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 8185B47F2DD; Sat, 12 Sep 2026 13:44:40 +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=1789220681; cv=none; b=tdAX1To4NxKzHYlPmnGgRccx1LS/1iywo0tmC8zI62OpCd+nhz8lO3ZNhJ0dCwtXU0d3VJlzNZa33WGDmgPUww20iVGNZa1a4uBolw1w5/N5EjT6dBTCRpifEeOV4L8mc8r3aCJOI9cLz6IMkglSLBwwb8/oASH4+K5fO9V8Dzs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789220681; c=relaxed/simple; bh=oL8lD2Mei5HtQXa+Qcnk0424H0W0xwrmWzu2g+2fZEU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=gB37Fma7Hx/o21JcL1WgqX4NI5S1Me6CfFJCdTBWor6/WL0X2rSKyQR/OprpHh479dU10c0rCXnHWvqaqwoelFX79d/xKiAZfn9M29XeujFZF1SO584aSHtDF2HoObk8NGedIG/VvuybZsAz1Xwub5oLHDyG2l5JJii3NV7KW1Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=zsFqw7sx; 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="zsFqw7sx" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2AC321F000FF; Sat, 12 Sep 2026 13:44:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789220680; bh=S7dFo3L3/7A/lvPQTKI/yO7RMRUYQeTQOUbUMFv9bC0=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=zsFqw7sxFIvm8BCQtJyqZfRkvECfQ4qhlDSxlCC7OvSqh0g6M+P9eVmwcqrDydNJ8 K72QYzzPDA8AM5FJZqaWxM99R0NnkcO5C5o3097REYDPMGecFTsdi7QkRk3M0AgC1z kBUge2ohXxv9vXUFoVm/wksvgeJhgtqVJYDqPsUI= 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 6.6 0227/1424] PCI/proc: Avoid spurious runtime PM wakeup on config space accesses Date: Sat, 12 Sep 2026 08:44:19 +0200 Message-ID: <20260912065612.368843453@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065607.279695368@linuxfoundation.org> References: <20260912065607.279695368@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 6.6-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) @@ -121,6 +124,9 @@ static ssize_t proc_bus_pci_write(struct if (ret) return ret; + if (!nbytes) + return 0; + if (pos >= size) return 0; if (nbytes >= size)