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Date:   Mon, 31 Oct 2016 21:46:09 -0700 (PDT)
From:   Dongli Zhang <>
To:     <>, JBeulich <>
Cc:     <>, <>,
        <>, <>,
        <>, <>
Subject: Re: [PATCH 1/1] xen-netfront: do not cast grant table reference to
 signed short

Hi David and Jan,

I did more testing on the code. Casting to either (long) or (unsigned long)
would be fine.

However, there is still an issue that ref is of type uint32_t and
IS_ERR_VALUE((unsigned long)ref) would not return true when ref=-ENOSPC (or
other error code).

IS_ERR_VALUE((long)ref) would return false as well.

The solution is to cast ref to (int) first as follows:

-   BUG_ON((signed short)ref < 0);
+   WARN_ON_ONCE(IS_ERR_VALUE((unsigned long)(int)ref));

David, I am very sorry for this error and I will be careful the next time.
Would you please let me know if I should resend a new patch or an incremental
based on previous one at

Thank you very much!

Dongli Zhang

----- Original Message -----
Sent: Tuesday, November 1, 2016 4:06:27 AM GMT +08:00 Beijing / Chongqing / Hong Kong / Urumqi
Subject: Re: [PATCH 1/1] xen-netfront: do not cast grant table reference to signed short

From: Dongli Zhang <>
Date: Mon, 31 Oct 2016 13:38:29 +0800

> While grant reference is of type uint32_t, xen-netfront erroneously casts
> it to signed short in BUG_ON().
> This would lead to the xen domU panic during boot-up or migration when it
> is attached with lots of paravirtual devices.
> Signed-off-by: Dongli Zhang <>

Since this is consistent with how the macros in linux/err.h handle "is
this an error" checks, this change looks good to me.

Applied, thanks.

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