[tip:sched/urgent] sched: Remove unnecessary RCU exclusion

tip-bot for Peter Zijlstra
2009-12-09T09:59:21Z

Commit-ID: fb58bac5c75bfff8bbf7d02071a10a62f32fe28b
Gitweb: http://git.kernel.org/tip/fb58bac5c75bfff8bbf7d02071a10a62f32fe28b
Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
AuthorDate: Tue, 1 Dec 2009 12:21:47 +0100
Committer: Ingo Molnar <mingo@elte.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@suse.de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.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 */