[tip:sched/urgent] sched: Reassign prev and switch_count when reacquire_kernel_lock() fail

From: tip-bot for Yong Zhang
Date: Thu Jan 21 2010 - 08:52:39 EST

Commit-ID: 6d558c3ac9b6508d26fd5cadccce51fc9d726b1c
Gitweb: http://git.kernel.org/tip/6d558c3ac9b6508d26fd5cadccce51fc9d726b1c
Author: Yong Zhang <yong.zhang0@xxxxxxxxx>
AuthorDate: Mon, 11 Jan 2010 14:21:25 +0800
Committer: Ingo Molnar <mingo@xxxxxxx>
CommitDate: Thu, 21 Jan 2010 13:39:04 +0100

sched: Reassign prev and switch_count when reacquire_kernel_lock() fail

Assume A->B schedule is processing, if B have acquired BKL before and it
need reschedule this time. Then on B's context, it will go to
need_resched_nonpreemptible for reschedule. But at this time, prev and
switch_count are related to A. It's wrong and will lead to incorrect
scheduler statistics.

Signed-off-by: Yong Zhang <yong.zhang0@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
LKML-Reference: <2674af741001102238w7b0ddcadref00d345e2181d11@xxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
kernel/sched.c | 5 ++++-
1 files changed, 4 insertions(+), 1 deletions(-)

diff --git a/kernel/sched.c b/kernel/sched.c
index c535cc4..4508fe7 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5530,8 +5530,11 @@ need_resched_nonpreemptible:


- if (unlikely(reacquire_kernel_lock(current) < 0))
+ if (unlikely(reacquire_kernel_lock(current) < 0)) {
+ prev = rq->curr;
+ switch_count = &prev->nivcsw;
goto need_resched_nonpreemptible;
+ }

if (need_resched())
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