Drivers: hv: vmbus: Fix potential crash on module unload

[ Upstream commit 792f232d57ff28bbd5f9c4abe0466b23d5879dc8 ]

The vmbus driver relies on the panic notifier infrastructure to perform
some operations when a panic event is detected. Since vmbus can be built
as module, it is required that the driver handles both registering and
unregistering such panic notifier callback.

After commit 74347a99e73a ("x86/Hyper-V: Unload vmbus channel in hv panic callback")
though, the panic notifier registration is done unconditionally in the module
initialization routine whereas the unregistering procedure is conditionally
guarded and executes only if HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE capability
is set.

This patch fixes that by unconditionally unregistering the panic notifier
in the module's exit routine as well.

Fixes: 74347a99e73a ("x86/Hyper-V: Unload vmbus channel in hv panic callback")
Signed-off-by: Guilherme G. Piccoli <gpiccoli@igalia.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20220315203535.682306-1-gpiccoli@igalia.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 6b7ab8f234e8707b4f9c1e9850b1287297d1b84a..943654ded73d0b00cf45ee19dd9f19659884d2cf 100644 (file)
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -2493,10 +2493,15 @@ static void __exit vmbus_exit(void)
        if (ms_hyperv.misc_features & HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE) {
                kmsg_dump_unregister(&hv_kmsg_dumper);
                unregister_die_notifier(&hyperv_die_block);
-               atomic_notifier_chain_unregister(&panic_notifier_list,
-                                                &hyperv_panic_block);
        }
 
+       /*
+        * The panic notifier is always registered, hence we should
+        * also unconditionally unregister it here as well.
+        */
+       atomic_notifier_chain_unregister(&panic_notifier_list,
+                                        &hyperv_panic_block);
+
        free_page((unsigned long)hv_panic_page);
        unregister_sysctl_table(hv_ctl_table_hdr);
        hv_ctl_table_hdr = NULL;