From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 176B710F1 for ; Mon, 29 Dec 2025 19:39:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767037163; cv=none; b=GmovUnb+bNxHsmb+Mc00VTx59+bbUYjTtD8dVwHtHmZRXWctosvoPWm2IjAQPotoX/y/NYhd2YE5Dhj2+g+bYrnIOt5OVT+OrX0YgWg9T56hmDjHawLM896nidt4MrUxda+3GIPeiuc22czp8nCEcVWMOddJEbwFc5rEEy3ZZFk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767037163; c=relaxed/simple; bh=6+ae7Ag/xahvj5V3qktvrU5r24sDpXEQAxBOunWKK/w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=s5qRzXkPyYFS1+UdVbrgIrbh3FtKgPSUSp2Zs8ca1YYrCB/cMNi6hoPhP3igRAPBxIYY9x1oAR+dNiJCgnnMDzLfbafR/THnZTHURULTp+PukJ9TiIT1q0FZvK9WRopgFZYSCkt11sYzyijXuWbJrdgXM2F7/aLwmlwDGXwfI6Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=gVNoZg06; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="gVNoZg06" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 539A2C4CEF7; Mon, 29 Dec 2025 19:39:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1767037162; bh=6+ae7Ag/xahvj5V3qktvrU5r24sDpXEQAxBOunWKK/w=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=gVNoZg06smYBZY/XAof2Q6AwEt+yHrB3VMVfJZhhddZ97mIt/24pXt23VSx3rbIpb HBMauSA/5J7kJCxFV7/RxYfMSabvLeAe6PhG8knd0mdKfyr21xq7twjpT2lhGEaGSw DP5aRJEI4LOFF6i4g5Ng8fE4fREAidsOLRHEjf4mmip7cCSQtMC78Vuck/uDcwb1NO 7Hzhdq2vPapVKoz5Ge+E030WenPpuPrlRIIu+1dcFAX9loXUZIy5M4SjfJPH1PoVGk i5q1uGw+s2cXYfglgCv9ktK1MK83yYDIYI44OtuKoK0zB1TrZuRc46aSqNKk5wB+2f TpttZcHevSo4Q== From: Sasha Levin To: stable@vger.kernel.org Cc: Zqiang , Andrea Righi , Tejun Heo , Sasha Levin Subject: [PATCH 6.12.y] sched_ext: Fix incorrect sched_class settings for per-cpu migration tasks Date: Mon, 29 Dec 2025 14:39:20 -0500 Message-ID: <20251229193920.1643627-1-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <2025122909-remover-casino-d84a@gregkh> References: <2025122909-remover-casino-d84a@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Zqiang [ Upstream commit 1dd6c84f1c544e552848a8968599220bd464e338 ] When loading the ebpf scheduler, the tasks in the scx_tasks list will be traversed and invoke __setscheduler_class() to get new sched_class. however, this would also incorrectly set the per-cpu migration task's->sched_class to rt_sched_class, even after unload, the per-cpu migration task's->sched_class remains sched_rt_class. The log for this issue is as follows: ./scx_rustland --stats 1 [ 199.245639][ T630] sched_ext: "rustland" does not implement cgroup cpu.weight [ 199.269213][ T630] sched_ext: BPF scheduler "rustland" enabled 04:25:09 [INFO] RustLand scheduler attached bpftrace -e 'iter:task /strcontains(ctx->task->comm, "migration")/ { printf("%s:%d->%pS\n", ctx->task->comm, ctx->task->pid, ctx->task->sched_class); }' Attaching 1 probe... migration/0:24->rt_sched_class+0x0/0xe0 migration/1:27->rt_sched_class+0x0/0xe0 migration/2:33->rt_sched_class+0x0/0xe0 migration/3:39->rt_sched_class+0x0/0xe0 migration/4:45->rt_sched_class+0x0/0xe0 migration/5:52->rt_sched_class+0x0/0xe0 migration/6:58->rt_sched_class+0x0/0xe0 migration/7:64->rt_sched_class+0x0/0xe0 sched_ext: BPF scheduler "rustland" disabled (unregistered from user space) EXIT: unregistered from user space 04:25:21 [INFO] Unregister RustLand scheduler bpftrace -e 'iter:task /strcontains(ctx->task->comm, "migration")/ { printf("%s:%d->%pS\n", ctx->task->comm, ctx->task->pid, ctx->task->sched_class); }' Attaching 1 probe... migration/0:24->rt_sched_class+0x0/0xe0 migration/1:27->rt_sched_class+0x0/0xe0 migration/2:33->rt_sched_class+0x0/0xe0 migration/3:39->rt_sched_class+0x0/0xe0 migration/4:45->rt_sched_class+0x0/0xe0 migration/5:52->rt_sched_class+0x0/0xe0 migration/6:58->rt_sched_class+0x0/0xe0 migration/7:64->rt_sched_class+0x0/0xe0 This commit therefore generate a new scx_setscheduler_class() and add check for stop_sched_class to replace __setscheduler_class(). Fixes: f0e1a0643a59 ("sched_ext: Implement BPF extensible scheduler class") Cc: stable@vger.kernel.org # v6.12+ Signed-off-by: Zqiang Reviewed-by: Andrea Righi Signed-off-by: Tejun Heo [ Adjust context ] Signed-off-by: Sasha Levin --- kernel/sched/ext.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c index ad1d438b3085..614275e4b05c 100644 --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -1057,6 +1057,14 @@ static struct scx_dispatch_q *find_user_dsq(u64 dsq_id) return rhashtable_lookup_fast(&dsq_hash, &dsq_id, dsq_hash_params); } +static const struct sched_class *scx_setscheduler_class(struct task_struct *p) +{ + if (p->sched_class == &stop_sched_class) + return &stop_sched_class; + + return __setscheduler_class(p->policy, p->prio); +} + /* * scx_kf_mask enforcement. Some kfuncs can only be called from specific SCX * ops. When invoking SCX ops, SCX_CALL_OP[_RET]() should be used to indicate @@ -4653,8 +4661,7 @@ static void scx_ops_disable_workfn(struct kthread_work *work) scx_task_iter_start(&sti); while ((p = scx_task_iter_next_locked(&sti))) { const struct sched_class *old_class = p->sched_class; - const struct sched_class *new_class = - __setscheduler_class(p->policy, p->prio); + const struct sched_class *new_class = scx_setscheduler_class(p); struct sched_enq_and_set_ctx ctx; if (old_class != new_class && p->se.sched_delayed) @@ -5368,8 +5375,7 @@ static int scx_ops_enable(struct sched_ext_ops *ops, struct bpf_link *link) scx_task_iter_start(&sti); while ((p = scx_task_iter_next_locked(&sti))) { const struct sched_class *old_class = p->sched_class; - const struct sched_class *new_class = - __setscheduler_class(p->policy, p->prio); + const struct sched_class *new_class = scx_setscheduler_class(p); struct sched_enq_and_set_ctx ctx; if (!tryget_task_struct(p)) -- 2.51.0