linux-kernel - Re: bad patch in sched.c

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Message-Id: <200901102234.37460.rusty@rustcorp.com.au>
Date:	Sat, 10 Jan 2009 22:34:36 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Mike Travis <travis@....com>
Cc:	Ingo Molnar <mingo@...e.hu>, Jes Sorensen <jes@....com>,
	Jack Steiner <steiner@....com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: bad patch in sched.c

On Saturday 10 January 2009 05:00:28 Mike Travis wrote:
> 
> It appears that 
> 
> commit 6c99e9ad47d9c082bd096f42fb49e397b05d58a8
> Author: Rusty Russell <rusty@...tcorp.com.au>
> Date:   Tue Nov 25 02:35:04 2008 +1030
> 
>     sched: convert struct sched_group/sched_domain cpumask_ts to variable bitmaps
> 
>     Impact: (future) size reduction for large NR_CPUS.
> 
>     We move the 'cpumask' member of sched_group to the end, so when we
>     kmalloc it we can do a minimal allocation: saves space for small
>     nr_cpu_ids but big CONFIG_NR_CPUS.  Similar trick for 'span' in
>     sched_domain.
> 
>     This isn't quite as good as converting to a cpumask_var_t, as some
>     sched_groups are actually static, but it's safer: we don't have to
>     figure out where to call alloc_cpumask_var/free_cpumask_var.
> 
>     Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
>     Signed-off-by: Ingo Molnar <mingo@...e.hu>
> 
> 
> causes a panic in ia64 with NR_CPUS=1024.

Thanks, that focussed me on the right place.  Does this fix it?

cpumask: fix CONFIG_NUMA=y sched.c

struct sched_domain is now a dangling structure; where we really want
static ones, we need to use static_sched_domain.

(As the FIXME in this file says, cpumask_var_t would be better, but
this code is hairy enough without trying to add initialization code to
the right places).

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>

diff --git a/kernel/sched.c b/kernel/sched.c
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7282,10 +7282,10 @@ cpu_to_phys_group(int cpu, const struct 
  * groups, so roll our own. Now each node has its own list of groups which
  * gets dynamically allocated.
  */
-static DEFINE_PER_CPU(struct sched_domain, node_domains);
+static DEFINE_PER_CPU(struct static_sched_domain, node_domains);
 static struct sched_group ***sched_group_nodes_bycpu;
 
-static DEFINE_PER_CPU(struct sched_domain, allnodes_domains);
+static DEFINE_PER_CPU(struct static_sched_domain, allnodes_domains);
 static DEFINE_PER_CPU(struct static_sched_group, sched_group_allnodes);
 
 static int cpu_to_allnodes_group(int cpu, const struct cpumask *cpu_map,
@@ -7560,7 +7560,7 @@ static int __build_sched_domains(const s
 #ifdef CONFIG_NUMA
 		if (cpumask_weight(cpu_map) >
 				SD_NODES_PER_DOMAIN*cpumask_weight(nodemask)) {
-			sd = &per_cpu(allnodes_domains, i);
+			sd = &per_cpu(allnodes_domains, i).sg;
 			SD_INIT(sd, ALLNODES);
 			set_domain_attribute(sd, attr);
 			cpumask_copy(sched_domain_span(sd), cpu_map);
@@ -7570,7 +7570,7 @@ static int __build_sched_domains(const s
 		} else
 			p = NULL;
 
-		sd = &per_cpu(node_domains, i);
+		sd = &per_cpu(node_domains, i).sd;
 		SD_INIT(sd, NODE);
 		set_domain_attribute(sd, attr);
 		sched_domain_node_span(cpu_to_node(i), sched_domain_span(sd));
@@ -7688,7 +7688,7 @@ static int __build_sched_domains(const s
 		for_each_cpu(j, nodemask) {
 			struct sched_domain *sd;
 
-			sd = &per_cpu(node_domains, j);
+			sd = &per_cpu(node_domains, j).sd;
 			sd->groups = sg;
 		}
 		sg->__cpu_power = 0;
--
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