sched: Use rcu in sched_get/set_affinity() (23f5d142) · Commits · 戴 / test

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>

kernel/sched.c

+6 −10

Original line number	Diff line number	Diff line
		@@ -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;

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