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In multi-threaded programs, registering via pthread_atfork, de-registering implicitly via dlclose, or running pthread_atfork handlers during fork was protected by an internal lock. This meant that a pthread_atfork handler attempting to register another handler or dlclose a dynamically loaded library would lead to a deadlock. This commit fixes the deadlock in the following way: During the execution of handlers at fork time, the atfork lock is released prior to the execution of each handler and taken again upon its return. Any handler registrations or de-registrations that occurred during the execution of the handler are accounted for before proceeding with further handler execution. If a handler that hasn't been executed yet gets de-registered by another handler during fork, it will not be executed. If a handler gets registered by another handler during fork, it will not be executed during that particular fork. The possibility that handlers may now be registered or deregistered during handler execution means that identifying the next handler to be run after a given handler may register/de-register others requires some bookkeeping. The fork_handler struct has an additional field, 'id', which is assigned sequentially during registration. Thus, handlers are executed in ascending order of 'id' during 'prepare', and descending order of 'id' during parent/child handler execution after the fork. Two tests are included: * tst-atfork3: Adhemerval Zanella <adhemerval.zanella@linaro.org> This test exercises calling dlclose from prepare, parent, and child handlers. * tst-atfork4: This test exercises calling pthread_atfork and dlclose from the prepare handler. [BZ #24595, BZ #27054] Co-authored-by: Adhemerval Zanella <adhemerval.zanella@linaro.org> Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>
119 lines
3.1 KiB
C
119 lines
3.1 KiB
C
/* Check if pthread_atfork handler can call dlclose (BZ#24595).
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <stdio.h>
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#include <pthread.h>
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#include <unistd.h>
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#include <stdlib.h>
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#include <stdbool.h>
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#include <support/check.h>
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#include <support/xthread.h>
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#include <support/capture_subprocess.h>
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#include <support/xdlfcn.h>
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/* Check if pthread_atfork handlers do not deadlock when calling a function
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that might alter the internal fork handle list, such as dlclose.
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The test registers a callback set with pthread_atfork(), dlopen() a shared
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library (nptl/tst-atfork3mod.c), calls an exported symbol from the library
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(which in turn also registers atfork handlers), and calls fork to trigger
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the callbacks. */
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static void *handler;
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static bool run_dlclose_prepare;
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static bool run_dlclose_parent;
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static bool run_dlclose_child;
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static void
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prepare (void)
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{
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if (run_dlclose_prepare)
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xdlclose (handler);
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}
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static void
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parent (void)
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{
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if (run_dlclose_parent)
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xdlclose (handler);
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}
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static void
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child (void)
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{
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if (run_dlclose_child)
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xdlclose (handler);
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}
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static void
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proc_func (void *closure)
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{
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}
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static void
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do_test_generic (bool dlclose_prepare, bool dlclose_parent, bool dlclose_child)
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{
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run_dlclose_prepare = dlclose_prepare;
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run_dlclose_parent = dlclose_parent;
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run_dlclose_child = dlclose_child;
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handler = xdlopen ("tst-atfork3mod.so", RTLD_NOW);
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int (*atfork3mod_func)(void);
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atfork3mod_func = xdlsym (handler, "atfork3mod_func");
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atfork3mod_func ();
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struct support_capture_subprocess proc
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= support_capture_subprocess (proc_func, NULL);
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support_capture_subprocess_check (&proc, "tst-atfork3", 0, sc_allow_none);
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handler = atfork3mod_func = NULL;
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support_capture_subprocess_free (&proc);
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}
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static void *
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thread_func (void *closure)
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{
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return NULL;
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}
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static int
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do_test (void)
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{
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{
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/* Make the process acts as multithread. */
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pthread_attr_t attr;
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xpthread_attr_init (&attr);
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xpthread_attr_setdetachstate (&attr, PTHREAD_CREATE_DETACHED);
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xpthread_create (&attr, thread_func, NULL);
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}
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TEST_COMPARE (pthread_atfork (prepare, parent, child), 0);
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do_test_generic (true /* prepare */, false /* parent */, false /* child */);
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do_test_generic (false /* prepare */, true /* parent */, false /* child */);
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do_test_generic (false /* prepare */, false /* parent */, true /* child */);
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return 0;
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}
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#include <support/test-driver.c>
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