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669ff911e2
Commit 27761a1042 ("Refactor atfork
handlers") introduced a lock, atfork_lock, around fork handler list
accesses. It turns out that this lock occasionally results in
self-deadlocks in malloc/tst-mallocfork2:
(gdb) bt
#0 __lll_lock_wait_private ()
at ../sysdeps/unix/sysv/linux/x86_64/lowlevellock.S:63
#1 0x00007f160c6f927a in __run_fork_handlers (who=(unknown: 209394016),
who@entry=atfork_run_prepare) at register-atfork.c:116
#2 0x00007f160c6b7897 in __libc_fork () at ../sysdeps/nptl/fork.c:58
#3 0x00000000004027d6 in sigusr1_handler (signo=<optimized out>)
at tst-mallocfork2.c:80
#4 sigusr1_handler (signo=<optimized out>) at tst-mallocfork2.c:64
#5 <signal handler called>
#6 0x00007f160c6f92e4 in __run_fork_handlers (who=who@entry=atfork_run_parent)
at register-atfork.c:136
#7 0x00007f160c6b79a2 in __libc_fork () at ../sysdeps/nptl/fork.c:152
#8 0x0000000000402567 in do_test () at tst-mallocfork2.c:156
#9 0x0000000000402dd2 in support_test_main (argc=1, argv=0x7ffc81ef1ab0,
config=config@entry=0x7ffc81ef1970) at support_test_main.c:350
#10 0x0000000000402362 in main (argc=<optimized out>, argv=<optimized out>)
at ../support/test-driver.c:168
If no locking happens in the single-threaded case (where fork is
expected to be async-signal-safe), this deadlock is avoided.
(pthread_atfork is not required to be async-signal-safe, so a fork
call from a signal handler interrupting pthread_atfork is not
a problem.)
67 lines
2.4 KiB
C
67 lines
2.4 KiB
C
/* Copyright (C) 2002-2019 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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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 <lowlevellock.h>
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/* The fork generation counter, defined in libpthread. */
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extern unsigned long int __fork_generation attribute_hidden;
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/* Pointer to the fork generation counter in the thread library. */
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extern unsigned long int *__fork_generation_pointer attribute_hidden;
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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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};
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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 handlers and lock/unlock the internal lock depending
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of the WHO argument:
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- atfork_run_prepare: run all the PREPARE_HANDLER in reverse order of
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insertion and locks the internal lock.
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- atfork_run_child: run all the CHILD_HANDLER and unlocks the internal
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lock.
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- atfork_run_parent: run all the PARENT_HANDLER and unlocks the internal
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lock.
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Perform locking only if DO_LOCKING. */
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extern void __run_fork_handlers (enum __run_fork_handler_type who,
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_Bool do_locking) 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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