On Mon, Nov 11, 2024 at 4:35 PM Davidlohr Bueso <dave@xxxxxxxxxxxx> wrote: > > On Mon, 11 Nov 2024, Suren Baghdasaryan wrote: > > >@@ -787,7 +893,10 @@ static inline void vma_start_write(struct vm_area_struct *vma) > > * we should use WRITE_ONCE() for cleanliness and to keep KCSAN happy. > > */ > > WRITE_ONCE(vma->vm_lock_seq, mm_lock_seq); > >- up_write(&vma->vm_lock.lock); > >+ /* Write barrier to ensure vm_lock_seq change is visible before count */ > >+ smp_wmb(); > >+ rwsem_release(&vma->vm_lock.dep_map, _RET_IP_); > >+ atomic_set(&vma->vm_lock.count, VMA_LOCK_UNLOCKED); > > Too many barriers here. Just do atomic_set_release and remove that > smp_wmb(). And what you are doing is really ensuring nothing leaks out > of the critical region, so that comment should also be more generic. Uh, yes. I missed that. > > I would expect regression testing to catch this sort of thing. Well, it's in vma_start_write(), which is in the write-locking path. Maybe that's why it's not very visible. > > ... > > > #ifdef CONFIG_PER_VMA_LOCK > >+ struct wait_queue_head vma_writer_wait; > > You might want to use rcuwait here instead, which is much more > optimized for the single waiter requirement vmas have. Thanks for the suggestion! I'll give it a try. > > Thanks, > Davidlohr
