[bionic:linux-azure-4.15][PATCH 5/9] x86/Hyper-V: Free hv_panic_page when fail to register kmsg dump

[Marcelo Henrique Cerri]

From: Tianyu Lan <Tianyu.Lan at microsoft.com>

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

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 at microsoft.com>
Signed-off-by: Tianyu Lan <Tianyu.Lan at microsoft.com>
Link: https://lore.kernel.org/r/20200406155331.2105-3-Tianyu.Lan@microsoft.com
Signed-off-by: Wei Liu <wei.liu at kernel.org>
(backported from commit 7f11a2cc10a4ae3a70e2c73361f4a9a33503539b)
[mc: fixed context]
Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
---
 drivers/hv/vmbus_drv.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 15a6d43234c5..9b156b476669 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -1204,9 +1204,13 @@ static int vmbus_bus_init(void)
 			hv_panic_page = (void *)get_zeroed_page(GFP_KERNEL);
 			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);
+					free_page(
+					    (unsigned long)hv_panic_page);
+					hv_panic_page = NULL;
+				}
 			} else
 				pr_err("Hyper-V: panic message page memory "
 					"allocation failed");
@@ -1234,7 +1238,6 @@ static int vmbus_bus_init(void)
 	hv_remove_vmbus_irq();
 
 	bus_unregister(&hv_bus);
-	free_page((unsigned long)hv_panic_page);
 	unregister_sysctl_table(hv_ctl_table_hdr);
 	hv_ctl_table_hdr = NULL;
 	return ret;
-- 
2.25.1