linux-kernel - Re: [PATCH] Drivers: hv: vmbus: Allow cleanup of VMBUS_CONNECT

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Date:   Wed, 11 Nov 2020 10:59:18 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Andrea Parri <parri.andrea@...il.com>
Cc:     Chris Co <chrco@...ux.microsoft.com>, linux-hyperv@...r.kernel.org,
        kys@...rosoft.com, haiyangz@...rosoft.com, sthemmin@...rosoft.com,
        wei.liu@...nel.org, chrco@...rosoft.com, mikelley@...rosoft.com,
        andrea.parri@...rosoft.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Drivers: hv: vmbus: Allow cleanup of VMBUS_CONNECT_CPU
 if disconnected

On Tue, Nov 10, 2020 at 09:18:33PM +0100, Andrea Parri wrote:
> On Tue, Nov 10, 2020 at 07:01:18PM +0000, Chris Co wrote:
> > From: Chris Co <chrco@...rosoft.com>
> > 
> > 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@...rosoft.com>
> > Cc: stable@...r.kernel.org
> 
> Reviewed-by: Andrea Parri (Microsoft) <parri.andrea@...il.com>

Applied to hyperv-fixes. Thanks Chris and Andrea.

Wei.