On Fri, Oct 24, 2014 at 10:58:07AM +0200, Michal Hocko wrote: > On Thu 23-10-14 14:19:29, Johannes Weiner wrote: > > On Thu, Oct 23, 2014 at 06:47:45PM +0200, Jan Kara wrote: > > > 'curr' pointer in task_in_mem_cgroup() can be NULL when we race with > > > somebody clearing task->mm. Check for it before dereferencing the > > > pointer. > > > > If task->mm is already NULL, we fall back to mem_cgroup_from_task(), > > which definitely returns a memcg unless you pass NULL in there. So I > > don't see how that could happen, and the NULL checks in the fallback > > branch as well as in __mem_cgroup_same_or_subtree seem bogus to me. > > It came from 3a981f482cc2 (memcg: fix use_hierarchy css_is_ancestor oops > regression). I do not see mem_cgroup_same_or_subtree called from > page_referenced path so it is probably gone. It's still there in invalid_page_referenced_vma(). And it can still pass NULL. > task_in_mem_cgroup is just confused because curr can never be NULL as > the task is never NULL. That's correct. My patches to clean all this up have been stress-tested over night, I will send them out in a jiffy. Thanks -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>