[PATCH 3.17 085/141] block: Fix computation of merged request priority

From: Greg Kroah-Hartman
Date: Wed Nov 19 2014 - 17:19:30 EST

3.17-stable review patch. If anyone has any objections, please let me know.


From: Jan Kara <jack@xxxxxxx>

commit ece9c72accdc45c3a9484dacb1125ce572647288 upstream.

Priority of a merged request is computed by ioprio_best(). If one of the
requests has undefined priority (IOPRIO_CLASS_NONE) and another request
has priority from IOPRIO_CLASS_BE, the function will return the
undefined priority which is wrong. Fix the function to properly return
priority of a request with the defined priority.

Fixes: d58cdfb89ce0c6bd5f81ae931a984ef298dbda20
Signed-off-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Jeff Moyer <jmoyer@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

block/ioprio.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

--- a/block/ioprio.c
+++ b/block/ioprio.c
@@ -157,14 +157,16 @@ out:

int ioprio_best(unsigned short aprio, unsigned short bprio)
- unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
- unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
+ unsigned short aclass;
+ unsigned short bclass;

- if (aclass == IOPRIO_CLASS_NONE)
- aclass = IOPRIO_CLASS_BE;
- if (bclass == IOPRIO_CLASS_NONE)
- bclass = IOPRIO_CLASS_BE;
+ if (!ioprio_valid(aprio))
+ if (!ioprio_valid(bprio))

+ aclass = IOPRIO_PRIO_CLASS(aprio);
+ bclass = IOPRIO_PRIO_CLASS(bprio);
if (aclass == bclass)
return min(aprio, bprio);
if (aclass > bclass)

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