block: fix IOPRIO_PRIO_CLASS() and IOPRIO_PRIO_VALUE() macros

The ki_ioprio field of struct kiocb 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. Similarly, apply the IOPRIO_PRIO_MASK mask to the data argument of the IOPRIO_PRIO_VALUE() macro to ignore the upper bits of the data value. The IOPRIO_CLASS_MASK mask is also applied to the class argument of this macro before shifting the result by IOPRIO_CLASS_SHIFT bits. While at it, also change the argument name of the IOPRIO_PRIO_CLASS() and IOPRIO_PRIO_DATA() macros from "mask" to "ioprio" to reflect the fact that a priority value should be passed rather than a mask.

DLDamien Le Moal committed 5 years ago