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Message-ID: <1514324496.2714.69.camel@decadent.org.uk>
Subject: Re: [PATCH 4.14 015/159] bitops: Add clear/set_bit32() to
 linux/bitops.h
From: Ben Hutchings <ben@decadent.org.uk>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Andi Kleen <ak@linux.intel.com>
Cc: inux-kernel@vger.kernel.org, stable@vger.kernel.org,
        Thomas Gleixner <tglx@linutronix.de>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>
Date: Tue, 26 Dec 2017 21:41:36 +0000
In-Reply-To: <20171222084624.604335610@linuxfoundation.org>
References: <20171222084623.668990192@linuxfoundation.org>
         <20171222084624.604335610@linuxfoundation.org>
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On Fri, 2017-12-22 at 09:45 +0100, Greg Kroah-Hartman wrote:
> 4.14-stable review patch.  If anyone has any objections, please let me kn=
ow.
>=20
> ------------------
>=20
> From: Andi Kleen <ak@linux.intel.com>
>=20
> commit cbe96375025e14fc76f9ed42ee5225120d7210f8 upstream.
>=20
> Add two simple wrappers around set_bit/clear_bit() that accept
> the common case of an u32 array. This avoids writing
> casts in all callers.

These won't work correctly on big-endian 64-bit systems.  They are also
unsafe to use on u32 arrays with an odd length, on 64-bit systems.
This is why lib/bitmap.c has conversion functions for u32 arrays.

Ben.

> Signed-off-by: Andi Kleen <ak@linux.intel.com>
> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Link: http://lkml.kernel.org/r/20171013215645.23166-2-andi@firstfloor.org
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>=20
> ---
>  include/linux/bitops.h |   26 ++++++++++++++++++++++++++
>  1 file changed, 26 insertions(+)
>=20
> --- a/include/linux/bitops.h
> +++ b/include/linux/bitops.h
> @@ -228,6 +228,32 @@ static inline unsigned long __ffs64(u64
>  	return __ffs((unsigned long)word);
>  }
> =20
> +/*
> + * clear_bit32 - Clear a bit in memory for u32 array
> + * @nr: Bit to clear
> + * @addr: u32 * address of bitmap
> + *
> + * Same as clear_bit, but avoids needing casts for u32 arrays.
> + */
> +
> +static __always_inline void clear_bit32(long nr, volatile u32 *addr)
> +{
> +	clear_bit(nr, (volatile unsigned long *)addr);
> +}
> +
> +/*
> + * set_bit32 - Set a bit in memory for u32 array
> + * @nr: Bit to clear
> + * @addr: u32 * address of bitmap
> + *
> + * Same as set_bit, but avoids needing casts for u32 arrays.
> + */
> +
> +static __always_inline void set_bit32(long nr, volatile u32 *addr)
> +{
> +	set_bit(nr, (volatile unsigned long *)addr);
> +}
> +
>  #ifdef __KERNEL__
> =20
>  #ifndef set_mask_bits
>=20
>=20
--=20
Ben Hutchings
The world is coming to an end.	Please log off.


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