On Wed, May 27, 2015 at 08:35:32AM +1000, NeilBrown wrote:
> On Tue, 26 May 2015 11:16:47 -0700 Shaohua Li <shli@xxxxxxxxxx> wrote:
>
> > On Sat, May 23, 2015 at 10:26:40AM +1000, NeilBrown wrote:
> > > On Fri, 22 May 2015 16:44:02 -0700 Shaohua Li <shli@xxxxxxxxxx> wrote:
> > >
> > > > On Fri, May 22, 2015 at 03:30:58PM +1000, NeilBrown wrote:
> > > > > If a stripe is a member of a batch, but not the head, it must
> > > > > not be handled separately from the rest of the batch.
> > > > >
> > > > > 'clear_batch_ready()' handles this requirement to some
> > > > > extent but not completely. If a member is passed to handle_stripe()
> > > > > a second time it returns '0' indicating the stripe can be handled,
> > > > > which is wrong.
> > > > > So add an extra test.
> > > > >
> > > > > Signed-off-by: NeilBrown <neilb@xxxxxxx>
> > > > > ---
> > > > > drivers/md/raid5.c | 6 +++++-
> > > > > 1 file changed, 5 insertions(+), 1 deletion(-)
> > > > >
> > > > > diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> > > > > index c3ccefbd4fe7..9a803b735848 100644
> > > > > --- a/drivers/md/raid5.c
> > > > > +++ b/drivers/md/raid5.c
> > > > > @@ -4192,9 +4192,13 @@ static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
> > > > >
> > > > > static int clear_batch_ready(struct stripe_head *sh)
> > > > > {
> > > > > + /* Return '1' if this is a member of batch, or
> > > > > + * '0' if it is a lone stripe or a head which can now be
> > > > > + * handled.
> > > > > + */
> > > > > struct stripe_head *tmp;
> > > > > if (!test_and_clear_bit(STRIPE_BATCH_READY, &sh->state))
> > > > > - return 0;
> > > > > + return (sh->batch_head && sh->batch_head != sh);
> > > > > spin_lock(&sh->stripe_lock);
> > > > > if (!sh->batch_head) {
> > > > > spin_unlock(&sh->stripe_lock);
> > > >
> > > > which case can this happen in?
> > >
> > > It definitely happens as I had reliable problems until I added this fix.
> > > 'retry_aligned_read()' can call handle_stripe() on any stripe at any time,
> > > but I doubt that would apply. I might try putting a warn-on there and see if
> > > it provides any hints.
> > >
> > > >
> > > > Patches look good. But I'm not in Fusionio any more, so can't check the
> > > > performance in big raid array with fast flash cards. I'm doing some tests here.
> > > > I hit a warning in break_stripe_batch_list, STRIPE_BIT_DELAY is set in the
> > > > stripe state. I'm checking the reason, but if you have thoughts I can try
> > > > immediately, please let me know.
> > >
> > > I got STRIPE_BIT_DELAY a few times. That was the main reason for
> > >
> > > md/raid5: ensure whole batch is delayed for all required bitmap updates.
> > >
> > > and they went away after I got that patch right.
> > >
> > > Maybe there is a race in there..
> > >
> > > If you can reproduce it, maybe WARN whenever STRIPE_BIT_DELAY gets set on a
> > > stripe with ->batch_head.
> >
> > Ok, there is a race in add_stripe_bio(). We unlocked the stripe_lock to set the
> > BIT_DELAY. After the unlock, the stripe might be added to a batch,
> > stripe_add_to_batch_list didn't clear the bit. Holding the lock in
> > add_stripe_bio and checking ->batch_head again when we set the bit should fix
> > the issue.
>
> We can't hold a spin_lock over bitmap_startwrite(), and we really need to
> make sure the write doesn't start until bitmap_startwrite has completed.
> So we need to keep the stripe_head out of any batch during that time.
> So I've added an extra state bit.
>
> Could you please review and possibly test the patch below?
>
> >
> > And STRIPE_ON_UNPLUG_LIST and STRIPE_ON_RELEASE_LIST are set is legit in
> > break_stripe_batch_list(), they should be removed from the WARN_ON_ONCE().
>
> Yes, you are right. Thanks.
>
> >
> > Thanks,
> > Shaohua
>
> Thanks,
> NeilBrown
>
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index 041341c66ae5..89d6faafffda 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -760,6 +760,7 @@ static void unlock_two_stripes(struct stripe_head *sh1, struct stripe_head *sh2)
> static bool stripe_can_batch(struct stripe_head *sh)
> {
> return test_bit(STRIPE_BATCH_READY, &sh->state) &&
> + !test_bit(STRIPE_BITMAP_PENDING, &sh->state) &&
> is_full_stripe_write(sh);
> }
>
> @@ -3007,14 +3008,18 @@ static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx,
> pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
> (unsigned long long)(*bip)->bi_iter.bi_sector,
> (unsigned long long)sh->sector, dd_idx);
> - spin_unlock_irq(&sh->stripe_lock);
>
> if (conf->mddev->bitmap && firstwrite) {
> + set_bit(STRIPE_BITMAP_PENDING, &sh->state);
> + spin_unlock_irq(&sh->stripe_lock);
> bitmap_startwrite(conf->mddev->bitmap, sh->sector,
> STRIPE_SECTORS, 0);
> + spin_lock_irq(&sh->stripe_lock);
> + clear_bit(STRIPE_BITMAP_PENDING, &sh->state);
> sh->bm_seq = conf->seq_flush+1;
> set_bit(STRIPE_BIT_DELAY, &sh->state);
> }
> + spin_lock_irq(&sh->stripe_lock);
should be unlock here. I'll report back if anything is wrong.
Thanks,
Shaohua
--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
