Re: [patch 02/10 v3] raid5: delayed stripe fix

[Shaohua Li <shli@kernel.org>]

On Mon, Jul 02, 2012 at 10:46:48AM +1000, NeilBrown wrote:
> On Mon, 25 Jun 2012 15:24:49 +0800 Shaohua Li <shli@kernel.org> wrote:
> 
> > There isn't locking setting STRIPE_DELAYED and STRIPE_PREREAD_ACTIVE bits, but
> > the two bits have relationship. A delayed stripe can be moved to hold list only
> > when preread active stripe count is below IO_THRESHOLD. If a stripe has both
> > the bits set, such stripe will be in delayed list and preread count not 0,
> > which will make such stripe never leave delayed list.
> > 
> > Signed-off-by: Shaohua Li <shli@fusionio.com>
> > ---
> >  drivers/md/raid5.c |    4 +++-
> >  1 file changed, 3 insertions(+), 1 deletion(-)
> > 
> > Index: linux/drivers/md/raid5.c
> > ===================================================================
> > --- linux.orig/drivers/md/raid5.c	2012-06-25 14:36:15.964613183 +0800
> > +++ linux/drivers/md/raid5.c	2012-06-25 14:36:57.280096788 +0800
> > @@ -196,12 +196,14 @@ static void __release_stripe(struct r5co
> >  		BUG_ON(!list_empty(&sh->lru));
> >  		BUG_ON(atomic_read(&conf->active_stripes)==0);
> >  		if (test_bit(STRIPE_HANDLE, &sh->state)) {
> > -			if (test_bit(STRIPE_DELAYED, &sh->state))
> > +			if (test_bit(STRIPE_DELAYED, &sh->state) &&
> > +			    !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
> >  				list_add_tail(&sh->lru, &conf->delayed_list);
> >  			else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
> >  				   sh->bm_seq - conf->seq_write > 0)
> >  				list_add_tail(&sh->lru, &conf->bitmap_list);
> >  			else {
> > +				clear_bit(STRIPE_DELAYED, &sh->state);
> >  				clear_bit(STRIPE_BIT_DELAY, &sh->state);
> >  				list_add_tail(&sh->lru, &conf->handle_list);
> >  			}
> 
> Thanks.  I've applied this patch and will submit it upstream shortly.
> 
> Have you actually seen a stripe get trapped with both bits set, or is this
> just a theoretical problem discovered by code inspection?

I print the flags of strip when there is overlap sleep in make_request(), and
found this case, so this is real.

How do you think about the other patches in the series?

Thanks,
Shaohua