linux-kernel - [004/121] sched: Fix the broken sched_rr_get

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Message-ID: <lsq.1378608721.203000298@decadent.org.uk>
Date:	Sun, 08 Sep 2013 03:52:01 +0100
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org, "Paul Turner" <pjt@...gle.com>,
	"Thomas Gleixner" <tglx@...utronix.de>,
	"Steven Rostedt" <rostedt@...dmis.org>,
	"Peter Zijlstra" <peterz@...radead.org>,
	"Ingo Molnar" <mingo@...nel.org>,
	"Zhu Yanhai" <gaoyang.zyh@...bao.com>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [004/121] sched: Fix the broken sched_rr_get_interval()

3.2.51-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Zhu Yanhai <gaoyang.zyh@...bao.com>

commit a59f4e079d19464eebb9b06513a1d4f55fdae5ba upstream.

The caller of sched_sliced() should pass se.cfs_rq and se as the
arguments, however in sched_rr_get_interval() we gave it
rq.cfs_rq and se, which made the following computation obviously
wrong.

The change was introduced by commit:

  77034937dc45 sched: fix crash in sys_sched_rr_get_interval()

... 5 years ago, while it had been the correct 'cfs_rq_of' before
the commit. The change seems to be irrelevant to the commit
msg, which was to return a 0 timeslice for tasks that are on an
idle runqueue. So I believe that was just a plain typo.

Signed-off-by: Zhu Yanhai <gaoyang.zyh@...bao.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Paul Turner <pjt@...gle.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Link: http://lkml.kernel.org/r/1357621012-15039-1-git-send-email-gaoyang.zyh@taobao.com
[ Since this is an ABI and an old bug, we'll test this via a
  slow upstream route, to hopefully discover any app breakage. ]
Signed-off-by: Ingo Molnar <mingo@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -5033,7 +5033,7 @@ static unsigned int get_rr_interval_fair
 	 * idle runqueue:
 	 */
 	if (rq->cfs.load.weight)
-		rr_interval = NS_TO_JIFFIES(sched_slice(&rq->cfs, se));
+		rr_interval = NS_TO_JIFFIES(sched_slice(cfs_rq_of(se), se));
 
 	return rr_interval;
 }

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