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.
