linux-kernel - Re: [PULL REQUEST] md bug fixes and minor improvements

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Date:	Fri, 1 Aug 2008 20:29:00 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Dan Williams <dan.j.williams@...el.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Neil Brown <neilb@...e.de>, Arthur Jones <ajones@...erbed.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-raid@...r.kernel.org, "Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: [PULL REQUEST] md bug fixes and minor improvements

On Fri, Aug 01 2008, Dan Williams wrote:
> 
> On Fri, 2008-08-01 at 10:40 -0700, Jens Axboe wrote:
> > On Fri, Aug 01 2008, Dan Williams wrote:
> > >
> > > On Fri, 2008-08-01 at 19:22 +0200, Jens Axboe wrote:
> > > > It is a bit asymmetrical, largely due to the fact that the ->unplug_fn()
> > > > itself grabs the lock. The below patch should fix it, since Neil has
> > > > added a proper queue lock to the md queues. If someone can confirm that
> > > > this fixes it, I'll queue up a patch with proper descriptions.
> > > >
> > > > > I guess Jens is gone too..
> > > >
> > > > I'm back, just been busy this week :-)
> > > >
> > > > diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
> > > > index 621a272..f19b52f 100644
> > > > --- a/drivers/md/bitmap.c
> > > > +++ b/drivers/md/bitmap.c
> > > > @@ -1234,7 +1234,9 @@ int bitmap_startwrite(struct bitmap *bitmap, sector_t offset, unsigned long sect
> > > >             case 0:
> > > >                     bitmap_file_set_bit(bitmap, offset);
> > > >                     bitmap_count_page(bitmap,offset, 1);
> > > > +                   spin_lock_irq(&bitmap->mddev->queue->queue_lock);
> > > >                     blk_plug_device(bitmap->mddev->queue);
> > > > +                   spin_unlock_irq(&bitmap->mddev->queue->queue_lock);
> > > >                     /* fall through */
> > > >             case 1:
> > > >                     *bmc = 2;
> > > >
> > >
> > > We also need to protect the blk_plug_device call a few lines down (and
> > > an obvious compile fix).
> > 
> > Old source I guess, just one blk_plug_device() in the copy I have here.
> > Just checked latest git, still just one blk_plug_device(), are you
> > diffing against -mm or something like that? Or linux-next?
> 
> No, my mistake... I crossed my eyes and misread your patch as protecting
> blk_unplug() a few lines up, sorry.

Ah, didn't read that closely in your patch, that would get you into
trouble :-)

> > And queue_lock is of course a pointer, I didn't even compile the
> > thing... Thanks for the updated variant!
> 
> I have verified that:
> 
> 	mdadm --create /dev/md0 /dev/sd[bc] -n 2 -l 1 --bitmap=internal
> 	dd if=/dev/zero of=/dev/md0 bs=1024k count=1
> 
> ...no longer triggers the warning with your fix.

Goodie, thanks!

-- 
Jens Axboe

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