linux-kernel - [tip:sched/urgent] sched: Use rcu in sched_get/set

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Date:	Mon, 14 Dec 2009 16:31:19 GMT
From:	tip-bot for Thomas Gleixner <tglx@...utronix.de>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...hat.com,
	peterz@...radead.org, tglx@...utronix.de, mingo@...e.hu
Subject: [tip:sched/urgent] sched: Use rcu in sched_get/set_affinity()

Commit-ID:  23f5d142519621b16cf2b378cf8adf4dcf01a616
Gitweb:     http://git.kernel.org/tip/23f5d142519621b16cf2b378cf8adf4dcf01a616
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Wed, 9 Dec 2009 10:15:01 +0000
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Mon, 14 Dec 2009 17:11:35 +0100

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@...utronix.de>
Cc: Peter Zijlstra <peterz@...radead.org>
LKML-Reference: <20091209100706.789059966@...utronix.de>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched.c |   16 ++++++----------
 1 files changed, 6 insertions(+), 10 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index 1782bee..7989312 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;
--
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