diff options
Diffstat (limited to 'sysdeps/unix/sysv/linux/x86/elision-trylock.c')
| -rw-r--r-- | sysdeps/unix/sysv/linux/x86/elision-trylock.c | 20 |
1 files changed, 12 insertions, 8 deletions
diff --git a/sysdeps/unix/sysv/linux/x86/elision-trylock.c b/sysdeps/unix/sysv/linux/x86/elision-trylock.c index 65d9c18584..7c55fb878e 100644 --- a/sysdeps/unix/sysv/linux/x86/elision-trylock.c +++ b/sysdeps/unix/sysv/linux/x86/elision-trylock.c @@ -1,5 +1,5 @@ /* elision-trylock.c: Lock eliding trylock for pthreads. - Copyright (C) 2013-2016 Free Software Foundation, Inc. + Copyright (C) 2013-2018 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 @@ -36,8 +36,10 @@ __lll_trylock_elision (int *futex, short *adapt_count) return an error. */ _xabort (_ABORT_NESTED_TRYLOCK); - /* Only try a transaction if it's worth it. */ - if (*adapt_count <= 0) + /* Only try a transaction if it's worth it. See __lll_lock_elision for + why we need atomic accesses. Relaxed MO is sufficient because this is + just a hint. */ + if (atomic_load_relaxed (adapt_count) <= 0) { unsigned status; @@ -55,16 +57,18 @@ __lll_trylock_elision (int *futex, short *adapt_count) if (!(status & _XABORT_RETRY)) { /* Internal abort. No chance for retry. For future - locks don't try speculation for some time. */ - if (*adapt_count != aconf.skip_trylock_internal_abort) - *adapt_count = aconf.skip_trylock_internal_abort; + locks don't try speculation for some time. See above for MO. */ + if (atomic_load_relaxed (adapt_count) + != aconf.skip_lock_internal_abort) + atomic_store_relaxed (adapt_count, aconf.skip_lock_internal_abort); } /* Could do some retries here. */ } else { - /* Lost updates are possible, but harmless. */ - (*adapt_count)--; + /* Lost updates are possible but harmless (see above). */ + atomic_store_relaxed (adapt_count, + atomic_load_relaxed (adapt_count) - 1); } return lll_trylock (*futex); |