[PATCH 4.4 10/30] Drivers: hv: avoid vfree() on crash

[Greg Kroah-Hartman]

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>

commit a9f61ca793becabdefab03b77568d6c6f8c1bc79 upstream.

When we crash from NMI context (e.g. after NMI injection from host when
'sysctl -w kernel.unknown_nmi_panic=1' is set) we hit

    kernel BUG at mm/vmalloc.c:1530!

as vfree() is denied. While the issue could be solved with in_nmi() check
instead I opted for skipping vfree on all sorts of crashes to reduce the
amount of work which can cause consequent crashes. We don't really need to
free anything on crash.

Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Signed-off-by: K. Y. Srinivasan <kys@xxxxxxxxxxxxx>
Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/hv/hv.c           |    8 +++++---
 drivers/hv/hyperv_vmbus.h |    2 +-
 drivers/hv/vmbus_drv.c    |    8 ++++----
 3 files changed, 10 insertions(+), 8 deletions(-)

--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -274,7 +274,7 @@ cleanup:
  *
  * This routine is called normally during driver unloading or exiting.
  */
-void hv_cleanup(void)
+void hv_cleanup(bool crash)
 {
 	union hv_x64_msr_hypercall_contents hypercall_msr;
 
@@ -284,7 +284,8 @@ void hv_cleanup(void)
 	if (hv_context.hypercall_page) {
 		hypercall_msr.as_uint64 = 0;
 		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
-		vfree(hv_context.hypercall_page);
+		if (!crash)
+			vfree(hv_context.hypercall_page);
 		hv_context.hypercall_page = NULL;
 	}
 
@@ -304,7 +305,8 @@ void hv_cleanup(void)
 
 		hypercall_msr.as_uint64 = 0;
 		wrmsrl(HV_X64_MSR_REFERENCE_TSC, hypercall_msr.as_uint64);
-		vfree(hv_context.tsc_page);
+		if (!crash)
+			vfree(hv_context.tsc_page);
 		hv_context.tsc_page = NULL;
 	}
 #endif
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -581,7 +581,7 @@ struct hv_ring_buffer_debug_info {
 
 extern int hv_init(void);
 
-extern void hv_cleanup(void);
+extern void hv_cleanup(bool crash);
 
 extern int hv_post_message(union hv_connection_id connection_id,
 			 enum hv_message_type message_type,
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -889,7 +889,7 @@ err_alloc:
 	bus_unregister(&hv_bus);
 
 err_cleanup:
-	hv_cleanup();
+	hv_cleanup(false);
 
 	return ret;
 }
@@ -1254,7 +1254,7 @@ static void hv_kexec_handler(void)
 	vmbus_initiate_unload();
 	for_each_online_cpu(cpu)
 		smp_call_function_single(cpu, hv_synic_cleanup, NULL, 1);
-	hv_cleanup();
+	hv_cleanup(false);
 };
 
 static void hv_crash_handler(struct pt_regs *regs)
@@ -1266,7 +1266,7 @@ static void hv_crash_handler(struct pt_r
 	 * for kdump.
 	 */
 	hv_synic_cleanup(NULL);
-	hv_cleanup();
+	hv_cleanup(true);
 };
 
 static int __init hv_acpi_init(void)
@@ -1330,7 +1330,7 @@ static void __exit vmbus_exit(void)
 						 &hyperv_panic_block);
 	}
 	bus_unregister(&hv_bus);
-	hv_cleanup();
+	hv_cleanup(false);
 	for_each_online_cpu(cpu) {
 		tasklet_kill(hv_context.event_dpc[cpu]);
 		smp_call_function_single(cpu, hv_synic_cleanup, NULL, 1);