52a103e237
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>
64 lines
2.3 KiB
C
64 lines
2.3 KiB
C
/* Internal pthread_atfork definitions.
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Copyright (C) 2021-2022 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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<https://www.gnu.org/licenses/>. */
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#ifndef _REGISTER_ATFORK_H
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#define _REGISTER_ATFORK_H
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/* Elements of the fork handler lists. */
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struct fork_handler
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{
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void (*prepare_handler) (void);
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void (*parent_handler) (void);
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void (*child_handler) (void);
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void *dso_handle;
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uint64_t id;
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};
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/* Function to call to unregister fork handlers. */
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extern void __unregister_atfork (void *dso_handle) attribute_hidden;
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#define UNREGISTER_ATFORK(dso_handle) __unregister_atfork (dso_handle)
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enum __run_fork_handler_type
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{
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atfork_run_prepare,
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atfork_run_child,
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atfork_run_parent
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};
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/* Run the atfork prepare handlers in the reverse order of registration and
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return the ID of the last registered handler. If DO_LOCKING is true, the
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internal lock is held locked upon return. */
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extern uint64_t __run_prefork_handlers (_Bool do_locking) attribute_hidden;
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/* Given a handler type (parent or child), run all the atfork handlers in
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the order of registration up to and including the handler with id equal
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to LASTRUN. If DO_LOCKING is true, the internal lock is unlocked prior
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to return. */
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extern void __run_postfork_handlers (enum __run_fork_handler_type who,
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_Bool do_locking,
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uint64_t lastrun) attribute_hidden;
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/* C library side function to register new fork handlers. */
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extern int __register_atfork (void (*__prepare) (void),
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void (*__parent) (void),
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void (*__child) (void),
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void *dso_handle);
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libc_hidden_proto (__register_atfork)
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#endif
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