Re: [win-pv-devel] [PATCH] Fix BSOD on RingDestroy

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: win-pv-devel [mailto:win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx] On
> Behalf Of Owen Smith
> Sent: 25 September 2018 16:30
> To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx
> Cc: Owen Smith <owen.smith@xxxxxxxxxx>
> Subject: [win-pv-devel] [PATCH] Fix BSOD on RingDestroy
> 
> Zero Frontend->MaxQueues after calling RingDestroy, as RingDestroy will
> query this value to free each BlkifRing, which will decrement an
> unsigned value below 0.
> Also adds an ASSERT to detect if FrontendGetMaxQueues returns 0.
> 
> Signed-off-by: Owen Smith <owen.smith@xxxxxxxxxx>

Acked-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

> ---
>  src/xenvbd/frontend.c | 4 ++--
>  src/xenvbd/ring.c     | 1 +
>  2 files changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/src/xenvbd/frontend.c b/src/xenvbd/frontend.c
> index 987d237..b12e122 100644
> --- a/src/xenvbd/frontend.c
> +++ b/src/xenvbd/frontend.c
> @@ -1976,8 +1976,6 @@ FrontendDestroy(
>      Frontend->Page83.Data = NULL;
>      Frontend->Page83.Size = 0;
> 
> -    Frontend->MaxQueues = 0;
> -
>      ThreadAlert(Frontend->BackendThread);
>      ThreadJoin(Frontend->BackendThread);
>      Frontend->BackendThread = NULL;
> @@ -1988,6 +1986,8 @@ FrontendDestroy(
>      RingDestroy(Frontend->Ring);
>      Frontend->Ring = NULL;
> 
> +    Frontend->MaxQueues = 0;
> +
>      ASSERT3P(Frontend->BackendPath, ==, NULL);
>      ASSERT3P(Frontend->BackendWatch, ==, NULL);
> 
> diff --git a/src/xenvbd/ring.c b/src/xenvbd/ring.c
> index d595226..d13afcf 100644
> --- a/src/xenvbd/ring.c
> +++ b/src/xenvbd/ring.c
> @@ -2338,6 +2338,7 @@ RingDestroy(
>      ULONG               Index;
> 
>      Index = FrontendGetMaxQueues(Ring->Frontend);
> +     ASSERT3U(Index, >, 0);
> 
>      while (--Index > 0) {
>          PXENVBD_BLKIF_RING  BlkifRing = Ring->Ring[Index];
> --
> 2.16.2.windows.1
> 
> 
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