linux-kernel - Bug in SCHED_IDLE interaction with group scheduling?

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Message-ID: <alpine.DEB.1.00.0907101649570.29914@kitami.corp.google.com>
Date:	Fri, 10 Jul 2009 17:05:16 -0700 (PDT)
From:	Paul Turner <pjt@...gle.com>
To:	peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Bug in SCHED_IDLE interaction with group scheduling?

Hi Peter,

It seems like there's an assumption in the sched_idle policy check in 
place_entity that the sched_entity we are looking at belongs to a task?

- Paul

--

sched: bug in SCHED_IDLE interaction with group scheduling

One of the isolation modifications for SCHED_IDLE is the unitization of sleeper
credit.  However the check for this assumes that the sched_entity we're placing
always belongs to a task.

This is potentially not true with group scheduling and leaves us rummaging
randomly when we try to pull the policy.

Signed-off-by: Paul Turner <pjt@...gle.com>
---
 kernel/sched_fair.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index ba7fd6e..7c248dc 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -687,7 +687,8 @@ place_entity(struct cfs_rq *cfs_rq, struct sched_entity *se, int initial)
 			 * all of which have the same weight.
 			 */
 			if (sched_feat(NORMALIZED_SLEEPER) &&
-					task_of(se)->policy != SCHED_IDLE)
+					(!entity_is_task(se) ||
+					 task_of(se)->policy != SCHED_IDLE))
 				thresh = calc_delta_fair(thresh, se);

 			vruntime -= thresh;
-- 
1.5.4.3

--
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