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 C14D62E1C63; Tue, 6 Jan 2026 17:46:53 +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=1767721613; cv=none; b=j46WjlqIHblTrVfAFG2VWBq/ibnGgGlLbLJkJWuhruWqlCNJlwtOnSf9lbeBCFj1AvgCbdo9c6MoieqIipqrF8GGT4WSiLjofGbOH/3esBcvCQO6y0wf7cSxDZ/vSss3kFKnOq7/2UltMwkuMjSVFhxLXkd7YpO9iD5B4p0/b58= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1767721613; c=relaxed/simple; bh=RTJHEFa2TrQ93qSzMdELueRlF8bYmL6PtbL1trPGOWw=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=Wey9PfyJfkLzbz+xU71BGJs5jDgpJcxmQ1o3eNarVjAx5LeIQK3+AOtd8neBLjLclKDiItJx7bfnSvmdS0SUmf+3G4ri9yFVBWSBNNKhC79DtkHJ9X1GO9BKW3tT68tY9tCOVzEr4WMK78GP1ZP1FgWRgZ8algJ0gRnV9FHY4T8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=kZmIBK6Q; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="kZmIBK6Q" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 307F5C116C6; Tue, 6 Jan 2026 17:46:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1767721613; bh=RTJHEFa2TrQ93qSzMdELueRlF8bYmL6PtbL1trPGOWw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=kZmIBK6QnmvFnukRFCRsnLAfKlQujbbSIKw3hTbjeAli4AVCpY+DXtqdZT69YNBkT kx/slU+jI5GNTJBahoykL9JzVjwNwIWkRgvp1AhRPX2aLgJR99v9gRle9xi0UyRLRe im4krv2sRj9/Uhc4Hj28zgZrNUBmKZ61yAE6EWUs= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Zqiang , Andrea Righi , Tejun Heo , Sasha Levin Subject: [PATCH 6.18 006/312] sched_ext: Fix incorrect sched_class settings for per-cpu migration tasks Date: Tue, 6 Jan 2026 18:01:20 +0100 Message-ID: <20260106170548.071330598@linuxfoundation.org> X-Mailer: git-send-email 2.52.0 In-Reply-To: <20260106170547.832845344@linuxfoundation.org> References: <20260106170547.832845344@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ 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 Signed-off-by: Greg Kroah-Hartman --- kernel/sched/ext.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) --- a/kernel/sched/ext.c +++ b/kernel/sched/ext.c @@ -210,6 +210,14 @@ static struct scx_dispatch_q *find_user_ return rhashtable_lookup_fast(&sch->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 @@ -3994,8 +4002,7 @@ static void scx_disable_workfn(struct kt 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) @@ -4779,8 +4786,7 @@ static int scx_enable(struct sched_ext_o 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))