From: Stefano Garzarella <sgarzare@redhat.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org, Christoph Hellwig <hch@lst.de>,
Changpeng Liu <changpeng.liu@intel.com>,
Daniel Verkamp <dverkamp@chromium.org>,
"Michael S . Tsirkin" <mst@redhat.com>,
Stefan Hajnoczi <stefanha@redhat.com>
Subject: Re: [PATCH 2/2] block: virtio_blk: fix handling single range discard request
Date: Tue, 11 Aug 2020 16:16:43 +0200 [thread overview]
Message-ID: <20200811141643.5s7s3ktpr3src64d@steredhat> (raw)
In-Reply-To: <20200811134326.GA2266621@T590>
On Tue, Aug 11, 2020 at 09:43:26PM +0800, Ming Lei wrote:
> On Tue, Aug 11, 2020 at 03:39:25PM +0200, Stefano Garzarella wrote:
> > On Tue, Aug 11, 2020 at 09:09:53PM +0800, Ming Lei wrote:
> > > On Tue, Aug 11, 2020 at 02:30:44PM +0200, Stefano Garzarella wrote:
> > > > Hi Ming,
> > > >
> > > > On Tue, Aug 11, 2020 at 05:21:34PM +0800, Ming Lei wrote:
> > > > > 1f23816b8eb8 ("virtio_blk: add discard and write zeroes support") starts
> > > > > to support multi-range discard for virtio-blk. However, the virtio-blk
> > > > > disk may report max discard segment as 1, at least that is exactly what
> > > > > qemu is doing.
> > > > >
> > > > > So far, block layer switches to normal request merge if max discard segment
> > > > > limit is 1, and multiple bios can be merged to single segment. This way may
> > > > > cause memory corruption in virtblk_setup_discard_write_zeroes().
> > > > >
> > > > > Fix the issue by handling single max discard segment in straightforward
> > > > > way.
> > > > >
> > > > > Signed-off-by: Ming Lei <ming.lei@redhat.com>
> > > > > Fixes: 1f23816b8eb8 ("virtio_blk: add discard and write zeroes support")
> > > > > Cc: Christoph Hellwig <hch@lst.de>
> > > > > Cc: Changpeng Liu <changpeng.liu@intel.com>
> > > > > Cc: Daniel Verkamp <dverkamp@chromium.org>
> > > > > Cc: Michael S. Tsirkin <mst@redhat.com>
> > > > > Cc: Stefan Hajnoczi <stefanha@redhat.com>
> > > > > ---
> > > > > drivers/block/virtio_blk.c | 23 +++++++++++++++--------
> > > > > 1 file changed, 15 insertions(+), 8 deletions(-)
> > > > >
> > > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > > index 63b213e00b37..05b01903122b 100644
> > > > > --- a/drivers/block/virtio_blk.c
> > > > > +++ b/drivers/block/virtio_blk.c'
> > > > > @@ -126,14 +126,21 @@ static int virtblk_setup_discard_write_zeroes(struct request *req, bool unmap)
> > > > > if (!range)
> > > > > return -ENOMEM;
> > > >
> > > > We are allocating the 'range' array to contain 'segments' elements.
> > > > When queue_max_discard_segments() returns 1, should we limit 'segments'
> > > > to 1?
> > >
> > > That is block layer's responsibility to make sure that 'segments' is <=
> > > 1, and we can double check & warn here.
> >
> > So, IIUC, the number of bio in a request may not be the same as
> > the return value of blk_rq_nr_discard_segments(). Is it right?
>
> In case that queue_max_discard_segments() is 1, it is right. If
> queue_max_discard_segments() is > 1, nr_range is supposed to be
> same with number of bios in a request.
Got it. Thanks for clarify.
In the meantime I took a look at nvme_setup_discard() and there is
WARN_ON_ONCE(n != segments), maybe we should do the same.
Thanks,
Stefano
prev parent reply other threads:[~2020-08-11 14:17 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-11 9:21 [PATCH 0/2] block: fix discard merge for single max discard segment Ming Lei
2020-08-11 9:21 ` [PATCH 1/2] block: respect queue limit of " Ming Lei
2020-08-11 9:21 ` [PATCH 2/2] block: virtio_blk: fix handling single range discard request Ming Lei
2020-08-11 12:30 ` Stefano Garzarella
2020-08-11 13:09 ` Ming Lei
2020-08-11 13:39 ` Stefano Garzarella
2020-08-11 13:43 ` Ming Lei
2020-08-11 14:16 ` Stefano Garzarella [this message]
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