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| author | Carlos O'Donell <carlos@systemhalted.org> | 2016-10-26 00:00:13 -0400 |
|---|---|---|
| committer | Carlos O'Donell <carlos@systemhalted.org> | 2016-10-26 00:00:13 -0400 |
| commit | abff18c0c6055ca5d1cd46923fd1205c057139a5 (patch) | |
| tree | ac538e66a01817613655e12cd17222e67b24e3ed | |
| parent | cd74aa4d5ccae1ae9d815ae7088f06d6fc4aaffc (diff) | |
| download | glibc-abff18c0c6055ca5d1cd46923fd1205c057139a5.tar.gz glibc-abff18c0c6055ca5d1cd46923fd1205c057139a5.tar.xz glibc-abff18c0c6055ca5d1cd46923fd1205c057139a5.zip | |
Fix atomic_fetch_xor_release.
No code uses atomic_fetch_xor_release except for the upcoming conditional variable rewrite. Therefore there is no user visible bug here. The use of atomic_compare_and_exchange_bool_rel is removed (since it doesn't exist anymore), and is replaced by atomic_compare_exchange_weak_release. We use weak_release because it provides better performance in the loop (the weak semantic) and because the xor is release MO (the release semantic). We don't reload expected in the loop because atomic_compare_and_exchange_weak_release does this for us as part of the CAS failure. It is otherwise a fairly plain conversion that fixes building the new condvar for 32-bit x86. Passes all regression tests for x86.
| -rw-r--r-- | ChangeLog | 6 | ||||
| -rw-r--r-- | include/atomic.h | 19 |
2 files changed, 17 insertions, 8 deletions
diff --git a/ChangeLog b/ChangeLog index 6b8763f95a..9c4d06fdc3 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,3 +1,9 @@ +2016-10-26 Carlos O'Donell <carlos@redhat.com> + + * include/atomic.h + [USE_COMPILER_ATOMIC_BUILTINS && !atomic_fetch_xor_release] + (atomic_fetch_xor_release): Use atomic_compare_exchange_weak_release. + 2016-10-25 Rajalakshmi Srinivasaraghavan <raji@linux.vnet.ibm.com> * stdlib/Makefile (tests): Add tst-strfrom and tst-strfrom-locale. diff --git a/include/atomic.h b/include/atomic.h index 5a8e7e7966..c8b46649c5 100644 --- a/include/atomic.h +++ b/include/atomic.h @@ -777,18 +777,21 @@ void __atomic_link_error (void); # endif # ifndef atomic_fetch_xor_release +/* Failing the atomic_compare_exchange_weak_release reloads the value in + __atg104_expected, so we need only do the XOR again and retry. */ # define atomic_fetch_xor_release(mem, operand) \ - ({ __typeof (*(mem)) __atg104_old; \ - __typeof (mem) __atg104_memp = (mem); \ + ({ __typeof (mem) __atg104_memp = (mem); \ + __typeof (*(mem)) __atg104_expected = (*__atg104_memp); \ + __typeof (*(mem)) __atg104_desired; \ __typeof (*(mem)) __atg104_op = (operand); \ \ do \ - __atg104_old = (*__atg104_memp); \ - while (__builtin_expect \ - (atomic_compare_and_exchange_bool_rel ( \ - __atg104_memp, __atg104_old ^ __atg104_op, __atg104_old), 0));\ - \ - __atg104_old; }) + __atg104_desired = __atg104_expected ^ __atg104_op; \ + while (__glibc_unlikely \ + (atomic_compare_exchange_weak_release ( \ + __atg104_memp, &__atg104_expected, __atg104_desired) \ + == 0)); \ + __atg104_expected; }) #endif #endif /* !USE_ATOMIC_COMPILER_BUILTINS */ |