FAILED: patch "[PATCH] x86/Hyper-V: Free hv_panic_page when fail to register kmsg" failed to apply to 4.19-stable tree

[<gregkh@linuxfoundation.org>]

The patch below does not apply to the 4.19-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@vger.kernel.org>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 7f11a2cc10a4ae3a70e2c73361f4a9a33503539b Mon Sep 17 00:00:00 2001
From: Tianyu Lan <Tianyu.Lan@microsoft.com>
Date: Mon, 6 Apr 2020 08:53:27 -0700
Subject: [PATCH] x86/Hyper-V: Free hv_panic_page when fail to register kmsg
 dump

If kmsg_dump_register() fails, hv_panic_page will not be used
anywhere.  So free and reset it.

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/20200406155331.2105-3-Tianyu.Lan@microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 6478240d11ab..00a511f15926 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1385,9 +1385,13 @@ static int vmbus_bus_init(void)
 			hv_panic_page = (void *)hv_alloc_hyperv_zeroed_page();
 			if (hv_panic_page) {
 				ret = kmsg_dump_register(&hv_kmsg_dumper);
-				if (ret)
+				if (ret) {
 					pr_err("Hyper-V: kmsg dump register "
 						"error 0x%x\n", ret);
+					hv_free_hyperv_page(
+					    (unsigned long)hv_panic_page);
+					hv_panic_page = NULL;
+				}
 			} else
 				pr_err("Hyper-V: panic message page memory "
 					"allocation failed");
@@ -1416,7 +1420,6 @@ static int vmbus_bus_init(void)
 	hv_remove_vmbus_irq();
 
 	bus_unregister(&hv_bus);
-	hv_free_hyperv_page((unsigned long)hv_panic_page);
 	unregister_sysctl_table(hv_ctl_table_hdr);
 	hv_ctl_table_hdr = NULL;
 	return ret;