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 DE6153D9040 for ; Mon, 9 Mar 2026 15:15:29 +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=1773069329; cv=none; b=A0gZW4uzTvehdRWLiCBRoHNBwrHynTcdZHr6RPPv99FsY0tjVgaa/OM8xJrMAZWPlcObtefQXuXHJsA1f9Tir6cQg2XK1JtV0DrJTOo7eMJIFPi4pqCCaZi3WxpTkQ5zv1N8ggokWV4dtA+7zkLjQQ8nlVDAVoWXSC97rJ7JNxA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773069329; c=relaxed/simple; bh=RSzDCCW5LiM+OcTL0v35NkCPW7E2tVuIs/8aUuxyKUk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=je8n+y7DdzZFCWuis1eZffKu757cRPDNvz1PsDGOEWXJppd7WCTCBNUVmYptzk9IZrZ+wRccRl3dnJwvvTVsKIQ8cmpPY9hUII/j8a8WBEZQECS+3WbZ+4SbQYyLayHQ6afNJNmZZNel/CnfRvkbLMyb/Z6ppL/DuTJ88iQgquo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=igBATUz1; 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="igBATUz1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 181CCC2BC86; Mon, 9 Mar 2026 15:15:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773069329; bh=RSzDCCW5LiM+OcTL0v35NkCPW7E2tVuIs/8aUuxyKUk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=igBATUz1p4W/OURIWYY2D845KZkmIfm+EyflGycp2GLoy2u9sS/aqnTzvR6fCVOM0 927Dq7H3OvS7y0OHbVlCN8nSOL5Xw6ohYXyMew8aydPzZW6kvF/d2VTi3tmrVdp5zS 3pst4Dmj9fRYU0Uq97pmqhurY2E4p0qAx6A3KHII= Date: Mon, 9 Mar 2026 16:15:27 +0100 From: Greg KH To: Nathaniel Filardo Cc: stable@vger.kernel.org Subject: Re: 6.12 build failure for non-SMP systems Message-ID: <2026030904-entering-nuptials-d410@gregkh> References: Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Sat, Feb 21, 2026 at 02:04:49PM -0500, Nathaniel Filardo wrote: > Hi stable@ > > The commit https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e61f636cc31042b717a46f6937a2dfaf21f45c91, > first included in 6.12.64, does not properly guard its new references > to `stop_sched_class` under `CONFIG_SMP`, leading to build failures > like the following, even with the significantly newer 6.12.74 release: > > > linux-armv5tel-unknown-linux-gnueabi> LD .tmp_vmlinux1 > linux-armv5tel-unknown-linux-gnueabi> > /nix/store/cn2gkcaa5kfgzjah31c0qlifv9y4yqg5-armv5tel-unknown-linux-gnueabi-binutils-2.44/bin/armv5tel-unknown-linux-gnueabi-ld: > kernel/sched/build_policy.o: in function `scx_ops_disable_workfn': > > linux-armv5tel-unknown-linux-gnueabi> /build/linux-6.12.74/build/../kernel/sched/ext.c:4746:(.text+0x704c): undefined reference to `stop_sched_class' > > linux-armv5tel-unknown-linux-gnueabi> /nix/store/cn2gkcaa5kfgzjah31c0qlifv9y4yqg5-armv5tel-unknown-linux-gnueabi-binutils-2.44/bin/armv5tel-unknown-linux-gnueabi-ld: kernel/sched/build_policy.o: in function `atomic_set': > > linux-armv5tel-unknown-linux-gnueabi> /build/linux-6.12.74/build/../include/linux/atomic/atomic-instrumented.h:69:(.text+0x11c6c): undefined reference to `stop_sched_class' > > A possible fix is simply to add the requisite guard, thus: > diff --git a/kernel/sched/ext.c.orig b/kernel/sched/ext.c > index 9f03255..9a3e5b2 100644 > --- a/kernel/sched/ext.c.orig > +++ b/kernel/sched/ext.c > @@ -1059,8 +1059,10 @@ static struct scx_dispatch_q *find_user_dsq(u64 dsq_id) > > static const struct sched_class *scx_setscheduler_class(struct task_struct *p) > { > +#ifdef CONFIG_SMP > if (p->sched_class == &stop_sched_class) > return &stop_sched_class; > +#endif > > return __setscheduler_class(p->policy, p->prio); > } > > But it may also be desirable to backport > https://github.com/torvalds/linux/commit/cac5cefbade90ff0bb0b393d301fa3b5234cf056 > from mainline, which removes much of the distinction between UP and > SMP schedulers. That patch doesn't backport cleanly, so can you just submit this as a fixup for now in a format that we can apply it in? thanks, greg k-h