This is a note to let you know that I've just added the patch titled
sched: Guarantee new group-entities always have weight
to the 3.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
sched-guarantee-new-group-entities-always-have-weight.patch
and it can be found in the queue-3.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 0ac9b1c21874d2490331233b3242085f8151e166 Mon Sep 17 00:00:00 2001
From: Paul Turner <pjt@xxxxxxxxxx>
Date: Wed, 16 Oct 2013 11:16:27 -0700
Subject: sched: Guarantee new group-entities always have weight
From: Paul Turner <pjt@xxxxxxxxxx>
commit 0ac9b1c21874d2490331233b3242085f8151e166 upstream.
Currently, group entity load-weights are initialized to zero. This
admits some races with respect to the first time they are re-weighted in
earlty use. ( Let g[x] denote the se for "g" on cpu "x". )
Suppose that we have root->a and that a enters a throttled state,
immediately followed by a[0]->t1 (the only task running on cpu[0])
blocking:
put_prev_task(group_cfs_rq(a[0]), t1)
put_prev_entity(..., t1)
check_cfs_rq_runtime(group_cfs_rq(a[0]))
throttle_cfs_rq(group_cfs_rq(a[0]))
Then, before unthrottling occurs, let a[0]->b[0]->t2 wake for the first
time:
enqueue_task_fair(rq[0], t2)
enqueue_entity(group_cfs_rq(b[0]), t2)
enqueue_entity_load_avg(group_cfs_rq(b[0]), t2)
account_entity_enqueue(group_cfs_ra(b[0]), t2)
update_cfs_shares(group_cfs_rq(b[0]))
< skipped because b is part of a throttled hierarchy >
enqueue_entity(group_cfs_rq(a[0]), b[0])
...
We now have b[0] enqueued, yet group_cfs_rq(a[0])->load.weight == 0
which violates invariants in several code-paths. Eliminate the
possibility of this by initializing group entity weight.
Signed-off-by: Paul Turner <pjt@xxxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20131016181627.22647.47543.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Chris J Arges <chris.j.arges@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/sched/fair.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6240,7 +6240,8 @@ void init_tg_cfs_entry(struct task_group
se->cfs_rq = parent->my_q;
se->my_q = cfs_rq;
- update_load_set(&se->load, 0);
+ /* guarantee group entities always have weight */
+ update_load_set(&se->load, NICE_0_LOAD);
se->parent = parent;
}
Patches currently in stable-queue which might be from pjt@xxxxxxxxxx are
queue-3.12/sched-guarantee-new-group-entities-always-have-weight.patch
queue-3.12/sched-fix-hrtimer_cancel-rq-lock-deadlock.patch
queue-3.12/sched-fix-cfs_bandwidth-misuse-of-hrtimer_expires_remaining.patch
queue-3.12/sched-fix-race-on-toggling-cfs_bandwidth_used.patch
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