linux-kernel - Re: [BUG] i386 2.6.18 cpu_up: attempt to bring up CPU 4 failed : kernel BUG at mm/slab.c:2698!

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Message-Id: <20060922123045.d7258e13.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 22 Sep 2006 12:30:45 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andrew Morton <akpm@...l.org>
Cc:	kmannth@...ibm.com, linux-kernel@...r.kernel.org,
	clameter@...r.sgi.com
Subject: Re: [BUG] i386 2.6.18 cpu_up: attempt to bring up CPU 4 failed :
 kernel BUG at mm/slab.c:2698!

On Thu, 21 Sep 2006 20:08:06 -0700
Andrew Morton <akpm@...l.org> wrote:

> But why did the kmalloc() fail?
> 
> 
from this:

==
#define NOTIFY_DONE             0x0000          /* Don't care */
#define NOTIFY_OK               0x0001          /* Suits me */
#define NOTIFY_STOP_MASK        0x8000          /* Don't call further */
#define NOTIFY_BAD              (NOTIFY_STOP_MASK|0x0002)
==

I gues someone returns NOTIFY_BAD before pageset_cpuup_callback() is called.
When CPU_UP_CANCELED comes, pageset_cpuup_callback() can't know zone_pcp()
is kmalloced or not. Is this ugly ?

-Kame

Before kfree(), we should check zone_pcp() is not boot_pageset[].

Signed-Off-By KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>

Index: linux-2.6.18/mm/page_alloc.c
===================================================================
--- linux-2.6.18.orig/mm/page_alloc.c	2006-09-20 12:42:06.000000000 +0900
+++ linux-2.6.18/mm/page_alloc.c	2006-09-22 12:22:03.000000000 +0900
@@ -1844,9 +1844,11 @@
 
 	for_each_zone(zone) {
 		struct per_cpu_pageset *pset = zone_pcp(zone, cpu);
-
-		zone_pcp(zone, cpu) = NULL;
-		kfree(pset);
+		/* When canceled, zone_pcp still points to boot_pageset[] */
+		if (zone_pcp(zone, cpu) != &boot_pageset[cpu]) {
+			zone_pcp(zone, cpu) = NULL;
+			kfree(pset);
+		}
 	}
 }
 

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