On 8/6/21 8:57 AM, Damien Le Moal wrote:

On 2021/08/06 15:35, Hannes Reinecke wrote:

quoted

On 8/6/21 7:11 AM, Damien Le Moal wrote:

quoted

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* Update the outdated mention of CFQ in the comment describing priority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 <redacted>
---
  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?

Other functions in block/ioprio.c and in include/linux/ioprio.h use "unsigned
short", so I followed. But many functions, if not most, use "int". This is all a
bit of a mess. I think we need a "typedef ioprio_t u16;" to clean things up. But
there are a lot of places to fix. I can add such patch... Worth it ?

Possibly not.
Consider my comment retracted :-)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		           Kernel Storage Architect
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer