LineageOS/android_external_libcxx
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

[libcxx] Fix a data race in call_once

Browse Source 
call_once is using relaxed atomic load to perform double-checked locking, which contains a data race. The fast-path load has to be an acquire atomic load.

Differential Revision: https://reviews.llvm.org/D24028



git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@280621 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Kuba Brecka
2016-09-04 09:55:12 +00:00
parent 226cd0674e
commit 4dbd4fcf86
3 changed files with 15 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
src/mutex.cpp
View File

@@ -199,9 +199,6 @@ static __libcpp_mutex_t mut = _LIBCPP_MUTEX_INITIALIZER;
static __libcpp_condvar_t cv = _LIBCPP_CONDVAR_INITIALIZER;
#endif
/// NOTE: Changes to flag are done via relaxed atomic stores
/// even though the accesses are protected by a mutex because threads
/// just entering 'call_once` concurrently read from flag.
void
__call_once(volatile unsigned long& flag, void* arg, void(*func)(void*))
{
@@ -238,7 +235,7 @@ __call_once(volatile unsigned long& flag, void* arg, void(*func)(void*))
__libcpp_mutex_unlock(&mut);
func(arg);
__libcpp_mutex_lock(&mut);
__libcpp_relaxed_store(&flag, ~0ul);
__libcpp_atomic_store(&flag, ~0ul, _AO_Release);
__libcpp_mutex_unlock(&mut);
__libcpp_condvar_broadcast(&cv);
#ifndef _LIBCPP_NO_EXCEPTIONS