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 85E574BCADC; Tue, 8 Sep 2026 11:30:23 +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=1788867031; cv=none; b=ILRVl2aVEUu2uQuoSIW/6MEM0N55lZSBNkrzYZNzr3l9cYuaYM65/1wMixkca2XP5GRcvh2/6tcqDn3PnCg688jsF3W3IDAroPpGfILRpXIw3nF9co1OpzmUNU/Nz962uF0T5VceZdfSG1Fasng/VHPkO6dKaV/sjkuLympxrOA= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788867031; c=relaxed/simple; bh=Ay8pFY6Von/u+7sbCqK+9uCgDSeE1cuiGZedB8gaMqc=; h=From:To:Subject:Date:Message-ID:MIME-Version; b=nKFQ35m+MkttKZfKnWLkp6Ff44RlYmW7XsB+NjupqZBvbNH1tfgVWu4z8Jph/GKU7CqAb+sKBmnHgiZCtvbQWTz3gSKoak6mHm7RcnJ74ZZ6MZcO+W6rndubKj8txdxq1f74VTeobAbiIzRRxpzEJsOnKWgI+w+wX3cry/0XUu8= 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=G/pw3QcZ; 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="G/pw3QcZ" Received: from sahil.mshome.net (unknown [4.213.232.22]) by linux.microsoft.com (Postfix) with ESMTPSA id E818920B7128; Tue, 8 Sep 2026 04:29:36 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com E818920B7128 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1788866980; bh=uOapS0IgUvTjqexlIhF5LIne+9HLwLBjWTm6WhdXXKw=; h=From:To:Subject:Date:From; b=G/pw3QcZr6XKQQlu90qxqirugKnMbYjT4Vh77i829FiARqVn/9KLa7YkdNNKewi0q 77Qv+aaaRdRafouRl1IhAzwnVRacrp2OjuB+Yhf8TflRBD2EaP1yhOCkkJQCN9Ghzx SX8eWppa1d9VZ1caICCZXRnd+39MZLkN0JWDe+3U= 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, mhklinux@outlook.com Subject: [PATCH v3] PCI: hv: Warn when wait_for_response() waits indefinitely Date: Tue, 8 Sep 2026 04:30:06 -0700 Message-ID: <20260908113009.3005964-1-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 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: Michael Kelley Signed-off-by: Sahil Chandna --- Changes since v2: - Add counter based timeout instead of introducing another timer Link to v2: https://lore.kernel.org/all/20260902115854.2629164-1-sahilchandna@linux.microsoft.com/ Changes since v1: - Removed periodic warning to one time warning in 2 minutes - Include vmbus relid and stuck PCI msg. Link to v1: https://lore.kernel.org/all/20260825051850.2438816-1-sahilchandna@linux.microsoft.com/ drivers/pci/controller/pci-hyperv.c | 46 ++++++++++++++++++++++------- 1 file changed, 36 insertions(+), 10 deletions(-) diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c index 89816a2bd7cd..bd07402c47ed 100644 --- a/drivers/pci/controller/pci-hyperv.c +++ b/drivers/pci/controller/pci-hyperv.c @@ -1040,19 +1040,38 @@ 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 2 minutes + * without either a rescind or completion, add a warning. */ +#define PCI_RESPONSE_HANG_TICKS 1200 + static int wait_for_response(struct hv_device *hdev, - struct completion *comp) + struct completion *comp, + const char *msg_type) { + u64 counter = 0; + while (true) { if (hdev->channel->rescind) { dev_warn_once(&hdev->device, "The device is gone.\n"); return -ENODEV; } - if (wait_for_completion_timeout(comp, HZ / 10)) + counter++; + + if (wait_for_completion_timeout(comp, HZ / 10)) { + if (counter > PCI_RESPONSE_HANG_TICKS) + dev_warn(&hdev->device, + "Late %s completion arrived.\n", msg_type); break; + } + + if (counter == PCI_RESPONSE_HANG_TICKS) { + dev_err(&hdev->device, + "%s stuck waiting for response, relid = %u\n", + msg_type, hdev->channel->offermsg.child_relid); + } } return 0; @@ -1518,7 +1537,8 @@ static int hv_read_config_block(struct pci_dev *pdev, void *buf, if (ret) return ret; - ret = wait_for_response(hbus->hdev, &comp_pkt.comp_pkt.host_event); + ret = wait_for_response(hbus->hdev, &comp_pkt.comp_pkt.host_event, + "PCI_READ_BLOCK"); if (ret) return ret; @@ -1607,7 +1627,8 @@ static int hv_write_config_block(struct pci_dev *pdev, void *buf, if (ret) return ret; - ret = wait_for_response(hbus->hdev, &comp_pkt.host_event); + ret = wait_for_response(hbus->hdev, &comp_pkt.host_event, + "PCI_WRITE_BLOCK"); if (ret) return ret; @@ -2624,7 +2645,8 @@ static struct hv_pci_dev *new_pcichild_device(struct hv_pcibus_device *hbus, if (ret) goto error; - if (wait_for_response(hbus->hdev, &comp_pkt.host_event)) + if (wait_for_response(hbus->hdev, &comp_pkt.host_event, + "PCI_QUERY_RESOURCE_REQUIREMENTS")) goto error; hpdev->desc = *desc; @@ -3256,7 +3278,8 @@ static int hv_pci_protocol_negotiation(struct hv_device *hdev, (unsigned long)pkt, VM_PKT_DATA_INBAND, VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED); if (!ret) - ret = wait_for_response(hdev, &comp_pkt.host_event); + ret = wait_for_response(hdev, &comp_pkt.host_event, + "PCI_QUERY_PROTOCOL_VERSION"); if (ret) { dev_err(&hdev->device, @@ -3476,7 +3499,8 @@ static int hv_pci_enter_d0(struct hv_device *hdev) (unsigned long)pkt, VM_PKT_DATA_INBAND, VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED); if (!ret) - ret = wait_for_response(hdev, &comp_pkt.host_event); + ret = wait_for_response(hdev, &comp_pkt.host_event, + "PCI_BUS_D0ENTRY"); if (ret) goto exit; @@ -3553,7 +3577,8 @@ static int hv_pci_query_relations(struct hv_device *hdev) ret = vmbus_sendpacket(hdev->channel, &message, sizeof(message), 0, VM_PKT_DATA_INBAND, 0); if (!ret) - ret = wait_for_response(hdev, &comp); + ret = wait_for_response(hdev, &comp, + "PCI_QUERY_BUS_RELATIONS"); /* * In the case of fast device addition/removal, it's possible that @@ -3644,7 +3669,8 @@ static int hv_send_resources_allocated(struct hv_device *hdev) VM_PKT_DATA_INBAND, VMBUS_DATA_PACKET_FLAG_COMPLETION_REQUESTED); if (!ret) - ret = wait_for_response(hdev, &comp_pkt.host_event); + ret = wait_for_response(hdev, &comp_pkt.host_event, + "PCI_RESOURCE_ASSIGNED"); if (ret) break; -- 2.53.0