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Subject[PATCH 2.6.16-mm1 1/2] sched_domain: handle kmalloc failure
I think there is a bug in build_sched_domains() when kmalloc fails to
allocate memory for 'sched_group_allnodes'.

Consider the case where build_sched_domains() is being invoked because a
CPUset is being made exclusive. Further lets say user changed cpu_exclusive
property of some CPUset as follow:

echo 1 > cpu_exclusive # (Step a)
echo 0 > cpu_exclusive # (Step b)
echo 1 > cpu_exclusive # (Step c)

Lets say that all memory allocations succeeded during the 1st attempt to
make CPUset exclusive (Step a). Step a would result in the sched domain
heirarchy being initialized for all CPUs in the CPUSet under
consideration. Step b would cause those memory allocations to be freed
up.

Now during Step c, lets say that kmalloc failed to allocate for
'sched_group_allnodes'. When that happens, the code just breaks out of
the 'for' loop. I think that is wrong, as it would cause the previous
assignments (made during Step a) to be retained. This could cause, among
other things, sd->groups to be invalid (for allnodes_domains)?

Patch below (against 2.6.16-mm1) fixes it. I have done some minimal test
of it.

Signed-off-by: Srivatsa Vaddagiri <vatsa@in.ibm.com>



kernel/sched.c | 10 +++++++---
1 files changed, 7 insertions(+), 3 deletions(-)
diff -puN kernel/sched.c~sd_handle_error kernel/sched.c
--- linux-2.6.16-mm1/kernel/sched.c~sd_handle_error 2006-03-25 11:39:07.000000000 +0530
+++ linux-2.6.16-mm1-root/kernel/sched.c 2006-03-25 11:39:59.000000000 +0530
@@ -5965,6 +5965,7 @@ void build_sched_domains(const cpumask_t
{
int i;
#ifdef CONFIG_NUMA
+ int alloc_failed = 0;
struct sched_group **sched_group_nodes = NULL;
struct sched_group *sched_group_allnodes = NULL;

@@ -5993,7 +5994,7 @@ void build_sched_domains(const cpumask_t
#ifdef CONFIG_NUMA
if (cpus_weight(*cpu_map)
> SD_NODES_PER_DOMAIN*cpus_weight(nodemask)) {
- if (!sched_group_allnodes) {
+ if (!sched_group_allnodes && !alloc_failed) {
sched_group_allnodes
= kmalloc(sizeof(struct sched_group)
* MAX_NUMNODES,
@@ -6001,7 +6002,7 @@ void build_sched_domains(const cpumask_t
if (!sched_group_allnodes) {
printk(KERN_WARNING
"Can not alloc allnodes sched group\n");
- break;
+ alloc_failed = 1;
}
sched_group_allnodes_bycpu[i]
= sched_group_allnodes;
@@ -6010,7 +6011,10 @@ void build_sched_domains(const cpumask_t
*sd = SD_ALLNODES_INIT;
sd->span = *cpu_map;
group = cpu_to_allnodes_group(i);
- sd->groups = &sched_group_allnodes[group];
+ sd->groups = sched_group_allnodes ?
+ &sched_group_allnodes[group] : NULL;
+ if (!sd->groups)
+ sd->flags = 0; /* No load balancing */
p = sd;
} else
p = NULL;
_

--
Regards,
vatsa
-
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