linux-kernel - Re: [PATCH V2 2/3] scsi: fix compiler warning for sg

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Date:	Mon, 9 Nov 2015 16:14:50 +0200
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	Sinan Kaya <okaya@...eaurora.org>
Cc:	linux-scsi <linux-scsi@...r.kernel.org>, timur@...eaurora.org,
	cov@...eaurora.org, jcm@...hat.com,
	Andy Gross <agross@...eaurora.org>,
	linux-arm-msm@...r.kernel.org,
	linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
	Doug Gilbert <dgilbert@...erlog.com>,
	"James E.J. Bottomley" <JBottomley@...n.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 2/3] scsi: fix compiler warning for sg

On Mon, Nov 9, 2015 at 3:57 AM, Sinan Kaya <okaya@...eaurora.org> wrote:
> The MULDIV macro has been designed for small numbers.
> Compiler emits an overflow warning on 64 bit systems.
> This patch uses 64 bit numbers in order to suppress
> warning.
>
> Signed-off-by: Sinan Kaya <okaya@...eaurora.org>


> ---
>  drivers/scsi/sg.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/scsi/sg.c b/drivers/scsi/sg.c
> index 9d7b7db..112d8974 100644
> --- a/drivers/scsi/sg.c
> +++ b/drivers/scsi/sg.c
> @@ -51,6 +51,7 @@ static int sg_version_num = 30536;    /* 2 digits for each component */
>  #include <linux/atomic.h>
>  #include <linux/ratelimit.h>
>  #include <linux/uio.h>
> +#include <asm/div64.h>
>
>  #include "scsi.h"
>  #include <scsi/scsi_dbg.h>
> @@ -85,12 +86,17 @@ static void sg_proc_cleanup(void);
>   * Replacing muldiv(x) by muldiv(x)=((x % d) * m) / d + int(x / d) * m
>   * calculates the same, but prevents the overflow when both m and d
>   * are "small" numbers (like HZ and USER_HZ).
> - * Of course an overflow is inavoidable if the result of muldiv doesn't fit
> - * in 32 bits.
>   */
> -#define MULDIV(X,MUL,DIV) ((((X % DIV) * MUL) / DIV) + ((X / DIV) * MUL))
> +static inline u64 mult_frac64(u64 x, u32 numer, u32 denom)
> +{
> +       u64 r1 = do_div(x, denom);
> +       u64 r2 = r1 * numer;
> +
> +       do_div(r2, denom);

> +       return (x * numer) + r2;

Parens are useless, noticed later, sorry.

Isn't mult_frac() enough here?

Btw, can you mention explicitly what is the warning you get
(copy'n'paste of the line would be okay)?

> +}
>
> -#define SG_DEFAULT_TIMEOUT MULDIV(SG_DEFAULT_TIMEOUT_USER, HZ, USER_HZ)
> +#define SG_DEFAULT_TIMEOUT mult_frac64(SG_DEFAULT_TIMEOUT_USER, HZ, USER_HZ)
>
>  int sg_big_buff = SG_DEF_RESERVED_SIZE;
>  /* N.B. This variable is readable and writeable via
> @@ -877,10 +883,10 @@ sg_ioctl(struct file *filp, unsigned int cmd_in, unsigned long arg)
>                         return result;
>                 if (val < 0)
>                         return -EIO;
> -               if (val >= MULDIV (INT_MAX, USER_HZ, HZ))
> -                   val = MULDIV (INT_MAX, USER_HZ, HZ);
> +               if (val >= mult_frac64(INT_MAX, USER_HZ, HZ))
> +                       val = mult_frac64(INT_MAX, USER_HZ, HZ);


>                 sfp->timeout_user = val;
> -               sfp->timeout = MULDIV (val, HZ, USER_HZ);
> +               sfp->timeout = mult_frac64(val, HZ, USER_HZ);
>
>                 return 0;
>         case SG_GET_TIMEOUT:    /* N.B. User receives timeout as return value */
> --
> Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
> Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a Linux Foundation Collaborative Project
>
> --
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-- 
With Best Regards,
Andy Shevchenko
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