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

Andy Shevchenko
2015-11-09T14:14:50Z

On Mon, Nov 9, 2015 at 3:57 AM, Sinan Kaya <okaya@codeaurora.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@codeaurora.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