On Sat, Sep 05, 2015 at 04:34:39PM +0100, Richard W.M. Jones wrote: > [ 52.259269] BUG: unable to handle kernel NULL pointer dereference at 00000000000009c8 > [ 52.259269] IP: [<ffffffff813f8b10>] __blkg_lookup+0x40/0xe0 And also: $ addr2line -e /usr/lib/debug/lib/modules/4.3.0-0.rc0.git7.1.rwmj3.fc24.x86_64/vmlinux ffffffff813f8b10 /usr/src/debug/kernel-4.2.fc24/linux-4.3.0-0.rc0.git7.1.rwmj3.fc24.x86_64/block/blk-cgroup.c:158 152 /* 153 * Hint didn't match. Look up from the radix tree. Note that the 154 * hint can only be updated under queue_lock as otherwise @blkg 155 * could have already been removed from blkg_tree. The caller is 156 * responsible for grabbing queue_lock if @update_hint. 157 */ 158 blkg = radix_tree_lookup(&blkcg->blkg_tree, q->id); 159 if (blkg && blkg->q == q) { 160 if (update_hint) { 161 lockdep_assert_held(q->queue_lock); 162 rcu_assign_pointer(blkcg->blkg_hint, blkg); 163 } 164 return blkg; 165 } Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com libguestfs lets you edit virtual machines. Supports shell scripting, bindings from many languages. http://libguestfs.org -- To unsubscribe from this list: send the line "unsubscribe cgroups" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html