linux-kernel - [tip:sched/urgent] sched: Remove unnecessary RCU exclusion

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Date:	Wed, 9 Dec 2009 09:55:20 GMT
From:	tip-bot for Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, npiggin@...e.de, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	mingo@...e.hu
Subject: [tip:sched/urgent] sched: Remove unnecessary RCU exclusion

Commit-ID:  fb58bac5c75bfff8bbf7d02071a10a62f32fe28b
Gitweb:     http://git.kernel.org/tip/fb58bac5c75bfff8bbf7d02071a10a62f32fe28b
Author:     Peter Zijlstra <a.p.zijlstra@...llo.nl>
AuthorDate: Tue, 1 Dec 2009 12:21:47 +0100
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Wed, 9 Dec 2009 10:03:08 +0100

sched: Remove unnecessary RCU exclusion

As Nick pointed out, and realized by myself when doing:
   sched: Fix balance vs hotplug race
the patch:
   sched: for_each_domain() vs RCU

is wrong, sched_domains are freed after synchronize_sched(), which
means disabling preemption is enough.

Reported-by: Nick Piggin <npiggin@...e.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 kernel/sched_fair.c |    9 ++-------
 1 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index e9f5dae..c163a28 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1403,7 +1403,6 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
 		new_cpu = prev_cpu;
 	}
 
-	rcu_read_lock();
 	for_each_domain(cpu, tmp) {
 		/*
 		 * If power savings logic is enabled for a domain, see if we
@@ -1484,10 +1483,8 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
 			update_shares(tmp);
 	}
 
-	if (affine_sd && wake_affine(affine_sd, p, sync)) {
-		new_cpu = cpu;
-		goto out;
-	}
+	if (affine_sd && wake_affine(affine_sd, p, sync))
+		return cpu;
 
 	while (sd) {
 		int load_idx = sd->forkexec_idx;
@@ -1528,8 +1525,6 @@ static int select_task_rq_fair(struct task_struct *p, int sd_flag, int wake_flag
 		/* while loop will break here if sd == NULL */
 	}
 
-out:
-	rcu_read_unlock();
 	return new_cpu;
 }
 #endif /* CONFIG_SMP */
--
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