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SubjectRe: [PATCH 2.6.16-mm1 1/2] sched_domain: handle kmalloc failure
Srivatsa Vaddagiri <vatsa@in.ibm.com> wrote:
>
> 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.
>

This is rather ugly, sorry.

>
>
> 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;

So if the kmalloc failed we'll try to limp along without load balancing?

I think it would be better to free any thus-far allocated memory and to
fail the whole thing.

Returning void from build_sched_domains was wrong.

build_sched_domains() should be static and __cpuinit, btw.

-
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