linux-kernel - Re: [PATCH v4] bitops: Fix shift overflow in GENMASK macros

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Date:	Thu, 13 Nov 2014 14:09:36 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Maxime COQUELIN <maxime.coquelin@...com>
Cc:	linux@...musvillemoes.dk, gong.chen@...ux.intel.com,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	" Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, tytso@....edu,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel@...inux.com, eric.paire@...com
Subject: Re: [PATCH v4] bitops: Fix shift overflow in GENMASK macros

On Thu,  6 Nov 2014 10:54:19 +0100 Maxime COQUELIN <maxime.coquelin@...com> wrote:

> On some 32 bits architectures, including x86, GENMASK(31, 0) returns 0
> instead of the expected ~0UL.
> 
> This is the same on some 64 bits architectures with GENMASK_ULL(63, 0).
> 
> This is due to an overflow in the shift operand, 1 << 32 for GENMASK,
> 1 << 64 for GENMASK_ULL.
> 
> Fixes: 10ef6b0dffe404bcc54e94cb2ca1a5b18445a66b
> Cc: <stable@...r.kernel.org> #v3.13+
> Reported-by: Eric Paire <eric.paire@...com>
> Suggested-by: Rasmus Villemoes <linux@...musvillemoes.dk>
> Signed-off-by: Maxime Coquelin <maxime.coquelin@...com>

Why cc:stable?  Does this bug cause some observed kernel misbehaviour? 
If so, please fully describe that in the changelog.  This will help
people to determine whether this patch might fix a bug they're
observing, and will help them to decide whether they should backport
this patch into their kernels.

I'm assuming that Peter will be merging this patch.

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