From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id 9E2201F3D56; Tue, 25 Aug 2026 05:19:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=13.77.154.182 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787635143; cv=none; b=A25gYvUtU8hgUjMqN/7qsuhC88XZYyJSQW6oJaST8wKFItuGFLtZdsohc+Ih/nV3fhE09bd3iDnwbcf8KLigVkrbSXdftaJ+Pi6Oe8qfczDFZvsxw7kUfqBW7diTVrFOdkavGi2VozDICmIxWrivLtBNRbaFlYJQEFwmjWdqDt8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787635143; c=relaxed/simple; bh=8DgmtUn3Fzm43q42Nhr/eVs7RwM+IyYFXBcQi5BHGRQ=; h=From:To:Subject:Date:Message-ID:MIME-Version; b=fhsAiuDrr7oQiqbvDGGWL3dFP99tumDS+J9rBk0hoKoGMX0pzilzaBDgTgNFITPqA1ScAJI2SnGzIZBhhiHW4aiCpkK5B2Tep0w0kBNVbKnWxK32UzeSz5KQ7jvv9rkS8Gc5ieKVTzV8P7so6faCHbTMFPPzquRrhFFRzhVW9bY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com; spf=pass smtp.mailfrom=linux.microsoft.com; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b=hp/57e7r; arc=none smtp.client-ip=13.77.154.182 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.microsoft.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linux.microsoft.com header.i=@linux.microsoft.com header.b="hp/57e7r" Received: from sahil.mshome.net (unknown [4.213.232.22]) by linux.microsoft.com (Postfix) with ESMTPSA id C429E20B7166; Mon, 24 Aug 2026 22:18:26 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com C429E20B7166 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1787635110; bh=9BxmoeNKcrVz0BFb+VjuMoWpZF9NlmX83HbgkVBiwLo=; h=From:To:Subject:Date:From; b=hp/57e7raKygHgltk2moRgCuREsWghbZtRTUF/8W6GZv63FdgfP3apiV1P8By1NVd 6OklWSrVc0XiBrwqV3ory43WUdxTsBwgNDZUA4+/tc/xdHIXKwymXUoOFXzyGVAzub D9DnjfdbOegiUhlSI9X3byQSQlnC/5PExSHReiBs= From: Sahil Chandna To: kys@microsoft.com, haiyangz@microsoft.com, wei.liu@kernel.org, decui@microsoft.com, longli@microsoft.com, lpieralisi@kernel.org, kwilczynski@kernel.org, mani@kernel.org, robh@kernel.org, bhelgaas@google.com, linux-hyperv@vger.kernel.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] PCI: hv: Warn when wait_for_response() waits indefinitely Date: Mon, 24 Aug 2026 22:17:00 -0700 Message-ID: <20260825051850.2438816-1-sahilchandna@linux.microsoft.com> X-Mailer: git-send-email 2.53.0 Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit A guest can wait indefinitely in wait_for_response() for the host to send either a rescind message or a packet completion. If the host does not send either, the guest can remain blocked with no diagnostic indicating a reason. This was observed during a guest kernel upgrade in which the host-side application handling the PCI channel faulted, causing the guest to never receive the completion request. Add a periodic warning in wait_for_response() when the wait exceeds a timeout so that such a hang is visible in the guest's kernel log and can be correlated with host-side state. Suggested-by: Hamza Mahfooz Signed-off-by: Sahil Chandna --- This was sent earlier upstream [1] [1] https://lore.kernel.org/linux-hyperv/20260612174010.2598695-1-hamzamahfooz@linux.microsoft.com/ --- drivers/pci/controller/pci-hyperv.c | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index cfc8fa403dad..c4fba0039164 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -1040,11 +1040,18 @@ static void put_pcichild(struct hv_pci_dev *hpdev) /* * There is no good way to get notified from vmbus_onoffer_rescind(), - * so let's use polling here, since this is not a hot path. + * so let's use polling here, since this is not a hot path. If + * wait_for_response() has been polling for PCI_RESPONSE_HANG_TIMEOUT_SEC + * without either a rescind or completion, add a periodic warning. */ +#define PCI_RESPONSE_HANG_TIMEOUT_SEC 300 + static int wait_for_response(struct hv_device *hdev, struct completion *comp) { + unsigned long delay = secs_to_jiffies(PCI_RESPONSE_HANG_TIMEOUT_SEC); + u64 timeout = get_jiffies_64() + delay; + while (true) { if (hdev->channel->rescind) { dev_warn_once(&hdev->device, "The device is gone.\n"); @@ -1053,6 +1060,11 @@ static int wait_for_response(struct hv_device *hdev, if (wait_for_completion_timeout(comp, HZ / 10)) break; + + if (time_after64(get_jiffies_64(), timeout)) { + dev_warn(&hdev->device, "PCI stuck waiting for response.\n"); + timeout = get_jiffies_64() + delay; + } } return 0; -- 2.53.0