sched: Use rcu in sched_get/set_affinity()

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>

diff --git a/kernel/sched.c b/kernel/sched.c
index 1782bee..7989312 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6516,22 +6516,18 @@ long sched_setaffinity(pid_t pid, const struct cpumask *in_mask)
        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;
@@ -6617,7 +6613,7 @@ long sched_getaffinity(pid_t pid, struct cpumask *mask)
        int retval;
 
        get_online_cpus();
-       read_lock(&tasklist_lock);
+       rcu_read_lock();
 
        retval = -ESRCH;
        p = find_process_by_pid(pid);
@@ -6633,7 +6629,7 @@ long sched_getaffinity(pid_t pid, struct cpumask *mask)
        task_rq_unlock(rq, &flags);
 
 out_unlock:
-       read_unlock(&tasklist_lock);
+       rcu_read_unlock();
        put_online_cpus();
 
        return retval;