linux-kernel - [tip: sched/urgent] sched/eevdf: Fix min

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Message-ID: <169683800306.3135.4450756007825411493.tip-bot2@tip-bot2>
Date:   Mon, 09 Oct 2023 07:53:23 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Marek Szyprowski <m.szyprowski@...sung.com>,
        Biju Das <biju.das.jz@...renesas.com>,
        Mike Galbraith <efault@....de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/urgent] sched/eevdf: Fix min_deadline heap integrity

The following commit has been merged into the sched/urgent branch of tip:

Commit-ID:     8dafa9d0eb1a1550a0f4d462db9354161bc51e0c
Gitweb:        https://git.kernel.org/tip/8dafa9d0eb1a1550a0f4d462db9354161bc51e0c
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Fri, 06 Oct 2023 21:24:45 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Mon, 09 Oct 2023 09:48:32 +02:00

sched/eevdf: Fix min_deadline heap integrity

Marek and Biju reported instances of:

  "EEVDF scheduling fail, picking leftmost"

which Mike correlated with cgroup scheduling and the min_deadline heap
getting corrupted; some trace output confirms:

> And yeah, min_deadline is hosed somehow:
>
>    validate_cfs_rq: --- /
>    __print_se: ffff88845cf48080 w: 1024 ve: -58857638 lag: 870381 vd: -55861854 vmd: -66302085 E (11372/tr)
>    __print_se:   ffff88810d165800 w: 25 ve: -80323686 lag: 22336429 vd: -41496434 vmd: -66302085 E (-1//autogroup-31)
>    __print_se:   ffff888108379000 w: 25 ve: 0 lag: -57987257 vd: 114632828 vmd: 114632828 N (-1//autogroup-33)
>    validate_cfs_rq: min_deadline: -55861854 avg_vruntime: -62278313462 / 1074 = -57987256

Turns out that reweight_entity(), which tries really hard to be fast,
does not do the normal dequeue+update+enqueue pattern but *does* scale
the deadline.

However, it then fails to propagate the updated deadline value up the
heap.

Fixes: 147f3efaa241 ("sched/fair: Implement an EEVDF-like scheduling policy")
Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
Reported-by: Biju Das <biju.das.jz@...renesas.com>
Reported-by: Mike Galbraith <efault@....de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
Tested-by: Biju Das <biju.das.jz@...renesas.com>
Tested-by: Mike Galbraith <efault@....de>
Link: https://lkml.kernel.org/r/20231006192445.GE743@noisy.programming.kicks-ass.net
---
 kernel/sched/fair.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ef7490c..a4b904a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3613,6 +3613,7 @@ static void reweight_entity(struct cfs_rq *cfs_rq, struct sched_entity *se,
 		 */
 		deadline = div_s64(deadline * old_weight, weight);
 		se->deadline = se->vruntime + deadline;
+		min_deadline_cb_propagate(&se->run_node, NULL);
 	}
 
 #ifdef CONFIG_SMP