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 5BC3E3750D6; Sat, 12 Sep 2026 19:31:33 +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=1789241494; cv=none; b=RUHqVOt2pzfHfLiFTYdYgBZtBZ+BWUWGEpH2I8WYxj8yvXLZCuFLvPmv5NRMEBcEOYKGtGJQ1Z+R3eKiN/sRPFXt8tDGbjDhTQE3r3uNrDhyWQFMnTefEvDAalFiix3Ye4yxzP8jqGvnuCbBS+VIP8z8G6rcKw7TKASEx4NROxo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789241494; c=relaxed/simple; bh=XQZNbV028+5ecNP21hwte6u4/4ymBCkOOE/vYk/K0d4=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=ATfBxrmQjEWqsBQfLe/6Q5wupXbORMmddlkH0fnkNAxSHOrDVQAPMtHPllc5189K/kzHFPAA7oNtGw/WDFLorvAqab/5se8RtSOaLADriWWpDxCcM3x4kg6pkymtT5+kCw2HZXHOljyQLYAkU7+bfuYcdvrWto2aZWeN0huRzjY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=gTRrwU44; 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="gTRrwU44" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 61BD01F000FF; Sat, 12 Sep 2026 19:31:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789241493; bh=uN/scruJb41MnlOqDC3v0wAGTsSamYOVnV15vnv0JIk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=gTRrwU44xOEepW/pVzeAwOf7e8ODvYrTt4So0qz7MMaxhXT2Ne0jiUSQ8XJlf2gkO z+Qi8kT/8mkkQklQcQ0COlmn4NyUwoDKMNjs7TAdfzYIrZc+jKTD5AYeuOd2ak/6T/ YsKk7kpklRkcZnjcVa3qU+XOjX25lrJoSj0lIzpM= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, =?UTF-8?q?Krzysztof=20Wilczy=C5=84ski?= , Bjorn Helgaas Subject: [PATCH 5.10 145/798] PCI/proc: Avoid spurious runtime PM wakeup on config space accesses Date: Sat, 12 Sep 2026 08:56:13 +0200 Message-ID: <20260912065520.313268703@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065516.948645775@linuxfoundation.org> References: <20260912065516.948645775@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 5.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Krzysztof Wilczyński commit 4ff664a81d729b37f2eb65de80a670abfb61c9a0 upstream. Currently, proc_bus_pci_read() and proc_bus_pci_write() do not return early for zero-length configuration space accesses at valid offsets. Such an access invokes pci_config_pm_runtime_get() and pci_config_pm_runtime_put() around transfer blocks that do nothing. This is a problem because pci_config_pm_runtime_get() synchronously resumes the upstream bridge through pm_runtime_get_sync(), and resumes the device itself through pm_runtime_resume() when it is in D3cold, only for the handler to return zero immediately afterwards. Such a spurious wakeup wastes power and adds needless resume latency. The sysfs core already returns early for in-range zero-length binary attribute accesses before pci_read_config() or pci_write_config() is invoked. In contrast, the VFS forwards zero-length requests to the procfs callbacks, where they continue into runtime PM handling. Return early from proc_bus_pci_read() and proc_bus_pci_write() when nbytes is zero, before any runtime PM involvement. The value returned to userspace at these offsets remains zero, so the change is not visible to userspace. Signed-off-by: Krzysztof Wilczyński [bhelgaas: order tags] Signed-off-by: Bjorn Helgaas Cc: stable@vger.kernel.org Link: https://patch.msgid.link/20260729075909.1219906-1-kwilczynski@kernel.org Signed-off-by: Greg Kroah-Hartman --- drivers/pci/proc.c | 6 ++++++ 1 file changed, 6 insertions(+) --- a/drivers/pci/proc.c +++ b/drivers/pci/proc.c @@ -45,6 +45,9 @@ static ssize_t proc_bus_pci_read(struct else size = 64; + if (!nbytes) + return 0; + if (pos >= size) return 0; if (nbytes >= size) @@ -122,6 +125,9 @@ static ssize_t proc_bus_pci_write(struct if (ret) return ret; + if (!nbytes) + return 0; + if (pos >= size) return 0; if (nbytes >= size)