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[bionic:linux-azure-4.15,4/9] x86/Hyper-V: Unload vmbus channel in hv panic callback

Message ID 20200616025842.102415-5-marcelo.cerri@canonical.com
State New
Headers show
Series LP:#1875456 - Azure diagnostic/serviceability improvement | expand

Commit Message

Marcelo Henrique Cerri June 16, 2020, 2:58 a.m. UTC 
From: Tianyu Lan <Tianyu.Lan@microsoft.com>

BugLink: http://bugs.launchpad.net/bugs/1875456

When kdump is not configured, a Hyper-V VM might still respond to
network traffic after a kernel panic when kernel parameter panic=0.
The panic CPU goes into an infinite loop with interrupts enabled,
and the VMbus driver interrupt handler still works because the
VMbus connection is unloaded only in the kdump path.  The network
responses make the other end of the connection think the VM is
still functional even though it has panic'ed, which could affect any
failover actions that should be taken.

Fix this by unloading the VMbus connection during the panic process.
vmbus_initiate_unload() could then be called twice (e.g., by
hyperv_panic_event() and hv_crash_handler(), so reset the connection
state in vmbus_initiate_unload() to ensure the unload is done only
once.

Fixes: 81b18bce48af ("Drivers: HV: Send one page worth of kmsg dump over Hyper-V during panic")
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Link: https://lore.kernel.org/r/20200406155331.2105-2-Tianyu.Lan@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
(backported from commit 74347a99e73ae00b8385f1209aaea193c670f901)
[mc: fixed context and skipped vmbus_bus_suspend()]
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@canonical.com>
---
 drivers/hv/channel_mgmt.c |  3 +++
 drivers/hv/vmbus_drv.c    | 19 +++++++++++++------
 2 files changed, 16 insertions(+), 6 deletions(-)
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Patch

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 06a6a01c0b31..d7ccd62848c8 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -844,6 +844,9 @@  void vmbus_initiate_unload(bool crash)
 {
 	struct vmbus_channel_message_header hdr;
 
+	if (xchg(&vmbus_connection.conn_state, DISCONNECTED) == DISCONNECTED)
+		return;
+
 	/* Pre-Win2012R2 hosts don't support reconnect */
 	if (vmbus_proto_version < VERSION_WIN8_1)
 		return;
diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 678576db5273..15a6d43234c5 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -63,9 +63,12 @@  static int hyperv_panic_event(struct notifier_block *nb, unsigned long val,
 {
 	struct pt_regs *regs;
 
-	regs = current_pt_regs();
+	vmbus_initiate_unload(true);
 
-	hyperv_report_panic(regs, val);
+	if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
+		regs = current_pt_regs();
+		hyperv_report_panic(regs, val);
+	}
 	return NOTIFY_DONE;
 }
 
@@ -1210,10 +1213,16 @@  static int vmbus_bus_init(void)
 		}
 
 		register_die_notifier(&hyperv_die_block);
-		atomic_notifier_chain_register(&panic_notifier_list,
-					       &hyperv_panic_block);
 	}
 
+	/*
+	 * Always register the panic notifier because we need to unload
+	 * the VMbus channel connection to prevent any VMbus
+	 * activity after the VM panics.
+	 */
+	atomic_notifier_chain_register(&panic_notifier_list,
+			       &hyperv_panic_block);
+
 	vmbus_request_offers();
 
 	return 0;
@@ -1840,7 +1849,6 @@  static void hv_kexec_handler(void)
 {
 	hv_synic_clockevents_cleanup();
 	vmbus_initiate_unload(false);
-	vmbus_connection.conn_state = DISCONNECTED;
 	/* Make sure conn_state is set as hv_synic_cleanup checks for it */
 	mb();
 	cpuhp_remove_state(hyperv_cpuhp_online);
@@ -1855,7 +1863,6 @@  static void hv_crash_handler(struct pt_regs *regs)
 	 * doing the cleanup for current CPU only. This should be sufficient
 	 * for kdump.
 	 */
-	vmbus_connection.conn_state = DISCONNECTED;
 	hv_synic_cleanup(smp_processor_id());
 	hyperv_cleanup();
 };