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Subject[PATCH] Fix sched_domain sysctl registration again
commit  029190c515f15f512ac85de8fc686d4dbd0ae731 (cpuset
sched_load_balance flag) was not tested SCHED_DEBUG enabled as
committed as it dereferences NULL when used and it reordered
the sysctl registration to cause it to never show any domains
or their tunables.


1) restore arch_init_sched_domains ordering
we can't walk the domains before we build them

presently we register cpus with empty directories (no domain
directories or files).

2) make unregister_sched_domain_sysctl do nothing when already unregistered
detach_destroy_domains is now called one set of cpus at a time
unregister_syctl dereferences NULL if called with a null.

While the the function would always dereference null if called
twice, in the previous code it was always called once and then
was followed a register. So only the hidden bug of the
sysctl_root_table not being allocated followed by an attempt to
free it would have shown the error.

3) always call unregister and register in partition_sched_domains
The code is "smart" about unregistering only needed domains.
Since we aren't guaranteed any calls to unregister, always
unregister. Without calling register on the way out we
will not have a table or any sysctl tree.

4) warn if register is called without unregistering
The previous table memory is lost, leaving pointers to the
later freed memory in sysctl and leaking the memory of the

Signed-off-by: Milton Miller <>
[resend with From set]
against e8b8c977734193adedf2b0f607d6252c78e86394

Before this patch on a 2-core 4-thread box compiled for SMT and NUMA,
the domains appear empty (there are actually 3 levels per cpu). And as
soon as two domains a null pointer is dereferenced (unreliable in this
case is stack garbage):

bu19a:~# ls -R /proc/sys/kernel/sched_domain/
cpu0 cpu1 cpu2 cpu3





bu19a:~# mkdir /dev/cpuset
bu19a:~# mount -tcpuset cpuset /dev/cpuset/
bu19a:~# cd /dev/cpuset/
bu19a:/dev/cpuset# echo 0 > sched_load_balance
bu19a:/dev/cpuset# mkdir one
bu19a:/dev/cpuset# echo 1 > one/cpus
bu19a:/dev/cpuset# echo 0 > one/sched_load_balance
Unable to handle kernel paging request for data at address 0x00000018
Faulting instruction address: 0xc00000000006b608
NIP: c00000000006b608 LR: c00000000006b604 CTR: 0000000000000000
REGS: c000000018d973f0 TRAP: 0300 Not tainted (2.6.23-bml)
MSR: 9000000000009032 <EE,ME,IR,DR> CR: 28242442 XER: 00000000
DAR: 0000000000000018, DSISR: 0000000040000000
TASK = c00000001912e340[1987] 'bash' THREAD: c000000018d94000 CPU: 2
NIP [c00000000006b608] .unregister_sysctl_table+0x38/0x110
LR [c00000000006b604] .unregister_sysctl_table+0x34/0x110
Call Trace:
[c000000018d97670] [c000000007017270] 0xc000000007017270 (unreliable)
[c000000018d97720] [c000000000058710] .detach_destroy_domains+0x30/0xb0
[c000000018d977b0] [c00000000005cf1c] .partition_sched_domains+0x1bc/0x230
[c000000018d97870] [c00000000009fdc4] .rebuild_sched_domains+0xb4/0x4c0
[c000000018d97970] [c0000000000a02e8] .update_flag+0x118/0x170
[c000000018d97a80] [c0000000000a1768] .cpuset_common_file_write+0x568/0x820
[c000000018d97c00] [c00000000009d95c] .cgroup_file_write+0x7c/0x180
[c000000018d97cf0] [c0000000000e76b8] .vfs_write+0xe8/0x1b0
[c000000018d97d90] [c0000000000e810c] .sys_write+0x4c/0x90
[c000000018d97e30] [c00000000000852c] syscall_exit+0x0/0x40

diff --git a/kernel/sched.c b/kernel/sched.c
index afe76ec..2af50ec 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5463,11 +5463,12 @@ static void register_sched_domain_sysctl(void)
struct ctl_table *entry = sd_alloc_ctl_entry(cpu_num + 1);
char buf[32];

+ WARN_ON(sd_ctl_dir[0].child);
+ sd_ctl_dir[0].child = entry;
if (entry == NULL)

- sd_ctl_dir[0].child = entry;
for_each_online_cpu(i) {
snprintf(buf, 32, "cpu%d", i);
entry->procname = kstrdup(buf, GFP_KERNEL);
@@ -5475,14 +5476,19 @@ static void register_sched_domain_sysctl(void)
entry->child = sd_alloc_ctl_cpu_table(i);
+ WARN_ON(sd_sysctl_header);
sd_sysctl_header = register_sysctl_table(sd_ctl_root);

+/* may be called multiple times per register */
static void unregister_sched_domain_sysctl(void)
- unregister_sysctl_table(sd_sysctl_header);
+ if (sd_sysctl_header)
+ unregister_sysctl_table(sd_sysctl_header);
sd_sysctl_header = NULL;
- sd_free_ctl_entry(&sd_ctl_dir[0].child);
+ if (sd_ctl_dir[0].child)
+ sd_free_ctl_entry(&sd_ctl_dir[0].child);
static void register_sched_domain_sysctl(void)
@@ -6426,13 +6432,17 @@ static cpumask_t fallback_doms;
static int arch_init_sched_domains(const cpumask_t *cpu_map)
+ int err;
ndoms_cur = 1;
doms_cur = kmalloc(sizeof(cpumask_t), GFP_KERNEL);
if (!doms_cur)
doms_cur = &fallback_doms;
cpus_andnot(*doms_cur, *cpu_map, cpu_isolated_map);
+ err = build_sched_domains(doms_cur);
- return build_sched_domains(doms_cur);
+ return err;

static void arch_destroy_sched_domains(const cpumask_t *cpu_map)
@@ -6481,6 +6491,9 @@ void partition_sched_domains(int ndoms_new, cpumask_t *doms_new)
int i, j;

+ /* always unregister in case we don't destroy any domains */
+ unregister_sched_domain_sysctl();
if (doms_new == NULL) {
ndoms_new = 1;
doms_new = &fallback_doms;
@@ -6516,6 +6529,8 @@ match2:
doms_cur = doms_new;
ndoms_cur = ndoms_new;
+ register_sched_domain_sysctl();

#if defined(CONFIG_SCHED_MC) || defined(CONFIG_SCHED_SMT)
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