On Fri, 19 Aug 2011 19:51:33 +0900 Mitsuo Hayasaka <mitsuo.hayasaka.hu@xxxxxxxxxxx> wrote: > The /proc/vmallocinfo shows information about vmalloc allocations in vmlist > that is a linklist of vm_struct. It, however, may access pages field of > vm_struct where a page was not allocated, which results in a null pointer > access and leads to a kernel panic. > > Why this happen: > In __vmalloc_area_node(), the nr_pages field of vm_struct are set to the > expected number of pages to be allocated, before the actual pages > allocations. At the same time, when the /proc/vmallocinfo is read, it > accesses the pages field of vm_struct according to the nr_pages field at > show_numa_info(). Thus, a null pointer access happens. > > Patch: > This patch sets nr_pages field of vm_struct AFTER the pages allocations > finished in __vmalloc_area_node(). So, it can avoid accessing the pages > field with unallocated page when show_numa_info() is called. I think this is still just a workaround to fix up the real bug, and that the real bug is that the vm_struct is installed into the vmlist *before* it is fully initialised. It's just wrong to insert an object into a globally-visible list and to then start populating it! If we were instead to fully initialise the vm_struct and *then* insert it into vmlist, the bug is fixed. Also I'd agree with Paul's concern regarding cross-CPU memory ordering. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>