Re: [PATCH] block: insert a general SMP memory barrier before wake_up_bit()

[Jacob Wen]

On 8/13/20 3:31 PM, Christoph Hellwig wrote:
> On Thu, Aug 13, 2020 at 10:44:38AM +0800, Jacob Wen wrote:
> > wake_up_bit() uses waitqueue_active() that needs the explicit smp_mb().
> Sounds like the barrier should go into wake_up_bit then..

wake_up_bit() doesn't know which one to chose: smp_mb__after_atomic() or 
smp_mb().

> > Signed-off-by: Jacob Wen <jian.w.wen@xxxxxxxxxx>
> > ---
> >   fs/block_dev.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/fs/block_dev.c b/fs/block_dev.c
> > index 0ae656e022fd..e74980848a2a 100644
> > --- a/fs/block_dev.c
> > +++ b/fs/block_dev.c
> > @@ -1175,6 +1175,7 @@ static void bd_clear_claiming(struct block_device *whole, void *holder)
> >   	/* tell others that we're done */
> >   	BUG_ON(whole->bd_claiming != holder);
> >   	whole->bd_claiming = NULL;
> > +	smp_mb();
> >   	wake_up_bit(&whole->bd_claiming, 0);
> >   }
> >   
> > --
> > 2.17.1
> ---end quoted text---