From: Chris Co <chrco@xxxxxxxxxxxxx>
When invoking kexec() on a Linux guest running on a Hyper-V host, the
kernel panics.
RIP: 0010:cpuhp_issue_call+0x137/0x140
Call Trace:
__cpuhp_remove_state_cpuslocked+0x99/0x100
__cpuhp_remove_state+0x1c/0x30
hv_kexec_handler+0x23/0x30 [hv_vmbus]
hv_machine_shutdown+0x1e/0x30
machine_shutdown+0x10/0x20
kernel_kexec+0x6d/0x96
__do_sys_reboot+0x1ef/0x230
__x64_sys_reboot+0x1d/0x20
do_syscall_64+0x6b/0x3d8
entry_SYSCALL_64_after_hwframe+0x44/0xa9
This was due to hv_synic_cleanup() callback returning -EBUSY to
cpuhp_issue_call() when tearing down the VMBUS_CONNECT_CPU, even
if the vmbus_connection.conn_state = DISCONNECTED. hv_synic_cleanup()
should succeed in the case where vmbus_connection.conn_state
is DISCONNECTED.
Fix is to add an extra condition to test for
vmbus_connection.conn_state == CONNECTED on the VMBUS_CONNECT_CPU and
only return early if true. This way the kexec() path can still shut
everything down while preserving the initial behavior of preventing
CPU offlining on the VMBUS_CONNECT_CPU while the VM is running.
Fixes: 8a857c55420f29 ("Drivers: hv: vmbus: Always handle the VMBus messages on CPU0")
Signed-off-by: Chris Co <chrco@xxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
drivers/hv/hv.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/hv/hv.c b/drivers/hv/hv.c
index 0cde10fe0e71..f202ac7f4b3d 100644
--- a/drivers/hv/hv.c
+++ b/drivers/hv/hv.c
@@ -244,9 +244,13 @@ int hv_synic_cleanup(unsigned int cpu)
/*
* Hyper-V does not provide a way to change the connect CPU once
- * it is set; we must prevent the connect CPU from going offline.
+ * it is set; we must prevent the connect CPU from going offline
+ * while the VM is running normally. But in the panic or kexec()
+ * path where the vmbus is already disconnected, the CPU must be
+ * allowed to shut down.
*/
- if (cpu == VMBUS_CONNECT_CPU)
+ if (cpu == VMBUS_CONNECT_CPU &&
+ vmbus_connection.conn_state == CONNECTED)
return -EBUSY;
/*
--
2.17.1
