGIN/test-dlclose-exit-race-helper.so");
+ thread = xpthread_create (NULL, exit_thread, NULL);
+
+ close_library (dso);
+ xpthread_join (thread);
+
+ /* Unreached. */
+ fprintf (stderr, "Reached unreachable code.");
+ abort ();
+}
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