From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx147.postini.com [74.125.245.147]) by kanga.kvack.org (Postfix) with SMTP id D594A6B0005 for ; Thu, 17 Jan 2013 19:28:46 -0500 (EST) Message-ID: <1358468924.23211.69.camel@gandalf.local.home> Subject: [RFC][PATCH v2] slub: Keep page and object in sync in slab_alloc_node() From: Steven Rostedt Date: Thu, 17 Jan 2013 19:28:44 -0500 In-Reply-To: <1358468598.23211.67.camel@gandalf.local.home> References: <1358446258.23211.32.camel@gandalf.local.home> <1358447864.23211.34.camel@gandalf.local.home> <0000013c4a69a2cf-1a19a6f6-e6a3-4f06-99a4-10fdd4b9aca2-000000@email.amazonses.com> <1358458996.23211.46.camel@gandalf.local.home> <0000013c4a7e7fbf-c51fd42a-2455-4fec-bb37-915035956f05-000000@email.amazonses.com> <1358462763.23211.57.camel@gandalf.local.home> <1358464245.23211.62.camel@gandalf.local.home> <1358464837.23211.66.camel@gandalf.local.home> <1358468598.23211.67.camel@gandalf.local.home> Content-Type: text/plain; charset="ISO-8859-15" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Christoph Lameter Cc: LKML , linux-mm , Andrew Morton , Pekka Enberg , Matt Mackall , Thomas Gleixner , RT , Clark Williams , John Kacur , "Luis Claudio R. Goncalves" 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 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@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org