mirror of
https://sourceware.org/git/glibc.git
synced 2024-11-26 23:10:06 +00:00
1660901840
On s390 (31bit) if glibc is build with -Os, pthread_join sometimes blocks indefinitely. This is e.g. observable with testcase intl/tst-gettext6. pthread_join is calling lll_wait_tid(tid), which performs the futex-wait syscall in a loop as long as tid != 0 (thread is alive). On s390 (and build with -Os), tid is loaded from memory before comparing against zero and then the tid is loaded a second time in order to pass it to the futex-wait-syscall. If the thread exits in between, then the futex-wait-syscall is called with the value zero and it waits until a futex-wake occurs. As the thread is already exited, there won't be a futex-wake. In lll_wait_tid, the tid is stored to the local variable __tid, which is then used as argument for the futex-wait-syscall. But unfortunately the compiler is allowed to reload the value from memory. With this patch, the tid is loaded with atomic_load_acquire. Then the compiler is not allowed to reload the value for __tid from memory. ChangeLog: [BZ #23137] * sysdeps/nptl/lowlevellock.h (lll_wait_tid): Use atomic_load_acquire to load __tid.
209 lines
9.7 KiB
C
209 lines
9.7 KiB
C
/* Low-level lock implementation. Generic futex-based version.
|
|
Copyright (C) 2005-2018 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/>. */
|
|
|
|
#ifndef _LOWLEVELLOCK_H
|
|
#define _LOWLEVELLOCK_H 1
|
|
|
|
#include <atomic.h>
|
|
#include <lowlevellock-futex.h>
|
|
|
|
/* Low-level locks use a combination of atomic operations (to acquire and
|
|
release lock ownership) and futex operations (to block until the state
|
|
of a lock changes). A lock can be in one of three states:
|
|
0: not acquired,
|
|
1: acquired with no waiters; no other threads are blocked or about to block
|
|
for changes to the lock state,
|
|
>1: acquired, possibly with waiters; there may be other threads blocked or
|
|
about to block for changes to the lock state.
|
|
|
|
We expect that the common case is an uncontended lock, so we just need
|
|
to transition the lock between states 0 and 1; releasing the lock does
|
|
not need to wake any other blocked threads. If the lock is contended
|
|
and a thread decides to block using a futex operation, then this thread
|
|
needs to first change the state to >1; if this state is observed during
|
|
lock release, the releasing thread will wake one of the potentially
|
|
blocked threads.
|
|
|
|
Much of this code takes a 'private' parameter. This may be:
|
|
LLL_PRIVATE: lock only shared within a process
|
|
LLL_SHARED: lock may be shared across processes.
|
|
|
|
Condition variables contain an optimization for broadcasts that requeues
|
|
waiting threads on a lock's futex. Therefore, there is a special
|
|
variant of the locks (whose name contains "cond") that makes sure to
|
|
always set the lock state to >1 and not just 1.
|
|
|
|
Robust locks set the lock to the id of the owner. This allows detection
|
|
of the case where the owner exits without releasing the lock. Flags are
|
|
OR'd with the owner id to record additional information about lock state.
|
|
Therefore the states of robust locks are:
|
|
0: not acquired
|
|
id: acquired (by user identified by id & FUTEX_TID_MASK)
|
|
|
|
The following flags may be set in the robust lock value:
|
|
FUTEX_WAITERS - possibly has waiters
|
|
FUTEX_OWNER_DIED - owning user has exited without releasing the futex. */
|
|
|
|
|
|
/* If LOCK is 0 (not acquired), set to 1 (acquired with no waiters) and return
|
|
0. Otherwise leave lock unchanged and return non-zero to indicate that the
|
|
lock was not acquired. */
|
|
#define lll_trylock(lock) \
|
|
__glibc_unlikely (atomic_compare_and_exchange_bool_acq (&(lock), 1, 0))
|
|
|
|
/* If LOCK is 0 (not acquired), set to 2 (acquired, possibly with waiters) and
|
|
return 0. Otherwise leave lock unchanged and return non-zero to indicate
|
|
that the lock was not acquired. */
|
|
#define lll_cond_trylock(lock) \
|
|
__glibc_unlikely (atomic_compare_and_exchange_bool_acq (&(lock), 2, 0))
|
|
|
|
extern void __lll_lock_wait_private (int *futex) attribute_hidden;
|
|
extern void __lll_lock_wait (int *futex, int private) attribute_hidden;
|
|
|
|
/* This is an expression rather than a statement even though its value is
|
|
void, so that it can be used in a comma expression or as an expression
|
|
that's cast to void. */
|
|
/* The inner conditional compiles to a call to __lll_lock_wait_private if
|
|
private is known at compile time to be LLL_PRIVATE, and to a call to
|
|
__lll_lock_wait otherwise. */
|
|
/* If FUTEX is 0 (not acquired), set to 1 (acquired with no waiters) and
|
|
