[PATCH 1/1] Drivers: hv: vmbus: Fix crash handler reset of Hyper-V synic

[PATCH 1/1] Drivers: hv: vmbus: Fix crash handler reset of Hyper-V synic

[Michael Kelley]

The crash handler calls hv_synic_cleanup() to shutdown the
Hyper-V synthetic interrupt controller.  But if the CPU
that calls hv_synic_cleanup() has a VMbus channel interrupt
assigned to it (which is likely the case in smaller VM sizes),
hv_synic_cleanup() returns an error and the synthetic
interrupt controller isn't shutdown.  While the lack of
being shutdown hasn't caused a known problem, it still
should be fixed for highest reliability.

So directly call hv_synic_disable_regs() instead of
hv_synic_cleanup(), which ensures that the synic is always
shutdown.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
---
 drivers/hv/vmbus_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
index 664a415..665920d 100644
--- a/drivers/hv/vmbus_drv.c
+++ b/drivers/hv/vmbus_drv.c
@@ -2305,7 +2305,7 @@ static void hv_crash_handler(struct pt_regs *regs)
 	vmbus_connection.conn_state = DISCONNECTED;
 	cpu = smp_processor_id();
 	hv_stimer_cleanup(cpu);
-	hv_synic_cleanup(cpu);
+	hv_synic_disable_regs(cpu);
 	hyperv_cleanup();
 };
 
-- 
1.8.3.1

Re: [PATCH 1/1] Drivers: hv: vmbus: Fix crash handler reset of Hyper-V synic

[Vitaly Kuznetsov]

Michael Kelley <mikelley@microsoft.com> writes:

> The crash handler calls hv_synic_cleanup() to shutdown the
> Hyper-V synthetic interrupt controller.  But if the CPU
> that calls hv_synic_cleanup() has a VMbus channel interrupt
> assigned to it (which is likely the case in smaller VM sizes),
> hv_synic_cleanup() returns an error and the synthetic
> interrupt controller isn't shutdown.  While the lack of
> being shutdown hasn't caused a known problem, it still
> should be fixed for highest reliability.
>
> So directly call hv_synic_disable_regs() instead of
> hv_synic_cleanup(), which ensures that the synic is always
> shutdown.

Generally, when performing kdump doing as little work as possible is
always preferred and hv_synic_cleanup() does too much: taking mutex,
walking through channel list,... 

Also, hv_synic_cleanup() was calling hv_stimer_cleanup() and we have a
second redundant invocation in hv_crash_handler().

>
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> ---
>  drivers/hv/vmbus_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 664a415..665920d 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -2305,7 +2305,7 @@ static void hv_crash_handler(struct pt_regs *regs)
>  	vmbus_connection.conn_state = DISCONNECTED;
>  	cpu = smp_processor_id();
>  	hv_stimer_cleanup(cpu);
> -	hv_synic_cleanup(cpu);
> +	hv_synic_disable_regs(cpu);
>  	hyperv_cleanup();
>  };

Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>

-- 
Vitaly

RE: [PATCH 1/1] Drivers: hv: vmbus: Fix crash handler reset of Hyper-V synic

[Dexuan Cui]

> From: Michael Kelley <mikelley@microsoft.com>
> Sent: Wednesday, November 13, 2019 10:32 PM
> To: linux-kernel@vger.kernel.org; vkuznets <vkuznets@redhat.com>; KY
> Srinivasan <kys@microsoft.com>; Stephen Hemminger
> <sthemmin@microsoft.com>; sashal@kernel.org; Dexuan Cui
> <decui@microsoft.com>; linux-hyperv@vger.kernel.org
> Cc: Michael Kelley <mikelley@microsoft.com>
> Subject: [PATCH 1/1] Drivers: hv: vmbus: Fix crash handler reset of Hyper-V
> synic
> 
> The crash handler calls hv_synic_cleanup() to shutdown the
> Hyper-V synthetic interrupt controller.  But if the CPU
> that calls hv_synic_cleanup() has a VMbus channel interrupt
> assigned to it (which is likely the case in smaller VM sizes),
> hv_synic_cleanup() returns an error and the synthetic
> interrupt controller isn't shutdown.  While the lack of
> being shutdown hasn't caused a known problem, it still
> should be fixed for highest reliability.
> 
> So directly call hv_synic_disable_regs() instead of
> hv_synic_cleanup(), which ensures that the synic is always
> shutdown.
> 
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> ---
>  drivers/hv/vmbus_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index 664a415..665920d 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -2305,7 +2305,7 @@ static void hv_crash_handler(struct pt_regs *regs)
>  	vmbus_connection.conn_state = DISCONNECTED;
>  	cpu = smp_processor_id();
>  	hv_stimer_cleanup(cpu);
> -	hv_synic_cleanup(cpu);
> +	hv_synic_disable_regs(cpu);
>  	hyperv_cleanup();
>  };
> 
> --

Reviewed-by: Dexuan Cui <decui@microsoft.com>

Re: [PATCH 1/1] Drivers: hv: vmbus: Fix crash handler reset of Hyper-V synic

[Sasha Levin]

On Thu, Nov 14, 2019 at 06:32:01AM +0000, Michael Kelley wrote:
>The crash handler calls hv_synic_cleanup() to shutdown the
>Hyper-V synthetic interrupt controller.  But if the CPU
>that calls hv_synic_cleanup() has a VMbus channel interrupt
>assigned to it (which is likely the case in smaller VM sizes),
>hv_synic_cleanup() returns an error and the synthetic
>interrupt controller isn't shutdown.  While the lack of
>being shutdown hasn't caused a known problem, it still
>should be fixed for highest reliability.
>
>So directly call hv_synic_disable_regs() instead of
>hv_synic_cleanup(), which ensures that the synic is always
>shutdown.
>
>Signed-off-by: Michael Kelley <mikelley@microsoft.com>

Queued up, thank you.

-- 
Thanks,
Sasha