On 05/15, Peter Zijlstra wrote: > > > > Afaict the whole .owner=NULL thing in release already stops the spinners > > > > Not really, the new writer will spin in this case, afaics. > > > > But this is another problem and probably we do not care. The new writer is > > almost impossible in this particular case, another freeze_super() should > > notice frozen != SB_UNFROZEN and return EBUSY. > > rwsem_spin_on_owner() checks rwsem_owner_is_writer(), which does owner > && owner != RWSEM_READER_OWNED, which will fail for !owner. Yep. So rwsem_spin_on_owner() goes to "out:" and returns !rwsem_owner_is_reader() == T. IOW, afaics owner == NULL means "spin unconditionally", I guess this is for the case when the new writer is going to do rwsem_set_owner() or up_write() has already called rwsem_clear_owner() but didn't do up_write() yet. Probably makes sense, but the code is not very clean, > Or am I completely confused again? Or me, I am not sure. Oleg.
