389fdf78b2
POSIX and C++11 require that a thread can destroy a mutex if no other thread owns the mutex, is blocked on the mutex, or will try to acquire it in the future. After destroying the mutex, it can reuse or unmap the underlying memory. Thus, we must not access a mutex' memory after releasing it. Currently, we can load the private flag after releasing the mutex, which is fixed by this patch. See https://sourceware.org/bugzilla/show_bug.cgi?id=13690 for more background. We need to call futex_wake on the lock after releasing it, however. This is by design, and can lead to spurious wake-ups on unrelated futex words (e.g., when the mutex memory is reused for another mutex). This behavior is documented in the glibc-internal futex API and in recent drafts of the Linux kernel's futex documentation (see the draft_futex branch of git://git.kernel.org/pub/scm/docs/man-pages/man-pages.git).
146 lines
5.6 KiB
C
146 lines
5.6 KiB
C
/* Low-level locking access to futex facilities. Linux version.
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Copyright (C) 2005-2015 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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#ifndef _LOWLEVELLOCK_FUTEX_H
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#define _LOWLEVELLOCK_FUTEX_H 1
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#ifndef __ASSEMBLER__
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#include <sysdep.h>
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#include <tls.h>
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#include <kernel-features.h>
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#endif
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#define FUTEX_WAIT 0
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#define FUTEX_WAKE 1
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#define FUTEX_REQUEUE 3
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#define FUTEX_CMP_REQUEUE 4
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#define FUTEX_WAKE_OP 5
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#define FUTEX_OP_CLEAR_WAKE_IF_GT_ONE ((4 << 24) | 1)
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#define FUTEX_LOCK_PI 6
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#define FUTEX_UNLOCK_PI 7
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#define FUTEX_TRYLOCK_PI 8
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#define FUTEX_WAIT_BITSET 9
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#define FUTEX_WAKE_BITSET 10
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#define FUTEX_WAIT_REQUEUE_PI 11
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#define FUTEX_CMP_REQUEUE_PI 12
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#define FUTEX_PRIVATE_FLAG 128
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#define FUTEX_CLOCK_REALTIME 256
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#define FUTEX_BITSET_MATCH_ANY 0xffffffff
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/* Values for 'private' parameter of locking macros. Yes, the
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definition seems to be backwards. But it is not. The bit will be
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reversed before passing to the system call. */
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#define LLL_PRIVATE 0
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#define LLL_SHARED FUTEX_PRIVATE_FLAG
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#ifndef __ASSEMBLER__
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#if IS_IN (libc) || IS_IN (rtld)
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/* In libc.so or ld.so all futexes are private. */
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# ifdef __ASSUME_PRIVATE_FUTEX
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# define __lll_private_flag(fl, private) \
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({ \
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/* Prevent warnings in callers of this macro. */ \
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int __lll_private_flag_priv __attribute__ ((unused)); \
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__lll_private_flag_priv = (private); \
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((fl) | FUTEX_PRIVATE_FLAG); \
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})
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# else
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# define __lll_private_flag(fl, private) \
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((fl) | THREAD_GETMEM (THREAD_SELF, header.private_futex))
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# endif
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#else
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# ifdef __ASSUME_PRIVATE_FUTEX
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# define __lll_private_flag(fl, private) \
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(((fl) | FUTEX_PRIVATE_FLAG) ^ (private))
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# else
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# define __lll_private_flag(fl, private) \
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(__builtin_constant_p (private) \
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? ((private) == 0 \
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? ((fl) | THREAD_GETMEM (THREAD_SELF, header.private_futex)) \
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: (fl)) \
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: ((fl) | (((private) ^ FUTEX_PRIVATE_FLAG) \
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& THREAD_GETMEM (THREAD_SELF, header.private_futex))))
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# endif
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#endif
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#define lll_futex_syscall(nargs, futexp, op, ...) \
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({ \
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INTERNAL_SYSCALL_DECL (__err); \
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long int __ret = INTERNAL_SYSCALL (futex, __err, nargs, futexp, op, \
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__VA_ARGS__); \
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(__glibc_unlikely (INTERNAL_SYSCALL_ERROR_P (__ret, __err)) \
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? -INTERNAL_SYSCALL_ERRNO (__ret, __err) : 0); \
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})
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#define lll_futex_wait(futexp, val, private) \
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lll_futex_timed_wait (futexp, val, NULL, private)
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#define lll_futex_timed_wait(futexp, val, timeout, private) \
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lll_futex_syscall (4, futexp, \
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__lll_private_flag (FUTEX_WAIT, private), \
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val, timeout)
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#define lll_futex_timed_wait_bitset(futexp, val, timeout, clockbit, private) \
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lll_futex_syscall (6, futexp, \
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__lll_private_flag (FUTEX_WAIT_BITSET | (clockbit), \
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private), \
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val, timeout, NULL /* Unused. */, \
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FUTEX_BITSET_MATCH_ANY)
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#define lll_futex_wake(futexp, nr, private) \
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lll_futex_syscall (4, futexp, \
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__lll_private_flag (FUTEX_WAKE, private), nr, 0)
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/* Returns non-zero if error happened, zero if success. */
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#define lll_futex_requeue(futexp, nr_wake, nr_move, mutex, val, private) \
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lll_futex_syscall (6, futexp, \
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__lll_private_flag (FUTEX_CMP_REQUEUE, private), \
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nr_wake, nr_move, mutex, val)
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/* Returns non-zero if error happened, zero if success. */
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#define lll_futex_wake_unlock(futexp, nr_wake, nr_wake2, futexp2, private) \
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lll_futex_syscall (6, futexp, \
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__lll_private_flag (FUTEX_WAKE_OP, private), \
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nr_wake, nr_wake2, futexp2, \
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FUTEX_OP_CLEAR_WAKE_IF_GT_ONE)
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/* Priority Inheritance support. */
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#define lll_futex_wait_requeue_pi(futexp, val, mutex, private) \
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lll_futex_timed_wait_requeue_pi (futexp, val, NULL, 0, mutex, private)
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#define lll_futex_timed_wait_requeue_pi(futexp, val, timeout, clockbit, \
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mutex, private) \
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lll_futex_syscall (5, futexp, \
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__lll_private_flag (FUTEX_WAIT_REQUEUE_PI \
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| (clockbit), private), \
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val, timeout, mutex)
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#define lll_futex_cmp_requeue_pi(futexp, nr_wake, nr_move, mutex, \
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val, private) \
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lll_futex_syscall (6, futexp, \
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__lll_private_flag (FUTEX_CMP_REQUEUE_PI, \
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private), \
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nr_wake, nr_move, mutex, val)
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#endif /* !__ASSEMBLER__ */
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#endif /* lowlevellock-futex.h */
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