This is a note to let you know that I've just added the patch titled Drivers: hv: vmbus: Allow cleanup of VMBUS_CONNECT_CPU if disconnected to the 5.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drivers-hv-vmbus-allow-cleanup-of-vmbus_connect_cpu-if-disconnected.patch and it can be found in the queue-5.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 92e4dc8b05663d6539b1b8375f3b1cf7b204cfe9 Mon Sep 17 00:00:00 2001 From: Chris Co <chrco@xxxxxxxxxxxxx> Date: Tue, 10 Nov 2020 19:01:18 +0000 Subject: Drivers: hv: vmbus: Allow cleanup of VMBUS_CONNECT_CPU if disconnected From: Chris Co <chrco@xxxxxxxxxxxxx> commit 92e4dc8b05663d6539b1b8375f3b1cf7b204cfe9 upstream. 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> Reviewed-by: Andrea Parri (Microsoft) <parri.andrea@xxxxxxxxx> Cc: stable@xxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/20201110190118.15596-1-chrco@xxxxxxxxxxxxxxxxxxx Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/hv/hv.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/drivers/hv/hv.c +++ b/drivers/hv/hv.c @@ -251,9 +251,13 @@ 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; /* Patches currently in stable-queue which might be from chrco@xxxxxxxxxxxxx are queue-5.4/drivers-hv-vmbus-allow-cleanup-of-vmbus_connect_cpu-if-disconnected.patch