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Subject[074/123] sched: Use rcu in sched_get/set_affinity()
From: Thomas Gleixner <tglx@linutronix.de>

commit 23f5d142519621b16cf2b378cf8adf4dcf01a616 upstream

tasklist_lock is held read locked to protect the
find_task_by_vpid() call and to prevent the task going away.
sched_setaffinity acquires a task struct ref and drops tasklist
lock right away. The access to the cpus_allowed mask is
protected by rq->lock.

rcu_read_lock() provides the same protection here.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
LKML-Reference: <20091209100706.789059966@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
---
kernel/sched.c | 16 ++++++----------
1 file changed, 6 insertions(+), 10 deletions(-)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6563,22 +6563,18 @@ long sched_setaffinity(pid_t pid, const
int retval;

get_online_cpus();
- read_lock(&tasklist_lock);
+ rcu_read_lock();

p = find_process_by_pid(pid);
if (!p) {
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
put_online_cpus();
return -ESRCH;
}

- /*
- * It is not safe to call set_cpus_allowed with the
- * tasklist_lock held. We will bump the task_struct's
- * usage count and then drop tasklist_lock.
- */
+ /* Prevent p going away */
get_task_struct(p);
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();

if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) {
retval = -ENOMEM;
@@ -6664,7 +6660,7 @@ long sched_getaffinity(pid_t pid, struct
int retval;

get_online_cpus();
- read_lock(&tasklist_lock);
+ rcu_read_lock();

retval = -ESRCH;
p = find_process_by_pid(pid);
@@ -6680,7 +6676,7 @@ long sched_getaffinity(pid_t pid, struct
task_rq_unlock(rq, &flags);

out_unlock:
- read_unlock(&tasklist_lock);
+ rcu_read_unlock();
put_online_cpus();

return retval;



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