Re: [PATCH v2 2/4] block: fix ioprio interface

[Hannes Reinecke <hare@suse.de>]

On 8/6/21 7:11 AM, Damien Le Moal wrote:
> An iocb aio_reqprio field is 16-bits (u16) but often handled as an int
> in the block layer. E.g. ioprio_check_cap() takes an int as argument.
> With such implicit int casting function calls, the upper 16-bits of the
> int argument may be left uninitialized by the compiler, resulting in
> invalid values for the IOPRIO_PRIO_CLASS() macro (garbage upper bits)
> and in an error return for functions such as ioprio_check_cap().
> 
> Fix this by masking the result of the shift by IOPRIO_CLASS_SHIFT bits
> in the IOPRIO_PRIO_CLASS() macro. The new macro IOPRIO_CLASS_MASK
> defines the 3-bits mask for the priority class.
> 
> While at it, cleanup the following:
> * Apply the mask IOPRIO_PRIO_MASK to the data argument of the
>    IOPRIO_PRIO_VALUE() macro to ignore upper bits of the data value.
> * Remove unnecessary parenthesis around fixed values in the macro
>    definitions in include/uapi/linux/ioprio.h.
> * Update the outdated mention of CFQ in the comment describing priority
>    classes and instead mention BFQ and mq-deadline.
> * Change the argument name of the IOPRIO_PRIO_CLASS() and
>    IOPRIO_PRIO_DATA() macros from "mask" to "ioprio" to reflect the fact
>    that an IO priority value should be passed rather than a mask.
> * Change the ioprio_valid() macro into an inline function, adding a
>    check on the maximum value of the class of a priority value as
>    defined by the IOPRIO_CLASS_MAX enum value. Move this function to
>    the kernel side in include/linux/ioprio.h.
> * Remove the unnecessary "else" after the return statements in
>    task_nice_ioclass().
> 
> Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
> ---
>   include/linux/ioprio.h      | 15 ++++++++++++---
>   include/uapi/linux/ioprio.h | 19 +++++++++++--------
>   2 files changed, 23 insertions(+), 11 deletions(-)
> 
> diff --git a/include/linux/ioprio.h b/include/linux/ioprio.h
> index ef9ad4fb245f..9b3a6d8172b4 100644
> --- a/include/linux/ioprio.h
> +++ b/include/linux/ioprio.h
> @@ -8,6 +8,16 @@
>   
>   #include <uapi/linux/ioprio.h>
>   
> +/*
> + * Check that a priority value has a valid class.
> + */
> +static inline bool ioprio_valid(unsigned short ioprio)

Wouldn't it be better to use 'u16' here as type, as we're relying on the 
number of bits?

> +{
> +	unsigned short class = IOPRIO_PRIO_CLASS(ioprio);
> +
> +	return class > IOPRIO_CLASS_NONE && class < IOPRIO_CLASS_MAX;
> +}
> +
>   /*
>    * if process has set io priority explicitly, use that. if not, convert
>    * the cpu scheduler nice value to an io priority
> @@ -25,10 +35,9 @@ static inline int task_nice_ioclass(struct task_struct *task)
>   {
>   	if (task->policy == SCHED_IDLE)
>   		return IOPRIO_CLASS_IDLE;
> -	else if (task_is_realtime(task))
> +	if (task_is_realtime(task))
>   		return IOPRIO_CLASS_RT;
> -	else
> -		return IOPRIO_CLASS_BE;
> +	return IOPRIO_CLASS_BE;
>   }
>   
>   /*
> diff --git a/include/uapi/linux/ioprio.h b/include/uapi/linux/ioprio.h
> index 77b17e08b0da..abc40965aa96 100644
> --- a/include/uapi/linux/ioprio.h
> +++ b/include/uapi/linux/ioprio.h
> @@ -5,12 +5,15 @@
>   /*
>    * Gives us 8 prio classes with 13-bits of data for each class
>    */
> -#define IOPRIO_CLASS_SHIFT	(13)
> +#define IOPRIO_CLASS_SHIFT	13
> +#define IOPRIO_CLASS_MASK	0x07
>   #define IOPRIO_PRIO_MASK	((1UL << IOPRIO_CLASS_SHIFT) - 1)
>   
> -#define IOPRIO_PRIO_CLASS(mask)	((mask) >> IOPRIO_CLASS_SHIFT)
> -#define IOPRIO_PRIO_DATA(mask)	((mask) & IOPRIO_PRIO_MASK)
> -#define IOPRIO_PRIO_VALUE(class, data)	(((class) << IOPRIO_CLASS_SHIFT) | data)
> +#define IOPRIO_PRIO_CLASS(ioprio)	\
> +	(((ioprio) >> IOPRIO_CLASS_SHIFT) & IOPRIO_CLASS_MASK)
> +#define IOPRIO_PRIO_DATA(ioprio)	((ioprio) & IOPRIO_PRIO_MASK)
> +#define IOPRIO_PRIO_VALUE(class, data)	\
> +	(((class) << IOPRIO_CLASS_SHIFT) | ((data) & IOPRIO_PRIO_MASK))
>   
>   /*
>    * These are the io priority groups as implemented by CFQ. RT is the realtime
> @@ -23,14 +26,14 @@ enum {
>   	IOPRIO_CLASS_RT,
>   	IOPRIO_CLASS_BE,
>   	IOPRIO_CLASS_IDLE,
> -};
>   
> -#define ioprio_valid(mask)	(IOPRIO_PRIO_CLASS((mask)) != IOPRIO_CLASS_NONE)
> +	IOPRIO_CLASS_MAX,
> +};
>   
>   /*
>    * 8 best effort priority levels are supported
>    */
> -#define IOPRIO_BE_NR	(8)
> +#define IOPRIO_BE_NR	8
>   
>   enum {
>   	IOPRIO_WHO_PROCESS = 1,
> @@ -41,6 +44,6 @@ enum {
>   /*
>    * Fallback BE prioritye@su
>    */
> -#define IOPRIO_NORM	(4)
> +#define IOPRIO_NORM	4
>   
>   #endif /* _UAPI_LINUX_IOPRIO_H */
> 
Other than that:

Reviewed-by: Hannes Reinecke <hare@suse.de>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@suse.de                              +49 911 74053 688
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