Messages in this thread | | | Date | Fri, 18 Feb 2011 14:33:25 +1100 | From | NeilBrown <> | Subject | Re: blk_throtl_exit taking q->queue_lock is problematic |
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On Thu, 17 Feb 2011 22:19:52 -0500 Mike Snitzer <snitzer@redhat.com> wrote:
> On Thu, Feb 17, 2011 at 9:40 PM, NeilBrown <neilb@suse.de> wrote: > > On Thu, 17 Feb 2011 11:59:06 -0500 Vivek Goyal <vgoyal@redhat.com> wrote: > >> So if we do this change for performance reasons, it still makes sense > >> but doing this change because md provided a q->queue_lock and took away that > >> lock without notifying block layer hence we do this change, is still not > >> the right reason, IMHO. > > > > Well...I like that patch, as it makes my life easier.... > > > > But I agree that md is doing something wrong. Now that ->queue_lock is > > always initialised, it is wrong to leave it in a state where it not defined. > > > > So maybe I'll apply this (after testing it a bit. The only reason for taking > > the lock queue_lock in a couple of places is to silence some warnings. > > > > Thanks, > > NeilBrown > > > > > > diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c > > index a23ffa3..909282d 100644 > > --- a/drivers/md/raid1.c > > +++ b/drivers/md/raid1.c > > @@ -959,7 +961,9 @@ static int make_request(mddev_t *mddev, struct bio * bio) > > atomic_inc(&r1_bio->remaining); > > spin_lock_irqsave(&conf->device_lock, flags); > > bio_list_add(&conf->pending_bio_list, mbio); > > + spin_lock(mddev->queue->queue_lock); > > blk_plug_device(mddev->queue); > > + spin_unlock(mddev->queue->queue_lock); > > spin_unlock_irqrestore(&conf->device_lock, flags); > > } > > r1_bio_write_done(r1_bio, bio->bi_vcnt, behind_pages, behind_pages != NULL); > > Noticed an inconsistency, raid10.c's additional locking also protects > the bio_list_add() whereas raid1.c's doesn't. Seems the additional > protection in raid10 isn't needed?
Correct - not needed at all. I put it there because it felt a little cleaner keeping the two 'lock's together like the two 'unlock's. Probably confusing though...
My other though is to stop using the block-layer plugging altogether like I have in RAID5 (Which I needed to do to make it work with DM). Then I wouldn't need to touch queue_lock at all - very tempting.
Thanks for the review.
NeilBrown
> > > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c > > index 3b607b2..60e6cb1 100644 > > --- a/drivers/md/raid10.c > > +++ b/drivers/md/raid10.c > > @@ -970,8 +972,10 @@ static int make_request(mddev_t *mddev, struct bio * bio) > > > > atomic_inc(&r10_bio->remaining); > > spin_lock_irqsave(&conf->device_lock, flags); > > + spin_lock(mddev->queue->queue_lock); > > bio_list_add(&conf->pending_bio_list, mbio); > > blk_plug_device(mddev->queue); > > + spin_unlock(mddev->queue->queue_lock); > > spin_unlock_irqrestore(&conf->device_lock, flags); > > } > >
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