diff options
| -rw-r--r-- | docs/devel/atomics.txt | 1 | ||||
| -rw-r--r-- | include/qemu/atomic.h | 8 | ||||
| -rw-r--r-- | memory.c | 12 |
3 files changed, 17 insertions, 4 deletions
diff --git a/docs/devel/atomics.txt b/docs/devel/atomics.txt index 048e5f23cb..10c5fa37e8 100644 --- a/docs/devel/atomics.txt +++ b/docs/devel/atomics.txt @@ -64,6 +64,7 @@ operations: typeof(*ptr) atomic_fetch_and(ptr, val) typeof(*ptr) atomic_fetch_or(ptr, val) typeof(*ptr) atomic_fetch_xor(ptr, val) + typeof(*ptr) atomic_fetch_inc_nonzero(ptr) typeof(*ptr) atomic_xchg(ptr, val) typeof(*ptr) atomic_cmpxchg(ptr, old, new) diff --git a/include/qemu/atomic.h b/include/qemu/atomic.h index b6b62fb771..d73c9e14d7 100644 --- a/include/qemu/atomic.h +++ b/include/qemu/atomic.h @@ -442,4 +442,12 @@ } while(0) #endif +#define atomic_fetch_inc_nonzero(ptr) ({ \ + typeof_strip_qual(*ptr) _oldn = atomic_read(ptr); \ + while (_oldn && atomic_cmpxchg(ptr, _oldn, _oldn + 1) != _oldn) { \ + _oldn = atomic_read(ptr); \ + } \ + _oldn; \ +}) + #endif /* QEMU_ATOMIC_H */ @@ -294,9 +294,9 @@ static void flatview_destroy(FlatView *view) g_free(view); } -static void flatview_ref(FlatView *view) +static bool flatview_ref(FlatView *view) { - atomic_inc(&view->ref); + return atomic_fetch_inc_nonzero(&view->ref) > 0; } static void flatview_unref(FlatView *view) @@ -773,8 +773,12 @@ static FlatView *address_space_get_flatview(AddressSpace *as) FlatView *view; rcu_read_lock(); - view = atomic_rcu_read(&as->current_map); - flatview_ref(view); + do { + view = atomic_rcu_read(&as->current_map); + /* If somebody has replaced as->current_map concurrently, + * flatview_ref returns false. + */ + } while (!flatview_ref(view)); rcu_read_unlock(); return view; } |