On Mon, 2 Jul 2012 08:49:55 +0800 Shaohua Li <shli@xxxxxxxxxx> wrote:
> On Mon, Jul 02, 2012 at 10:46:48AM +1000, NeilBrown wrote:
> > On Mon, 25 Jun 2012 15:24:49 +0800 Shaohua Li <shli@xxxxxxxxxx> 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@xxxxxxxxxxxx>
> > > ---
> > > 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.
OK, thanks.
>
> How do you think about the other patches in the series?
I'll let you know shortly.
NeilBrown
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