Re: [Xen-devel] [PATCH] xen-blkfront: fix kernel panic with negotiate_mq error path

[Manjunath Patil]

On 10/30/2018 3:39 AM, Roger Pau Monnà wrote:

> On Mon, Oct 29, 2018 at 11:31:56AM -0700, Manjunath Patil wrote:
> > info->nr_rings isn't adjusted in case of ENOMEM error from
> > negotiate_mq(). This leads to kernel panic in error path.
> >
> > Typical call stack involving panic -
> >   #8 page_fault at ffffffff8175936f
> >      [exception RIP: blkif_free_ring+33]
> >      RIP: ffffffffa0149491  RSP: ffff8804f7673c08  RFLAGS: 00010292
> >   ...
> >   #9 blkif_free at ffffffffa0149aaa [xen_blkfront]
> >   #10 talk_to_blkback at ffffffffa014c8cd [xen_blkfront]
> >   #11 blkback_changed at ffffffffa014ea8b [xen_blkfront]
> >   #12 xenbus_otherend_changed at ffffffff81424670
> >   #13 backend_changed at ffffffff81426dc3
> >   #14 xenwatch_thread at ffffffff81422f29
> >   #15 kthread at ffffffff810abe6a
> >   #16 ret_from_fork at ffffffff81754078
> >
> > Though either of my changes avoid the panic, I included both the
> > changes. This issue got introduced with "7ed8ce1 xen-blkfront: move
> > negotiate_mq to cover all cases of new VBDs"
> >
> > Signed-off-by: Manjunath Patil <manjunath.b.patil@xxxxxxxxxx>
> > ---
> >   drivers/block/xen-blkfront.c |    7 +++++--
> >   1 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> > index 429d201..dc8fe25 100644
> > --- a/drivers/block/xen-blkfront.c
> > +++ b/drivers/block/xen-blkfront.c
> > @@ -1350,8 +1350,10 @@ static void blkif_free(struct blkfront_info *info, int suspend)
> >   	if (info->rq)
> >   		blk_mq_stop_hw_queues(info->rq);
> >   
> > -	for (i = 0; i < info->nr_rings; i++)
> > -		blkif_free_ring(&info->rinfo[i]);
> > +	if (info->rinfo) {
> > +		for (i = 0; i < info->nr_rings; i++)
> > +			blkif_free_ring(&info->rinfo[i]);
> > +	}
> I don't see the point in the if case here, you already fixed it by
> setting the nr_rings value which I think it's the correct way of
> fixing it.
>
> Thanks, Roger.
Thank you Roger for your comments.
I will exclude this change and send for review again.

-Thanks,
Manjunath