On 05/05/2017 12:36, Stefan Hajnoczi wrote: > On Thu, Apr 20, 2017 at 02:00:57PM +0200, Paolo Bonzini wrote: >> @@ -410,6 +442,18 @@ int bdrv_get_dirty(BlockDriverState *bs, >> BdrvDirtyBitmap *bitmap, >> } >> } >> >> +int bdrv_get_dirty(BlockDriverState *bs, BdrvDirtyBitmap *bitmap, >> + int64_t sector) > > Is it a good idea to offer an unlocked bdrv_get_dirty() API? It > encourages non-atomic access to the bitmap, e.g. > > if (bdrv_get_dirty()) { > ...do something outside the lock... > bdrv_reset_dirty_bitmap(); > } > > The unlocked API should be test-and-set/clear instead so that callers > automatically avoid race conditions.
I'm not sure it's possible to implement atomic test and clear for HBitmap. But I can look into removing unlocked bdrv_get_dirty, the only user is block migration. >> diff --git a/block/mirror.c b/block/mirror.c >> index dc227a2..6a5b0f8 100644 >> --- a/block/mirror.c >> +++ b/block/mirror.c >> @@ -344,10 +344,12 @@ static uint64_t coroutine_fn >> mirror_iteration(MirrorBlockJob *s) >> >> sector_num = bdrv_dirty_iter_next(s->dbi); >> if (sector_num < 0) { >> + bdrv_dirty_bitmap_lock(s->dirty_bitmap); > > bdrv_dirty_iter_next() is listed under "functions that require manual > locking" but it's being called outside of the lock. Thanks, will fix. Paolo