From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763664AbXJRKp3 (ORCPT ); Thu, 18 Oct 2007 06:45:29 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1760971AbXJRKpU (ORCPT ); Thu, 18 Oct 2007 06:45:20 -0400 Received: from netops-testserver-4-out.sgi.com ([192.48.171.29]:56826 "EHLO relay.sgi.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755494AbXJRKpT (ORCPT ); Thu, 18 Oct 2007 06:45:19 -0400 From: Paul Jackson To: Andrew Morton Cc: Dinakar Guniguntala , Cliff Wickman , Paul Menage , linux-kernel@vger.kernel.org, Randy Dunlap , Nick Piggin , David Rientjes , Paul Jackson , Ingo Molnar Date: Thu, 18 Oct 2007 03:45:16 -0700 Message-Id: <20071018104516.9811.903.sendpatchset@jackhammer.engr.sgi.com> Subject: [PATCH] cpuset sched_load_balance sched domain confusion fix Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Paul Jackson Fix a bug in the cpuset code that recalculates dynamic sched domains. For sufficiently complex cpuset configurations, the recalc code could get confused, due to overwriting some state then using the overwritten values as if they still held the previous value. This could result in kernel oops and other random chaos, overwriting memory. The fix stashes the two values of interest, apn and bpn, in separate local variables, to keep them separate from what will be overwritten. Besides the fix, also: 1) this confusion is easy to detect -- in the event that there are or ever come to be any more such bugs, notice when out of bounds and 'continue' past it, resulting in overly simplified sched domain setups, rather than oops or memory trashing, and 2) in that case, print something out with a few clues, the first ten times this happens on a boot, so that someone might notice someday and chase the problem down. Signed-off-by: Paul Jackson --- This is a needed fix for the *-mm patch: cpuset-sched_load_balance-flag.patch kernel/cpuset.c | 21 ++++++++++++++++++--- 1 file changed, 18 insertions(+), 3 deletions(-) --- 2.6.23-mm1.orig/kernel/cpuset.c 2007-10-17 18:56:09.814604327 -0700 +++ 2.6.23-mm1/kernel/cpuset.c 2007-10-18 01:56:23.863274785 -0700 @@ -631,16 +631,18 @@ restart: /* Find the best partition (set of sched domains) */ for (i = 0; i < csn; i++) { struct cpuset *a = csa[i]; + int apn = a->pn; for (j = 0; j < csn; j++) { struct cpuset *b = csa[j]; + int bpn = b->pn; - if (a->pn != b->pn && cpusets_overlap(a, b)) { + if (apn != bpn && cpusets_overlap(a, b)) { for (k = 0; k < csn; k++) { struct cpuset *c = csa[k]; - if (c->pn == b->pn) - c->pn = a->pn; + if (c->pn == bpn) + c->pn = apn; } ndoms--; /* one less element */ goto restart; @@ -660,6 +662,19 @@ restart: if (apn >= 0) { cpumask_t *dp = doms + nslot; + if (nslot == ndoms) { + static int warnings = 10; + if (warnings) { + printk(KERN_WARNING + "rebuild_sched_domains confused:" + " nslot %d, ndoms %d, csn %d, i %d," + " apn %d\n", + nslot, ndoms, csn, i, apn); + warnings--; + } + continue; + } + cpus_clear(*dp); for (j = i; j < csn; j++) { struct cpuset *b = csa[j]; -- I won't rest till it's the best ... Programmer, Linux Scalability Paul Jackson 1.650.933.1373