linux-kernel - Re: [PATCH v2] serial: vt8500_serial: Fix a parameter of find_first_zero

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Date:   Wed, 24 Aug 2016 09:21:26 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        linux@...sktech.co.nz, gregkh@...uxfoundation.org, jslaby@...e.com,
        kernel-janitors@...r.kernel.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] serial: vt8500_serial: Fix a parameter of find_first_zero_bit.

On Wednesday, August 24, 2016 7:06:58 AM CEST Christophe JAILLET wrote:
> The 2nd parameter of 'find_first_zero_bit' is the number of bits to search.
> In this case, we are passing 'sizeof(vt8500_ports_in_use)'.
> 'vt8500_ports_in_use' is an 'unsigned long'. So the sizeof is likely to
> return 4 on a 32 bits kernel.
> 
> A few lines below, we check if it is below VT8500_MAX_PORTS, which is 6.
> 
> It is likely that the number of bits in a long was expected here.
> 
> In order to fix it:
>    - use DECLARE_BITMAP when declaring the vt8500_ports_in_use
>    - use VT8500_MAX_PORTS as a maximum value when checking/setting bits in
>      this bitmap
>    - modify code now that 'vt8500_ports_in_use' has become a pointer
>      because of the use of DECLARE_BITMAP
> 
> 
> It has been spotted by the following coccinelle script:
> @@
> expression ret, x;
> 
> @@
> *  ret = \(find_first_bit \| find_first_zero_bit\) (x, sizeof(...));
> 
> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
> ---
> v2: - use of VT8500_MAX_PORTS instead of BITS_PER_LONG to better self
>       document the code
>     - declare vt8500_ports_in_use with DECLARE_BITMAP in order to self
>       document even better and to be foolproof should VT8500_MAX_PORTS
>       be changed one day

Reviewed-by: Arnd Bergmann <arnd@...db.de>