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SubjectRE: [PATCH] Fix the race between smp_call_function and CPU booting
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Date
On Tue, 2012-03-20 at 00:22 +0000, Liu, Chuansheng wrote:
> Thanks to give some time to have a look.
>
Does the below on top of current tip/master work?
>
---
include/linux/cpuset.h | 6 +---
kernel/cpuset.c | 20 +++------------
kernel/sched/core.c | 62 +++++++++++++++++++++++++++++++++++------------
3 files changed, 52 insertions(+), 36 deletions(-)

diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index e9eaec5..e0ffaf0 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -22,7 +22,7 @@ extern int cpuset_init(void);
extern void cpuset_init_smp(void);
extern void cpuset_update_active_cpus(void);
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
-extern int cpuset_cpus_allowed_fallback(struct task_struct *p);
+extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
#define cpuset_current_mems_allowed (current->mems_allowed)
void cpuset_init_current_mems_allowed(void);
@@ -144,10 +144,8 @@ static inline void cpuset_cpus_allowed(struct task_struct *p,
cpumask_copy(mask, cpu_possible_mask);
}

-static inline int cpuset_cpus_allowed_fallback(struct task_struct *p)
+static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)
{
- do_set_cpus_allowed(p, cpu_possible_mask);
- return cpumask_any(cpu_active_mask);
}

static inline nodemask_t cpuset_mems_allowed(struct task_struct *p)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index a09ac2b..c9837b7 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -2195,7 +2195,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
mutex_unlock(&callback_mutex);
}

-int cpuset_cpus_allowed_fallback(struct task_struct *tsk)
+void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
{
const struct cpuset *cs;
int cpu;
@@ -2219,22 +2219,10 @@ int cpuset_cpus_allowed_fallback(struct task_struct *tsk)
* changes in tsk_cs()->cpus_allowed. Otherwise we can temporary
* set any mask even if it is not right from task_cs() pov,
* the pending set_cpus_allowed_ptr() will fix things.
+ *
+ * select_fallback_rq() will fix things ups and set cpu_possible_mask
+ * if required.
*/
-
- cpu = cpumask_any_and(&tsk->cpus_allowed, cpu_active_mask);
- if (cpu >= nr_cpu_ids) {
- /*
- * Either tsk->cpus_allowed is wrong (see above) or it
- * is actually empty. The latter case is only possible
- * if we are racing with remove_tasks_in_empty_cpuset().
- * Like above we can temporary set any mask and rely on
- * set_cpus_allowed_ptr() as synchronization point.
- */
- do_set_cpus_allowed(tsk, cpu_possible_mask);
- cpu = cpumask_any(cpu_active_mask);
- }
-
- return cpu;
}

void cpuset_init_current_mems_allowed(void)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e37c9af..04d3f7f 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -1263,29 +1263,59 @@ EXPORT_SYMBOL_GPL(kick_process);
*/
static int select_fallback_rq(int cpu, struct task_struct *p)
{
- int dest_cpu;
const struct cpumask *nodemask = cpumask_of_node(cpu_to_node(cpu));
+ enum { cpuset, possible, fail } state = cpuset;
+ int dest_cpu;

/* Look for allowed, online CPU in same node. */
- for_each_cpu_and(dest_cpu, nodemask, cpu_active_mask)
+ for_each_cpu_mask(dest_cpu, *nodemask) {
+ if (!cpu_online(dest_cpu))
+ continue;
+ if (!cpu_active(dest_cpu))
+ continue;
if (cpumask_test_cpu(dest_cpu, tsk_cpus_allowed(p)))
return dest_cpu;
+ }

- /* Any allowed, online CPU? */
- dest_cpu = cpumask_any_and(tsk_cpus_allowed(p), cpu_active_mask);
- if (dest_cpu < nr_cpu_ids)
- return dest_cpu;
+ for (;;) {
+ /* Any allowed, online CPU? */
+ for_each_cpu_mask(dest_cpu, *tsk_cpus_allowed(p)) {
+ if (!cpu_online(dest_cpu))
+ continue;
+ if (!cpu_active(dest_cpu))
+ continue;
+ goto out;
+ }

- /* No more Mr. Nice Guy. */
- dest_cpu = cpuset_cpus_allowed_fallback(p);
- /*
- * Don't tell them about moving exiting tasks or
- * kernel threads (both mm NULL), since they never
- * leave kernel.
- */
- if (p->mm && printk_ratelimit()) {
- printk_sched("process %d (%s) no longer affine to cpu%d\n",
- task_pid_nr(p), p->comm, cpu);
+ switch (state) {
+ case cpuset:
+ /* No more Mr. Nice Guy. */
+ cpuset_cpus_allowed_fallback(p);
+ state = possible;
+ break;
+
+ case possible:
+ do_set_cpus_allowed(p, cpu_possible_mask);
+ state = fail;
+ break;
+
+ case fail:
+ BUG();
+ break;
+ }
+ }
+
+out:
+ if (state != cpuset) {
+ /*
+ * Don't tell them about moving exiting tasks or
+ * kernel threads (both mm NULL), since they never
+ * leave kernel.
+ */
+ if (p->mm && printk_ratelimit()) {
+ printk_sched("process %d (%s) no longer affine to cpu%d\n",
+ task_pid_nr(p), p->comm, cpu);
+ }
}

return dest_cpu;


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