linux-kernel - [PATCH 1/1] Drivers: hv: vmbus: Add timeout to vmbus_wait_for

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Message-Id: <1600026449-23651-1-git-send-email-mikelley@microsoft.com>
Date:   Sun, 13 Sep 2020 12:47:29 -0700
From:   Michael Kelley <mikelley@...rosoft.com>
To:     linux-kernel@...r.kernel.org, vkuznets@...hat.com,
        kys@...rosoft.com, sthemmin@...rosoft.com, wei.liu@...nel.org,
        linux-hyperv@...r.kernel.org
Cc:     mikelley@...rosoft.com
Subject: [PATCH 1/1] Drivers: hv: vmbus: Add timeout to vmbus_wait_for_unload

vmbus_wait_for_unload() looks for a CHANNELMSG_UNLOAD_RESPONSE message
coming from Hyper-V.  But if the message isn't found for some reason,
the panic path gets hung forever.  Add a timeout of 10 seconds to prevent
this.

Fixes: 415719160de3 ("Drivers: hv: vmbus: avoid scheduling in interrupt context in vmbus_initiate_unload()")
Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
---
 drivers/hv/channel_mgmt.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 591106c..1d44bb6 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -731,7 +731,7 @@ static void vmbus_wait_for_unload(void)
 	void *page_addr;
 	struct hv_message *msg;
 	struct vmbus_channel_message_header *hdr;
-	u32 message_type;
+	u32 message_type, i;
 
 	/*
 	 * CHANNELMSG_UNLOAD_RESPONSE is always delivered to the CPU which was
@@ -741,8 +741,11 @@ static void vmbus_wait_for_unload(void)
 	 * functional and vmbus_unload_response() will complete
 	 * vmbus_connection.unload_event. If not, the last thing we can do is
 	 * read message pages for all CPUs directly.
+	 *
+	 * Wait no more than 10 seconds so that the panic path can't get
+	 * hung forever in case the response message isn't seen.
 	 */
-	while (1) {
+	for (i = 0; i < 1000; i++) {
 		if (completion_done(&vmbus_connection.unload_event))
 			break;
 
-- 
1.8.3.1