From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx174.postini.com [74.125.245.174]) by kanga.kvack.org (Postfix) with SMTP id 8ADD46B0006 for ; Fri, 18 Jan 2013 09:44:57 -0500 (EST) Date: Fri, 18 Jan 2013 14:44:55 +0000 From: Christoph Lameter Subject: Re: [RFC][PATCH v2] slub: Keep page and object in sync in slab_alloc_node() In-Reply-To: <1358468924.23211.69.camel@gandalf.local.home> Message-ID: <0000013c4e1ea131-b8ab56b9-bfca-44fe-b5da-f030551194c9-000000@email.amazonses.com> 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> <1358468924.23211.69.camel@gandalf.local.home> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Steven Rostedt Cc: LKML , linux-mm , Andrew Morton , Pekka Enberg , Matt Mackall , Thomas Gleixner , RT , Clark Williams , John Kacur , "Luis Claudio R. Goncalves" On Thu, 17 Jan 2013, Steven Rostedt wrote: > 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. Its easiest to just check for the NULL pointer as initally done. The call to __slab_alloc can do what the fastpath does. And the fastpath will verify that the c->page pointer was not changed. -- 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