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cpumask: remove cpumask allocation from idle_balance

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Impact: fix circular locking

Steven reports a circular locking from alloc_cpumask_var doing
a wakeup. We get rid of this using the tried-and-true technique
of using a per-cpu cpumask_var_t rather than doing an alloc
every time.

Simpler and more robust than a rare, implicit allocation within
an atomic codepath.

Reported-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
LKML-Reference: <alpine.DEB.2.00.0903181729360.31583@gandalf.stny.rr.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Rusty Russell 2009-03-19 15:22:20 +10:30 committed by Ingo Molnar
parent c38da5692e
commit df7c8e845e
1 changed files with 18 additions and 17 deletions
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35
kernel/sched.c
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@ -3448,19 +3448,23 @@ find_busiest_queue(struct sched_group *group, enum cpu_idle_type idle,
*/
#define MAX_PINNED_INTERVAL 512
/* Working cpumask for load_balance and load_balance_newidle. */
static DEFINE_PER_CPU(cpumask_var_t, load_balance_tmpmask);
/*
* Check this_cpu to ensure it is balanced within domain. Attempt to move
* tasks if there is an imbalance.
*/
static int load_balance(int this_cpu, struct rq *this_rq,
struct sched_domain *sd, enum cpu_idle_type idle,
int *balance, struct cpumask *cpus)
int *balance)
{
int ld_moved, all_pinned = 0, active_balance = 0, sd_idle = 0;
struct sched_group *group;
unsigned long imbalance;
struct rq *busiest;
unsigned long flags;
struct cpumask *cpus = __get_cpu_var(load_balance_tmpmask);
cpumask_setall(cpus);
@ -3615,8 +3619,7 @@ static int load_balance(int this_cpu, struct rq *this_rq,
* this_rq is locked.
*/
static int
load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd,
struct cpumask *cpus)
load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd)
{
struct sched_group *group;
struct rq *busiest = NULL;
@ -3624,6 +3627,7 @@ load_balance_newidle(int this_cpu, struct rq *this_rq, struct sched_domain *sd,
int ld_moved = 0;
int sd_idle = 0;
int all_pinned = 0;
struct cpumask *cpus = __get_cpu_var(load_balance_tmpmask);
cpumask_setall(cpus);
@ -3764,10 +3768,6 @@ static void idle_balance(int this_cpu, struct rq *this_rq)
struct sched_domain *sd;
int pulled_task = 0;
unsigned long next_balance = jiffies + HZ;
cpumask_var_t tmpmask;
if (!alloc_cpumask_var(&tmpmask, GFP_ATOMIC))
return;
for_each_domain(this_cpu, sd) {
unsigned long interval;
@ -3778,7 +3778,7 @@ static void idle_balance(int this_cpu, struct rq *this_rq)
if (sd->flags & SD_BALANCE_NEWIDLE)
/* If we've pulled tasks over stop searching: */
pulled_task = load_balance_newidle(this_cpu, this_rq,
sd, tmpmask);
sd);
interval = msecs_to_jiffies(sd->balance_interval);
if (time_after(next_balance, sd->last_balance + interval))
@ -3793,7 +3793,6 @@ static void idle_balance(int this_cpu, struct rq *this_rq)
*/
this_rq->next_balance = next_balance;
}
free_cpumask_var(tmpmask);
}
/*
@ -3943,11 +3942,6 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
unsigned long next_balance = jiffies + 60*HZ;
int update_next_balance = 0;
int need_serialize;
cpumask_var_t tmp;
/* Fails alloc? Rebalancing probably not a priority right now. */
if (!alloc_cpumask_var(&tmp, GFP_ATOMIC))
return;
for_each_domain(cpu, sd) {
if (!(sd->flags & SD_LOAD_BALANCE))
@ -3972,7 +3966,7 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
}
if (time_after_eq(jiffies, sd->last_balance + interval)) {
if (load_balance(cpu, rq, sd, idle, &balance, tmp)) {
if (load_balance(cpu, rq, sd, idle, &balance)) {
/*
* We've pulled tasks over so either we're no
* longer idle, or one of our SMT siblings is
@ -4006,8 +4000,6 @@ static void rebalance_domains(int cpu, enum cpu_idle_type idle)
*/
if (likely(update_next_balance))
rq->next_balance = next_balance;
free_cpumask_var(tmp);
}
/*
@ -8303,6 +8295,9 @@ void __init sched_init(void)
#endif
#ifdef CONFIG_USER_SCHED
alloc_size *= 2;
#endif
#ifdef CONFIG_CPUMASK_OFFSTACK
alloc_size *= num_possible_cpus() * cpumask_size();
#endif
/*
* As sched_init() is called before page_alloc is setup,
@ -8341,6 +8336,12 @@ void __init sched_init(void)
ptr += nr_cpu_ids * sizeof(void **);
#endif /* CONFIG_USER_SCHED */
#endif /* CONFIG_RT_GROUP_SCHED */
#ifdef CONFIG_CPUMASK_OFFSTACK
for_each_possible_cpu(i) {
per_cpu(load_balance_tmpmask, i) = (void *)ptr;
ptr += cpumask_size();
}
#endif /* CONFIG_CPUMASK_OFFSTACK */
}
#ifdef CONFIG_SMP