From: Tejun Heo <tj@kernel.org>
To: Andrea Righi <arighi@nvidia.com>
Cc: David Vernet <void@manifault.com>,
Changwoo Min <changwoo@igalia.com>,
Emil Tsalapatis <emil@etsalapatis.com>,
sched-ext@lists.linux.dev, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/3] sched/core: Avoid requeueing a singleton balance callback
Date: Tue, 20 Oct 2026 08:20:25 -1000 [thread overview]
Message-ID: <61d3176fb616261d1571449114fd9f67@kernel.org> (raw)
In-Reply-To: <20261020084400.845842-2-arighi@nvidia.com>
Hello, Andrea.
On Tue, Oct 20, 2026 at 10:43:19AM +0200, Andrea Righi wrote:
> When the callback is the only list entry, its next pointer is NULL, so
> the existing duplicate check misses it. Queueing it again links it to
> itself and causes the wait to run twice.
The last entry of a longer list has the same problem. Its next is NULL
and it isn't rq->balance_callback, so it can be queued again:
1. A is queued on an empty list. A->next is NULL.
2. B is queued. The list is B -> A.
3. A is queued again. A->next = B and the list becomes A -> B -> A.
do_balance_callbacks() then runs A twice. This doesn't affect
kick_sync_bal_cb, as nothing gets queued between the SNT_REPICK and
SNT_PICK calls.
Thanks.
--
tejun
next prev parent reply other threads:[~2026-10-20 18:20 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-20 8:43 [PATCHSET sched_ext/for-7.4-fixes] sched_ext: Fix proxy execution balance callbacks Andrea Righi
2026-10-20 8:43 ` [PATCH 1/3] sched/core: Avoid requeueing a singleton balance callback Andrea Righi
2026-10-20 17:57 ` Tejun Heo
2026-10-20 18:20 ` Tejun Heo [this message]
2026-10-20 8:43 ` [PATCH 2/3] sched_ext: Use irq_work for deferred actions with proxy execution Andrea Righi
2026-10-20 18:20 ` Tejun Heo
2026-10-20 8:43 ` [PATCH 3/3] sched_ext: Remove the foreign CPU check from the kick_sync wait Andrea Righi
2026-10-20 18:20 ` Tejun Heo
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