ACK: [bionic:linux-azure-4.15, focal:linux-azure][PATCH 1/1] UBUNTU: SAUCE: Drivers: hv: vmbus: Add timeout to vmbus_wait_for_unload

[Ian May]

LGTM

Acked-by: Ian May <ian.may at canonical.com>

On 2020-09-17 14:19:01 , Marcelo Henrique Cerri wrote:
> From: Michael Kelley <mikelley at microsoft.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/1895527
> 
> vmbus_wait_for_unload() looks for a CHANNELMSG_UNLOAD_RESPONSE message
> coming from Hyper-V.  But if the message isn't found for some reason,
> the panic path gets hung forever.  Add a timeout of 10 seconds to prevent
> this.
> 
> Fixes: 415719160de3 ("Drivers: hv: vmbus: avoid scheduling in interrupt context in vmbus_initiate_unload()")
> Signed-off-by: Michael Kelley <mikelley at microsoft.com>
> Reviewed-by: Dexuan Cui <decui at microsoft.com>
> Reviewed-by: Vitaly Kuznetsov <vkuznets at redhat.com>
> 
> Link: https://lore.kernel.org/linux-hyperv/1600026449-23651-1-git-send-email-mikelley@microsoft.com/
> Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri at canonical.com>
> ---
>  drivers/hv/channel_mgmt.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
> index 501c43c5851d..452307c79e4b 100644
> --- a/drivers/hv/channel_mgmt.c
> +++ b/drivers/hv/channel_mgmt.c
> @@ -769,7 +769,7 @@ static void vmbus_wait_for_unload(void)
>  	void *page_addr;
>  	struct hv_message *msg;
>  	struct vmbus_channel_message_header *hdr;
> -	u32 message_type;
> +	u32 message_type, i;
>  
>  	/*
>  	 * CHANNELMSG_UNLOAD_RESPONSE is always delivered to the CPU which was
> @@ -779,8 +779,11 @@ static void vmbus_wait_for_unload(void)
>  	 * functional and vmbus_unload_response() will complete
>  	 * vmbus_connection.unload_event. If not, the last thing we can do is
>  	 * read message pages for all CPUs directly.
> +	 *
> +	 * Wait no more than 10 seconds so that the panic path can't get
> +	 * hung forever in case the response message isn't seen.
>  	 */
> -	while (1) {
> +	for (i = 0; i < 1000; i++) {
>  		if (completion_done(&vmbus_connection.unload_event))
>  			break;
>  
> -- 
> 2.25.1
> 
> 
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