In slab_alloc_node(), after the cpu_slab is assigned, if the task is preempted and moves to another CPU, there's nothing keeping the page and object in sync. The -rt kernel crashed because page was NULL and object was not, and the node_match() dereferences page. Even though the crash happened on -rt, there's nothing that's keeping this from happening on mainline. The easiest fix is to disable interrupts for the entire time from acquiring the current CPU cpu_slab and assigning the object and page. After that, it's fine to allow preemption. Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx> diff --git a/mm/slub.c b/mm/slub.c index ba2ca53..f0681db 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2325,6 +2325,7 @@ static __always_inline void *slab_alloc_node(struct kmem_cache *s, struct kmem_cache_cpu *c; struct page *page; unsigned long tid; + unsigned long flags; if (slab_pre_alloc_hook(s, gfpflags)) return NULL; @@ -2337,7 +2338,10 @@ redo: * enabled. We may switch back and forth between cpus while * reading from one cpu area. That does not matter as long * as we end up on the original cpu again when doing the cmpxchg. + * + * But we need to sync the setting of page and object. */ + local_irq_save(flags); c = __this_cpu_ptr(s->cpu_slab); /* @@ -2347,10 +2351,11 @@ redo: * linked list in between. */ tid = c->tid; - barrier(); object = c->freelist; page = c->page; + local_irq_restore(flags); + if (unlikely(!object || !node_match(page, node))) object = __slab_alloc(s, gfpflags, node, addr, c); -- 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>