xen-blkfront: fix kernel panic with negotiate_mq error path
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
Cc: stable@vger.kernel.org
Fixes: 7ed8ce1c5fc7 ("xen-blkfront: move negotiate_mq to cover all cases of new VBDs")
Signed-off-by: Manjunath Patil <manjunath.b.patil@oracle.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Juergen Gross <jgross@suse.com>