linux-kernel - Re: [PATCH] mips: irq: Use DECLARE

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Date:	Thu, 21 May 2015 09:10:31 -0700
From:	Joe Perches <joe@...ches.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	linux-mips <linux-mips@...ux-mips.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Gabor Juhos <juhosg@...nwrt.org>,
	Manuel Lauss <manuel.lauss@...glemail.com>,
	John Crispin <blogic@...nwrt.org>
Subject: Re: [PATCH] mips: irq: Use DECLARE_BITMAP

On Thu, 2015-05-21 at 15:14 +0200, Ralf Baechle wrote:
> On Wed, May 20, 2015 at 05:44:54AM -0700, Joe Perches wrote:
> 
> > Use the generic mechanism to declare a bitmap instead of unsigned long.
> > 
> > This could fix an overwrite defect of whatever follows irq_map.
> > 
> > Not all "#define NR_IRQS <value>" are a multiple of BITS_PER_LONG so
> > using DECLARE_BITMAP allocates the proper number of longs required
> > for the possible bits.
> > 
> > For instance:
> > 
> > arch/mips/include/asm/mach-ath79/irq.h:#define NR_IRQS                  51
> > arch/mips/include/asm/mach-db1x00/irq.h:#define NR_IRQS 152
> > arch/mips/include/asm/mach-lantiq/falcon/irq.h:#define NR_IRQS 328
> 
> This only matters to user of the allocate_irqno() API and there is only
> on such platform, the IP27 which fortunately uses a NR_IRQS value that
> is a multiple of 64, so no impact.
> 
> Thanks anyway!

I think you should apply it anyway as it's an
error-prone style.

There are 3 mechanisms used today in the kernel
to declare bitmap arrays.

	DECLARE_BITMAP(array, size)
	unsigned long array[BITS_TO_LONGS(size)]
	unsigned long array[size/BITS_PER_LONG]

The first 2 are fine, the last has this defect
possible whenever size % BITS_PER_LONG != 0.

The series I sent converts all the uses of the
the possibly defective style.

cheers, Joe

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