diff options
Diffstat (limited to 'sysdeps/nptl/lowlevellock.h')
| -rw-r--r-- | sysdeps/nptl/lowlevellock.h | 20 |
1 files changed, 15 insertions, 5 deletions
diff --git a/sysdeps/nptl/lowlevellock.h b/sysdeps/nptl/lowlevellock.h index 27f41424ea..3890145402 100644 --- a/sysdeps/nptl/lowlevellock.h +++ b/sysdeps/nptl/lowlevellock.h @@ -1,5 +1,5 @@ /* Low-level lock implementation. Generic futex-based version. - Copyright (C) 2005-2015 Free Software Foundation, Inc. + Copyright (C) 2005-2016 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 @@ -191,14 +191,21 @@ extern int __lll_robust_timedlock_wait (int *futex, const struct timespec *, 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. */ + 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); \ + lll_futex_wake (__futex, 1, __private); \ })) #define lll_unlock(futex, private) \ __lll_unlock (&(futex), private) @@ -209,14 +216,17 @@ extern int __lll_robust_timedlock_wait (int *futex, const struct timespec *, that's cast to void. */ /* Unconditionally set FUTEX to 0 (not acquired), releasing the lock. If FUTEX had FUTEX_WAITERS set then wake any waiters. The waiter that acquires the - lock will set FUTEX_WAITERS. */ + lock will set FUTEX_WAITERS. + Evaluate PRIVATE before releasing the lock so that we do not violate the + mutex destruction requirements (see __lll_unlock). */ #define __lll_robust_unlock(futex, private) \ ((void) \ ({ \ int *__futex = (futex); \ + int __private = (private); \ int __oldval = atomic_exchange_rel (__futex, 0); \ if (__glibc_unlikely (__oldval & FUTEX_WAITERS)) \ - lll_futex_wake (__futex, 1, private); \ + lll_futex_wake (__futex, 1, __private); \ })) #define lll_robust_unlock(futex, private) \ __lll_robust_unlock (&(futex), private) |