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

Andrew Morton
2006-09-22T03:43:11Z

On Fri, 22 Sep 2006 12:30:45 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Thu, 21 Sep 2006 20:08:06 -0700
> Andrew Morton <akpm@osdl.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@jp.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);
> + }
> }
> }
>

No, that's OK as it is now. The above code is numa-only, in which case
zone_pcp(zone, cpu) is known to be kmalloced. These functions won't even
compile on !NUMA because in that case, zone_pcp() isn't an lvalue.

OBCodingStyleNit: could we pleeeeeze not go and use macros as lvalues like
this? It looks just too weird. Simply do zone_pcp(zone, cpu) and
set_zone_pcp(zone, cpu, val).