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From:   Chen Yu <yu.c.chen@intel.com>
To:     Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>
Cc:     Phil Auld <pauld@redhat.com>,
        Biju Das <biju.das.jz@bp.renesas.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        linux-kernel@vger.kernel.org, Tim Chen <tim.c.chen@intel.com>,
        Chen Yu <yu.chen.surf@gmail.com>, Chen Yu <yu.c.chen@intel.com>
Subject: [PATCH] sched/fair: Use printk_deferred instead of printk in pick_eevdf()
Date:   Tue, 10 Oct 2023 11:25:41 +0800
Message-Id: <20231010032541.339606-1-yu.c.chen@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

When no eligible entity is found in pick_eevdf(), it has to pick
the entity with smallest vruntime. This indicates a potential issue
and scheduler will print this error.

However this printk could introduce possible circular locking issue
because when the code path reaches here with the rq lock held, the
printk could trigger further scheduling which loops back to the
scheduler.

Use printk_deferred() to defer the console write from current context
to the irq work in the next tick.

Fixes: 147f3efaa241 ("sched/fair: Implement an EEVDF-like scheduling policy")
Suggested-by: Phil Auld <pauld@redhat.com>
Reported-by: Biju Das <biju.das.jz@bp.renesas.com>
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 061a30a8925a..70f38e54b6ce 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -973,7 +973,7 @@ static struct sched_entity *pick_eevdf(struct cfs_rq *cfs_rq)
 	if (!se) {
 		struct sched_entity *left = __pick_first_entity(cfs_rq);
 		if (left) {
-			pr_err("EEVDF scheduling fail, picking leftmost\n");
+			printk_deferred(KERN_ERR "EEVDF scheduling fail, picking leftmost\n");
 			return left;
 		}
 	}
-- 
2.25.1