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 871F3340298; Sat, 12 Sep 2026 18:16:20 +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=1789236981; cv=none; b=kzX+JyLGCk8exwe+uSToLLR1BRhVYVgV0WYwbeXybA5Zko1mzRmsgaftayScL8W54Wl9Mu1VnRVkZBy6H1Hub5iZuxSb5zLJwks+5t5MdIFWGHq5u9F6E4JmZDU3tx4MKak/2dbJfEXLayStpu/WN5VC2cXeQ7/g3JdOkd+zRdA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1789236981; c=relaxed/simple; bh=TbYih27lI2A7FvnB6GyqBbsNDjJ1LANgKY1o7bXOcGU=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=TKDaq+srA9AEKnW9h+qCYEfedgBjK3i876sb/EldeGgvvSMyC7Y5TYnUDkOc722XUdeudDpoOwz8umD4ObO0ZcphNkr4z+AALUHLoDj1NVBAT+ehKMI9jCQ/DLOnBZxrrUgXCLrL5LC7J++M2FKetuwDOlzhdUk+cChLEO9rHcY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=yCWmL4Fm; 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="yCWmL4Fm" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2EB9D1F000FF; Sat, 12 Sep 2026 18:16:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1789236980; bh=rukjS7EiBTsUX0R13pCv0HBjl4jQGExzZFDIs5yV1Oc=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=yCWmL4FmcocACqLw0Eg1GQmKyhajPuFwhijkzUQ0CIbbKcRtT6e6G86K1uZ4ZvgRK NWlEbt64ZonZm7jUZ4K1r54uZu1uvzTab6BsYZc+2RUEzOgRFF/YryJtKZ9fHO1m6e 5dhXiAdUGWvKMk+242NYRtMZo7zgMaBZa6OB05V8= 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 5.15 164/935] PCI/proc: Avoid spurious runtime PM wakeup on config space accesses Date: Sat, 12 Sep 2026 08:53:14 +0200 Message-ID: <20260912065530.580801187@linuxfoundation.org> X-Mailer: git-send-email 2.55.0 In-Reply-To: <20260912065526.833703348@linuxfoundation.org> References: <20260912065526.833703348@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 5.15-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) @@ -123,6 +126,9 @@ static ssize_t proc_bus_pci_write(struct if (ret) return ret; + if (!nbytes) + return 0; + if (pos >= size) return 0; if (nbytes >= size)