On Tue, Nov 19, 2013 at 07:02:30PM -0700, Jens Axboe wrote:
> On Tue, Nov 19 2013, Jens Axboe wrote:
> > > Looks like a race condition, below works for me, please try.
> > >
> > >
> > > Subject: virtio_blk: fix race condition
> > >
> > > virtqueue_kick() isn't multi-thread safe.
> > >
> > > Signed-off-by: Shaohua Li <s...@fusionio.com>
> > >
> > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > index 588479d..f353959 100644
> > > --- a/drivers/block/virtio_blk.c
> > > +++ b/drivers/block/virtio_blk.c
> > > @@ -204,10 +204,11 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx
> > > *hctx, struct request *req)
> > > virtqueue_kick(vblk->vq);
> > > return BLK_MQ_RQ_QUEUE_BUSY;
> > > }
> > > - spin_unlock_irqrestore(&vblk->vq_lock, flags);
> > >
> > > if (last)
> > > virtqueue_kick(vblk->vq);
> > > + spin_unlock_irqrestore(&vblk->vq_lock, flags);
> > > +
> > > return BLK_MQ_RQ_QUEUE_OK;
> > > }
> >
> > Just stumbled on that too. You need one more, btw, for the sg failure
> > case:
> >
> >
> > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > index 588479d58f52..6a680d4de7f1 100644
> > --- a/drivers/block/virtio_blk.c
> > +++ b/drivers/block/virtio_blk.c
> > @@ -199,15 +199,16 @@ static int virtio_queue_rq(struct blk_mq_hw_ctx
> > *hctx, struct request *req)
> >
> > spin_lock_irqsave(&vblk->vq_lock, flags);
> > if (__virtblk_add_req(vblk->vq, vbr, vbr->sg, num) < 0) {
> > + virtqueue_kick(vblk->vq);
> > spin_unlock_irqrestore(&vblk->vq_lock, flags);
> > blk_mq_stop_hw_queue(hctx);
> > - virtqueue_kick(vblk->vq);
> > return BLK_MQ_RQ_QUEUE_BUSY;
> > }
> > - spin_unlock_irqrestore(&vblk->vq_lock, flags);
> >
> > if (last)
> > virtqueue_kick(vblk->vq);
> > +
> > + spin_unlock_irqrestore(&vblk->vq_lock, flags);
> > return BLK_MQ_RQ_QUEUE_OK;
> > }
>
> Tested successfully here too.
Ah, so it is exactly the problem I suggested it might be. ;)
> Dave, please give it a go, looks like this
> should fix it up for you. Committed here:
>
> http://git.kernel.dk/?p=linux-block.git;a=commit;h=f02b9ac35a47dff745c7637fbc095f01cc03646e
Testing it now. might take a little while to confirm given it had
taken a few iterations of xfstests before I tripped over it...
Cheers,
Dave.
--
Dave Chinner
da...@fromorbit.com
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