From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (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 5CFB7326930; Fri, 29 May 2026 09:18:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780046284; cv=none; b=hwXybccTWJMrCs5hVR9myVWtsIyhWQg87OAnijnfz9qJK+mvpI1k5oVl6Ok40hqwF8yMlNZHzdjcNgZdKDrQ7KpPWhNn1psFEc/8M4DWYXkYNMQQhhJefQqdmEiQvMeT+pM2hm4I0roTIzT+zUj1t0IYGYQJkrUDhDnFz1I3PJI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780046284; c=relaxed/simple; bh=UKXf1wPA+hemjuXg7ukP/htrv1MeVbTufACnpt4UqB8=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=MBTKpPcBB43DqZasR76OuW7y7uul8TeyUO4tZERc0DoVPoDHNycZ0pS7vjCqx2mhhoGhZMq1KpeuJYSOsF/pXgp/vn2HWxhFRu8vFMQAHmSeTbQDmux2Tw8jT20ro4Gyb9H0Im7YhIHB2IQoGRQYPKkCxcZO+ZBBIcjFXy2EFh4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=S4d5H3qa; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="S4d5H3qa" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=3X+h87zVQbiADPCPME4wwho65wKw5nknhCHOBBKB/ZY=; b=S4d5H3qarX01z/0rutOkGmmtgH SmafBLNzWSuRikquCnziG8k6GrnvLHPFhPRuOT3QvQS2TPy297K/UTdkimkO+hxne3sSLUIZTmNAq 9c/6l3GZ8/JCT+v6HV6Dlub5gF9Em85WhV44v4LajUdu9tII/JQ/jgZI65gHLSM86P5h7L9LcKWv5 5r2xmaLIMNNV81Rc5+dlEfgCzl2AMuzm/uByCPPZv3+cyzS3wvEIgWb+vsoIbvY1CSCSyKgZSiCAI Q/RlCxJFIptG3MUxVHbnkVtyL8t2sdTzIMxejtZ4mGhP0o8T1F4YAvIaLiBOi0i/aCqzCwwhA6pe6 8G2je/rA==; Received: from 2001-1c00-8d85-4b00-266e-96ff-fe07-7dcc.cable.dynamic.v6.ziggo.nl ([2001:1c00:8d85:4b00:266e:96ff:fe07:7dcc] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.99.1 #2 (Red Hat Linux)) id 1wStLn-00000000t4y-2wo2; Fri, 29 May 2026 09:17:56 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id D4C5E301CEB; Fri, 29 May 2026 11:17:54 +0200 (CEST) Date: Fri, 29 May 2026 11:17:54 +0200 From: Peter Zijlstra To: Shrikanth Hegde Cc: maddy@linux.ibm.com, linuxppc-dev@lists.ozlabs.org, mingo@kernel.org, christophe.leroy@csgroup.eu, linux-kernel@vger.kernel.org, venkat88@linux.ibm.com, yu.c.chen@intel.com, tim.c.chen@linux.intel.com, kprateek.nayak@amd.com, srikar@linux.ibm.com, riteshh@linux.ibm.com, stable@vger.kernel.org, "Ritesh Harjani (IBM)" Subject: Re: [PATCH] sched/topology: Provide arch_llc_mask for cache aware scheduling Message-ID: <20260529091754.GO343181@noisy.programming.kicks-ass.net> References: <20260529075712.1181039-1-sshegde@linux.ibm.com> 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: <20260529075712.1181039-1-sshegde@linux.ibm.com> On Fri, May 29, 2026 at 01:27:12PM +0530, Shrikanth Hegde wrote: > Venkat Reported a boot kernel panic next-20260522. Git bisect pointed to > b5ea300a17e3 ("sched/cache: Make LLC id continuous") > > Stacktrace points to llc_mask being null. > > NIP [c000000000e58504] _find_first_bit+0x44/0x130 > LR [c000000000e58500] _find_first_bit+0x40/0x130 > Call Trace: > build_sched_domains+0xad8/0xe50 > sched_init_smp+0xa8/0x164 > kernel_init_freeable+0x250/0x370 > ret_from_kernel_user_thread+0x14/0x1c > > On powerpc, cpu_coregroup_mask is available only when the underlying > hardware support coregroup. In shared LPAR, QEMU guest or power9 etc > coregroup isn't supported. In such cases llc_mask was being referenced > when it was null leading to panic. > > On powerpc, LLC is at SMT core level. So assumption that coregroup(MC) > domain point to LLC is wrong. Provide a way for archs to say where its > LLC is if it not at MC domain. > > Based on tip/master at 5c89783224e9 ("Merge branch into tip/master: 'x86/tdx'") > Cc: stable@vger.kernel.org This seems unwarranted, the patch breaking stuff is in tip:sched/core. > Fixes: b5ea300a17e3 ("sched/cache: Make LLC id continuous") > Reported-by: Venkat Rao Bagalkote > Closes: https://lore.kernel.org/all/51154de7-3700-4cb4-82f2-1b3a8fa427f7@linux.ibm.com/ > Reviewed-by: Chen Yu > Tested-by: Venkat Rao Bagalkote > Tested-by: Ritesh Harjani (IBM) > Co-developed-by: Chen, Yu C > Signed-off-by: Shrikanth Hegde Thanks all! I'll stick this in tip:sched/core to go along with the patches that broke stuff.