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>

1 files changed, 6 insertions, 10 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 1782beed2fa7..79893123325c 100644
--- 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;