return. Otherwise, ensure that it is >1 (acquired, possibly with waiters)
|
|
and then block until we acquire the lock, at which point FUTEX will still be
|
|
>1. The lock is always acquired on return. */
|
|
#define __lll_lock(futex, private) \
|
|
((void) \
|
|
({ \
|
|
int *__futex = (futex); \
|
|
if (__glibc_unlikely \
|
|
(atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \
|
|
{ \
|
|
if (__builtin_constant_p (private) && (private) == LLL_PRIVATE) \
|
|
__lll_lock_wait_private (__futex); \
|
|
else \
|
|
__lll_lock_wait (__futex, private); \
|
|
} \
|
|
}))
|
|
#define lll_lock(futex, private) \
|
|
__lll_lock (&(futex), private)
|
|
|
|
|
|
/* This is an expression rather than a statement even though its value is
|
|
void, so that it can be used in a comma expression or as an expression
|
|
that's cast to void. */
|
|
/* Unconditionally set FUTEX to 2 (acquired, possibly with waiters). If FUTEX
|
|
was 0 (not acquired) then return. Otherwise, block until the lock is
|
|
acquired, at which point FUTEX is 2 (acquired, possibly with waiters). The
|
|
lock is always acquired on return. */
|
|
#define __lll_cond_lock(futex, private) \
|
|
((void) \
|
|
({ \
|
|
int *__futex = (futex); \
|
|
if (__glibc_unlikely (atomic_exchange_acq (__futex, 2) != 0)) \
|
|
__lll_lock_wait (__futex, private); \
|
|
}))
|
|
#define lll_cond_lock(futex, private) __lll_cond_lock (&(futex), private)
|
|
|
|
|
|
extern int __lll_timedlock_wait (int *futex, const struct timespec *,
|
|
int private) attribute_hidden;
|
|
|
|
|
|
/* As __lll_lock, but with a timeout. If the timeout occurs then return
|
|
ETIMEDOUT. If ABSTIME is invalid, return EINVAL. */
|
|
#define __lll_timedlock(futex, abstime, private) \
|
|
({ \
|
|
int *__futex = (futex); \
|
|
int __val = 0; \
|
|
\
|
|
if (__glibc_unlikely \
|
|
(atomic_compare_and_exchange_bool_acq (__futex, 1, 0))) \
|
|
__val = __lll_timedlock_wait (__futex, abstime, private); \
|
|
__val; \
|
|
})
|
|
#define lll_timedlock(futex, abstime, private) \
|
|
__lll_timedlock (&(futex), abstime, private)
|
|
|
|
|
|
/* This is an expression rather than a statement even though its value is
|
|
void, so that it can be used in a comma expression or as an expression
|
|
that's cast to void. */
|
|
/* Unconditionally set FUTEX to 0 (not acquired), releasing the lock. If FUTEX
|
|
was >1 (acquired, possibly with waiters), then wake any waiters. The waiter
|
|
that acquires the lock will set FUTEX to >1.
|
|
Evaluate PRIVATE before releasing the lock so that we do not violate the
|
|
mutex destruction requirements. Specifically, we need to ensure that
|
|
another thread can destroy the mutex (and reuse its memory) once it
|
|
acquires the lock and when there will be no further lock acquisitions;
|
|
thus, we must not access the lock after releasing it, or those accesses
|
|
could be concurrent with mutex destruction or reuse of the memory. */
|
|
#define __lll_unlock(futex, private) \
|
|
((void) \
|
|
({ \
|
|
int *__futex = (futex); \
|
|
int __private = (private); \
|
|
int __oldval = atomic_exchange_rel (__futex, 0); \
|
|
if (__glibc_unlikely (__oldval > 1)) \
|
|
lll_futex_wake (__futex, 1, __private); \
|
|
}))
|
|
#define lll_unlock(futex, private) \
|
|
__lll_unlock (&(futex), private)
|
|
|
|
|
|
#define lll_islocked(futex) \
|
|
((futex) != LLL_LOCK_INITIALIZER)
|
|
|
|
|
|
/* Our internal lock implementation is identical to the binary-compatible
|
|
mutex implementation. */
|
|
|
|
/* Initializers for lock. */
|
|
#define LLL_LOCK_INITIALIZER (0)
|
|
#define LLL_LOCK_INITIALIZER_LOCKED (1)
|
|
|
|
|
|
/* The kernel notifies a process which uses CLONE_CHILD_CLEARTID via futex
|
|
wake-up when the clone terminates. The memory location contains the
|
|
thread ID while the clone is running and is reset to zero by the kernel
|
|
afterwards. The kernel up to version 3.16.3 does not use the private futex
|
|
operations for futex wake-up when the clone terminates. */
|
|
#define lll_wait_tid(tid) \
|
|
do { \
|
|
__typeof (tid) __tid; \
|
|
/* We need acquire MO here so that we synchronize \
|
|
with the kernel's store to 0 when the clone \
|
|
terminates. (see above) */ \
|
|
while ((__tid = atomic_load_acquire (&(tid))) != 0) \
|
|
lll_futex_wait (&(tid), __tid, LLL_SHARED); \
|
|
} while (0)
|
|
|
|
extern int __lll_timedwait_tid (int *, const struct timespec *)
|
|
attribute_hidden;
|
|
|
|
/* As lll_wait_tid, but with a timeout. If the timeout occurs then return
|
|
ETIMEDOUT. If ABSTIME is invalid, return EINVAL. */
|
|
#define lll_timedwait_tid(tid, abstime) \
|
|
({ \
|
|
int __res = 0; \
|
|
if ((tid) != 0) \
|
|
__res = __lll_timedwait_tid (&(tid), (abstime)); \
|
|
__res; \
|
|
})
|
|
|
|
|
|
#endif /* lowlevellock.h */
|