linux-kernel - Re: [PATCH] net: sxgbe: fix error paths in sxgbe_platform

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Message-ID: <87r3ev8urb.fsf@rasmusvillemoes.dk>
Date:	Sun, 27 Mar 2016 23:40:24 +0200
From:	Rasmus Villemoes <linux@...musvillemoes.dk>
To:	Francois Romieu <romieu@...zoreil.com>
Cc:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: sxgbe: fix error paths in sxgbe_platform_probe()

On Sun, Mar 27 2016, Francois Romieu <romieu@...zoreil.com> wrote:

> Rasmus Villemoes <linux@...musvillemoes.dk> :
>> We need to use post-decrement to ensure that irq_dispose_mapping is
>> also called on priv->rxq[0]->irq_no; moreover, if one of the above for
>> loops failed already at i==0 (so we reach one of these labels with
>> that value of i), we'll enter an essentially infinite loop of
>> out-of-bounds accesses.
>> 
>> Signed-off-by: Rasmus Villemoes <linux@...musvillemoes.dk>
>
> (ok, i is signed)
>
> Reviewed-by: Francois Romieu <romieu@...zoreil.com>
>

Thanks for reviewing, but just FTR I want to point out that it doesn't
matter whether i is signed or not in

  while (i--)

However, when i is signed, there's another slightly less popular variant
which is equivalent:

  while (--i >= 0)

(a precondition for their equivalence is that i has a non-negative value
before reaching the while statement).

Neither are equivalent to the almost-always broken

  while (--i)

Rasmus