Re: [PATCH 1/5] Improve transmitter disable.

[Paul Durrant <xadimgnik@xxxxxxxxx>]

On 28/07/2021 15:02, Martin Harvey wrote:
> In some cases, the backend may stop processing Tx ring
> requests in a timely manner. If this happens at the same time as ring
> disable, then the Tx code could spin forever at dispatch IRQL.
>
> This patch introduces a hard limit on how long the code will spin,
> allowing a device disable or power transition to complete, albeit
> at the cost of Tx requests being dropped or the ring being in
> an indeterminate state. This has normally been seen at guest shutdown
> where final ring state is of little consequence.
>
> Signed-off-by: Martin Harvey <martin.harvey@xxxxxxxxxx>
Acked-by: Paul Durrant <paul@xxxxxxx>

> ---
>   src/xenvif/transmitter.c | 14 +++++++++-----
>   1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/src/xenvif/transmitter.c b/src/xenvif/transmitter.c
> index f6935a6..fddeb0c 100644
> --- a/src/xenvif/transmitter.c
> +++ b/src/xenvif/transmitter.c
> @@ -3988,21 +3988,25 @@ __TransmitterRingDisable(
>       ASSERT3U(Ring->RequestsPushed, ==, Ring->RequestsPosted);
>       while (Ring->ResponsesProcessed != Ring->RequestsPushed) {
>           Attempt++;
> -        ASSERT(Attempt < 100);
> +
> +        KeStallExecutionProcessor(1000);    // 1ms
>   
>           // Try to move things along
>           __TransmitterRingSend(Ring);
>           (VOID) TransmitterRingPoll(Ring);
>   
> -        if (State != XenbusStateConnected)
> -            __TransmitterRingFakeResponses(Ring);
> +        if ((Attempt >= 100) || (State != XenbusStateConnected))
> +            break;
>   
>           // We are waiting for a watch event at DISPATCH_LEVEL so
>           // it is our responsibility to poll the store ring.
>           XENBUS_STORE(Poll,
>                        &Transmitter->StoreInterface);
> -
> -        KeStallExecutionProcessor(1000);    // 1ms
> +    }
> +    if (Ring->ResponsesProcessed != Ring->RequestsPushed)
> +    {
> +        __TransmitterRingFakeResponses(Ring);
> +        (VOID) TransmitterRingPoll(Ring);
>       }
>   
>       Ring->Enabled = FALSE;