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Subject[PATCH] ia64 cpuset + build_sched_domains() mangles structures
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I've already sent this to the maintainers, and this is now being sent to a
larger community audience. I have fixed a problem with the ia64 version of
build_sched_domains(), but a similar fix still needs to be made to the
generic build_sched_domains() in kernel/sched.c.

The "dynamic sched domains" functionality has recently been merged into
2.6.13-rcN that sees the dynamic declaration of a cpu-exclusive (a.k.a.
"isolated") cpuset and rebuilds the CPU Scheduler sched domains and sched
groups to separate away the CPUs in this cpu-exclusive cpuset from the
remainder of the non-isolated CPUs. This allows the non-isolated CPUs to
completely ignore the isolated CPUs when doing load-balancing.

Unfortunately, build_sched_domains() expects that a sched domain will
include all the CPUs of each node in the domain, i.e., that no node will
belong in both an isolated cpuset and a non-isolated cpuset. Declaring
a cpuset that violates this presumption will produce flawed data
structures and will oops the kernel.

To trigger the problem (on a NUMA system with >1 CPUs per node):
cd /dev/cpuset
mkdir newcpuset
cd newcpuset
echo 0 >cpus
echo 0 >mems
echo 1 >cpu_exclusive

I have fixed this shortcoming for ia64 NUMA (with multiple CPUs per node).
A similar shortcoming exists in the generic build_sched_domains() (in
kernel/sched.c) for NUMA, and that needs to be fixed also. The fix involves
dynamically allocating sched_group_nodes[] and sched_group_allnodes[] for
each invocation of build_sched_domains(), rather than using global arrays
for these structures. Care must be taken to remember kmalloc() addresses
so that arch_destroy_sched_domains() can properly kfree() the new dynamic
structures.

This is a patch against 2.6.13-rc6.

Signed-off-by: John Hawkes <hawkes@sgi.com>

Index: linux/arch/ia64/kernel/domain.c
===================================================================
--- linux.orig/arch/ia64/kernel/domain.c 2005-08-19 08:54:00.000000000 -0700
+++ linux/arch/ia64/kernel/domain.c 2005-08-20 07:39:32.000000000 -0700
@@ -120,10 +120,10 @@
* gets dynamically allocated.
*/
static DEFINE_PER_CPU(struct sched_domain, node_domains);
-static struct sched_group *sched_group_nodes[MAX_NUMNODES];
+static struct sched_group **sched_group_nodes_bycpu[NR_CPUS];

static DEFINE_PER_CPU(struct sched_domain, allnodes_domains);
-static struct sched_group sched_group_allnodes[MAX_NUMNODES];
+static struct sched_group *sched_group_allnodes_bycpu[NR_CPUS];

static int cpu_to_allnodes_group(int cpu)
{
@@ -138,6 +138,21 @@
void build_sched_domains(const cpumask_t *cpu_map)
{
int i;
+#ifdef CONFIG_NUMA
+ struct sched_group **sched_group_nodes = NULL;
+ struct sched_group *sched_group_allnodes = NULL;
+
+ /*
+ * Allocate the per-node list of sched groups
+ */
+ sched_group_nodes = kmalloc(sizeof(struct sched_group*)*MAX_NUMNODES,
+ GFP_ATOMIC);
+ if (!sched_group_nodes) {
+ printk(KERN_WARNING "Can not alloc sched group node list\n");
+ return;
+ }
+ sched_group_nodes_bycpu[first_cpu(*cpu_map)] = sched_group_nodes;
+#endif

/*
* Set up domains for cpus specified by the cpu_map.
@@ -150,8 +165,21 @@
cpus_and(nodemask, nodemask, *cpu_map);

#ifdef CONFIG_NUMA
- if (num_online_cpus()
+ if (cpus_weight(*cpu_map)
> SD_NODES_PER_DOMAIN*cpus_weight(nodemask)) {
+ if (!sched_group_allnodes) {
+ sched_group_allnodes
+ = kmalloc(sizeof(struct sched_group)
+ * MAX_NUMNODES,
+ GFP_KERNEL);
+ if (!sched_group_allnodes) {
+ printk(KERN_WARNING
+ "Can not alloc allnodes sched group\n");
+ break;
+ }
+ sched_group_allnodes_bycpu[i]
+ = sched_group_allnodes;
+ }
sd = &per_cpu(allnodes_domains, i);
*sd = SD_ALLNODES_INIT;
sd->span = *cpu_map;
@@ -214,8 +242,9 @@
}

#ifdef CONFIG_NUMA
- init_sched_build_groups(sched_group_allnodes, *cpu_map,
- &cpu_to_allnodes_group);
+ if (sched_group_allnodes)
+ init_sched_build_groups(sched_group_allnodes, *cpu_map,
+ &cpu_to_allnodes_group);

for (i = 0; i < MAX_NUMNODES; i++) {
/* Set up node groups */
@@ -226,8 +255,10 @@
int j;

cpus_and(nodemask, nodemask, *cpu_map);
- if (cpus_empty(nodemask))
+ if (cpus_empty(nodemask)) {
+ sched_group_nodes[i] = NULL;
continue;
+ }

domainspan = sched_domain_node_span(i);
cpus_and(domainspan, domainspan, *cpu_map);
@@ -341,7 +372,7 @@
#endif

/* Attach the domains */
- for_each_online_cpu(i) {
+ for_each_cpu_mask(i, *cpu_map) {
struct sched_domain *sd;
#ifdef CONFIG_SCHED_SMT
sd = &per_cpu(cpu_domains, i);
@@ -372,25 +403,42 @@
{
#ifdef CONFIG_NUMA
int i;
- for (i = 0; i < MAX_NUMNODES; i++) {
- cpumask_t nodemask = node_to_cpumask(i);
- struct sched_group *oldsg, *sg = sched_group_nodes[i];
+ int cpu;

- cpus_and(nodemask, nodemask, *cpu_map);
- if (cpus_empty(nodemask))
- continue;
+ for_each_cpu_mask(cpu, *cpu_map) {
+ struct sched_group *sched_group_allnodes
+ = sched_group_allnodes_bycpu[cpu];
+ struct sched_group **sched_group_nodes
+ = sched_group_nodes_bycpu[cpu];
+
+ if (sched_group_allnodes) {
+ kfree(sched_group_allnodes);
+ sched_group_allnodes_bycpu[cpu] = NULL;
+ }

- if (sg == NULL)
+ if (!sched_group_nodes)
continue;
- sg = sg->next;
+
+ for (i = 0; i < MAX_NUMNODES; i++) {
+ cpumask_t nodemask = node_to_cpumask(i);
+ struct sched_group *oldsg, *sg = sched_group_nodes[i];
+
+ cpus_and(nodemask, nodemask, *cpu_map);
+ if (cpus_empty(nodemask))
+ continue;
+
+ if (sg == NULL)
+ continue;
+ sg = sg->next;
next_sg:
- oldsg = sg;
- sg = sg->next;
- kfree(oldsg);
- if (oldsg != sched_group_nodes[i])
- goto next_sg;
- sched_group_nodes[i] = NULL;
+ oldsg = sg;
+ sg = sg->next;
+ kfree(oldsg);
+ if (oldsg != sched_group_nodes[i])
+ goto next_sg;
+ }
+ kfree(sched_group_nodes);
+ sched_group_nodes_bycpu[cpu] = NULL;
}
#endif
}
-
-
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