From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 82F1B223328; Thu, 28 May 2026 20:30:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780000255; cv=none; b=gE4XDqybpIuhr0xQi69FXe+vXqdUukTpZsppSAYM5XWzk7r+gUVQlRToSNfzJPZd+RfbVoChzx/hLvhGgpBVqiREwVb5jK+gaib9VOPcX12RYdurNnwVnJF4vmgjs80hPTuyZd0v3fet9jfLse4w8ycBmd6r7B/Qk1pRke7DL18= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780000255; c=relaxed/simple; bh=/Ir/0y8UEOtPzS7iA39NjedKtIqvQYDGDWWq3bVynYo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=dr9kRclVwHmJ0BljE5omyWIScS3wWDl9aB1CIrN0II+7MDTACrKhN7md1dLb5anUDMpdcTQhmTNAI718YIXsh54enYhdP70eKrL6piAltfnB+/zXhbKCN7cq9dVW4aNVN7EmKg+OWlh1r46FWvk1ZxYXhJWy952DstV5dhY9JK0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=lxfF9q01; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="lxfF9q01" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E17CA1F000E9; Thu, 28 May 2026 20:30:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1780000254; bh=djIJBSZUXYabq6hObHfh5l3eB26tiG2CenoN1xGTQWw=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=lxfF9q01nV/DWotsWKz3w+CR/QOGWa5MuTmbZObwQnxuPMvP6XtlxBlr7E/0xhZzE dVieiMkDNZiyXA9G7kIJsKMcLdr88Nf82eGqv2okSvM/X1RixJl+f02K4XUzf6AZnl 1RkMjFcONoLF5NnyYsfUFnZWunkiBUvvf3hEKc90= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Cunlong Li , Tejun Heo , Sasha Levin Subject: [PATCH 6.18 350/377] cgroup: rstat: relax NMI guard after switch to try_cmpxchg Date: Thu, 28 May 2026 21:49:48 +0200 Message-ID: <20260528194648.561803667@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260528194638.371537336@linuxfoundation.org> References: <20260528194638.371537336@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: Cunlong Li [ Upstream commit 22572dbcd3486e6c4dced877125bbf50e4e24edf ] Commit 36df6e3dbd7e ("cgroup: make css_rstat_updated nmi safe") used this_cpu_cmpxchg() for the lockless insertion, and therefore required both ARCH_HAVE_NMI_SAFE_CMPXCHG and ARCH_HAS_NMI_SAFE_THIS_CPU_OPS in the NMI guard: on archs without the latter, this_cpu_cmpxchg() falls back to "local_irq_save() + plain cmpxchg", and local_irq_save() cannot mask NMIs. Commit 3309b63a2281 ("cgroup: rstat: use LOCK CMPXCHG in css_rstat_updated") later replaced this_cpu_cmpxchg() with plain try_cmpxchg() to fix cross-CPU lockless-list corruption, but left the NMI guard untouched. After that switch, css_rstat_updated() no longer performs any this_cpu_*() RMW operations and only relies on the arch having NMI-safe cmpxchg, so ARCH_HAS_NMI_SAFE_THIS_CPU_OPS is no longer required in the guard. Relax the guard accordingly so that archs which have HAVE_NMI and ARCH_HAVE_NMI_SAFE_CMPXCHG but not ARCH_HAS_NMI_SAFE_THIS_CPU_OPS (e.g. sparc, powerpc on PPC64/BOOK3S) can benefit from the existing CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC path. Without this, the css is never queued in NMI on those archs, and the atomics staged by account_{slab,kmem}_nmi_safe() are not drained by flush_nmi_stats(). Fixes: 3309b63a2281 ("cgroup: rstat: use LOCK CMPXCHG in css_rstat_updated") Signed-off-by: Cunlong Li Signed-off-by: Tejun Heo Signed-off-by: Sasha Levin --- kernel/cgroup/rstat.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/kernel/cgroup/rstat.c b/kernel/cgroup/rstat.c index ed60ba119c687..de816a43db9f0 100644 --- a/kernel/cgroup/rstat.c +++ b/kernel/cgroup/rstat.c @@ -81,11 +81,10 @@ void __css_rstat_updated(struct cgroup_subsys_state *css, int cpu) lockdep_assert_preemption_disabled(); /* - * For archs withnot nmi safe cmpxchg or percpu ops support, ignore - * the requests from nmi context. + * The lockless insertion below relies on NMI-safe cmpxchg; + * bail out in NMI on archs that don't provide it. */ - if ((!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) || - !IS_ENABLED(CONFIG_ARCH_HAS_NMI_SAFE_THIS_CPU_OPS)) && in_nmi()) + if (!IS_ENABLED(CONFIG_ARCH_HAVE_NMI_SAFE_CMPXCHG) && in_nmi()) return; rstatc = css_rstat_cpu(css, cpu); -- 2.53.0