Re: [PATCH] xen-blkfront: fix kernel panic with blkfront_remove()

Greg KH
2018-11-09T11:17:07Z

On Thu, Nov 08, 2018 at 04:58:28PM -0800, Manjunath Patil wrote:
> If a hot-attaching device fails inside domU[ex:negotiate_mq() returns
> with ENOMEM] we clear the blkfront_info struct in talk_to_blkback()
>
> When we try to detach the device, blkfront_remove() tries to access
> blkfront_info leading to kernel panic.
>
> Typical call stack involving panic -
> #10 page_fault at ffffffff816f25df
> [exception RIP: blkif_free+46]
> #11 blkfront_remove at ffffffffa004de47 [xen_blkfront]
> #12 xenbus_dev_remove at ffffffff813faa4c
> #13 __device_release_driver at ffffffff814769aa
> #14 device_release_driver at ffffffff81476a63
> #15 bus_remove_device at ffffffff814762eb
> #16 device_del at ffffffff81472684
> #17 device_unregister at ffffffff814727e2
> #18 xenbus_dev_changed at ffffffff813fa89f
> #19 frontend_changed at ffffffff813fca19
> #20 xenwatch_thread at ffffffff813f88f9
> #21 kthread at ffffffff810a486b
> #22 ret_from_fork at ffffffff816ed2a8
>
> Cc: stable@vger.kernel.org
> Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.com>
> ---
> drivers/block/xen-blkfront.c | 3 +++
> 1 files changed, 3 insertions(+), 0 deletions(-)
>
> diff --git a/drivers/block/xen-blkfront.c b/drivers/block/xen-blkfront.c
> index dc8fe25..144cda8 100644
> --- a/drivers/block/xen-blkfront.c
> +++ b/drivers/block/xen-blkfront.c
> @@ -2496,6 +2496,9 @@ static int blkfront_remove(struct xenbus_device *xbdev)
>
> dev_dbg(&xbdev->dev, "%s removed", xbdev->nodename);
>
> + if(!info)
> + return 0;
> +

Always run scripts/checkpatch.pl on your patches so you do not get a
grumpy maintainer telling you to run scripts/checkpatch.pl on your
patches.

thanks,

greg k-h