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sched: Prevent race conditions where upmigrate_min_nice changes 

When upmigrate_min_nice is changed dec_nr_big_small_task() can trigger
BUG_ON(rq->nr_big_tasks < 0).  This happens when there is a task which was
considered as non-big task due to its nice > upmigrate_min_nice and later
upmigrate_min_nice is changed to higher value so the task becomes big task.
In this case runqueue still has nr_big_tasks = 0 incorrectly with current
implementation.  Consequently next scheduler tick sees a big task to
schedule and try to decrease nr_big_tasks which is already 0.

Introduce sched_upmigrate_min_nice which is updated atomically and re-count
the number of big and small tasks to fix BUG_ON() triggering.

Change-Id: I6f5fc62ed22bbe5c52ec71613082a6e64f406e58
Signed-off-by: Joonwoo Park <joonwoop@codeaurora.org>
This commit is contained in:
Joonwoo Park 2014-12-16 10:20:40 -08:00
parent f6e9e18ec2
commit 2cec55a2e2
2 changed files with 38 additions and 16 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

52
kernel/sched/fair.c
View File

@ -1324,6 +1324,7 @@ unsigned int __read_mostly sysctl_sched_downmigrate_pct = 60;
* Tasks whose nice value is > sysctl_sched_upmigrate_min_nice are never
* considered as "big" tasks.
*/
static int __read_mostly sched_upmigrate_min_nice = 15;
int __read_mostly sysctl_sched_upmigrate_min_nice = 15;
/*
@ -1374,6 +1375,8 @@ void set_hmp_defaults(void)
sched_init_task_load_windows =
div64_u64((u64)sysctl_sched_init_task_load_pct *
(u64)sched_ravg_window, 100);
sched_upmigrate_min_nice = sysctl_sched_upmigrate_min_nice;
}
u32 sched_get_init_task_load(struct task_struct *p)
@ -1470,7 +1473,7 @@ static inline int is_big_task(struct task_struct *p)
int nice = TASK_NICE(p);
/* Todo: Provide cgroup-based control as well? */
if (nice > sysctl_sched_upmigrate_min_nice)
if (nice > sched_upmigrate_min_nice)
return 0;
load = scale_load_to_cpu(load, task_cpu(p));
@ -1658,7 +1661,7 @@ static int task_will_fit(struct task_struct *p, int cpu)
return 1;
} else {
/* Todo: Provide cgroup-based control as well? */
if (nice > sysctl_sched_upmigrate_min_nice)
if (nice > sched_upmigrate_min_nice)
return 1;
load = scale_load_to_cpu(task_load(p), cpu);
@ -2197,11 +2200,16 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write,
int ret;
unsigned int *data = (unsigned int *)table->data;
unsigned int old_val = *data;
int update_min_nice = 0;
ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
if (ret || !write || !sched_enable_hmp)
return ret;
if (write && (old_val == *data))
return 0;
if (data == &sysctl_sched_min_runtime) {
sched_min_runtime = ((u64) sysctl_sched_min_runtime) * 1000;
return 0;
@ -2212,6 +2220,23 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write,
return -EINVAL;
}
if (data == (unsigned int *)&sysctl_sched_upmigrate_min_nice)
update_min_nice = 1;
if (update_min_nice) {
if ((*(int *)data) < -20 || (*(int *)data) > 19) {
*data = old_val;
return -EINVAL;
}
} else {
/* all tunables other than min_nice are in percentage */
if (sysctl_sched_downmigrate_pct >
sysctl_sched_upmigrate_pct || *data > 100) {
*data = old_val;
return -EINVAL;
}
}
/*
* Big/Small task tunable change will need to re-classify tasks on
* runqueue as big and small and set their counters appropriately.
@ -2220,20 +2245,18 @@ int sched_hmp_proc_update_handler(struct ctl_table *table, int write,
* includes taking runqueue lock of all online cpus and re-initiatizing
* their big/small counter values based on changed criteria.
*/
if ((*data != old_val) &&
(data == &sysctl_sched_upmigrate_pct ||
data == &sysctl_sched_small_task_pct)) {
get_online_cpus();
pre_big_small_task_count_change(cpu_online_mask);
if ((data == &sysctl_sched_upmigrate_pct ||
data == &sysctl_sched_small_task_pct || update_min_nice)) {
get_online_cpus();
pre_big_small_task_count_change(cpu_online_mask);
}
set_hmp_defaults();
if ((*data != old_val) &&
(data == &sysctl_sched_upmigrate_pct ||
data == &sysctl_sched_small_task_pct)) {
post_big_small_task_count_change(cpu_online_mask);
put_online_cpus();
if ((data == &sysctl_sched_upmigrate_pct ||
data == &sysctl_sched_small_task_pct || update_min_nice)) {
post_big_small_task_count_change(cpu_online_mask);
put_online_cpus();
}
return 0;
@ -2346,9 +2369,8 @@ static inline int migration_needed(struct rq *rq, struct task_struct *p)
return 0;
/* Todo: cgroup-based control? */
if (nice > sysctl_sched_upmigrate_min_nice &&
rq->capacity > min_capacity)
return MOVE_TO_LITTLE_CPU;
if (nice > sched_upmigrate_min_nice && rq->capacity > min_capacity)
return MOVE_TO_LITTLE_CPU;
if (!task_will_fit(p, cpu_of(rq)))
return MOVE_TO_BIG_CPU;

2
kernel/sysctl.c
View File

@ -414,7 +414,7 @@ static struct ctl_table kern_table[] = {
.data = &sysctl_sched_upmigrate_min_nice,
.maxlen = sizeof(unsigned int),
.mode = 0644,
.proc_handler = proc_dointvec,
.proc_handler = sched_hmp_proc_update_handler,
},
{
.procname = "sched_prefer_idle",