[PATCH 3.10 30/70] block: Fix computation of merged request priority

Greg Kroah-Hartman
2014-11-19T21:30:46Z

From: Jan Kara <jack@suse.cz>

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@suse.cz>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/fs/ioprio.c
+++ b/fs/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))
+ aprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);
+ if (!ioprio_valid(bprio))
+ bprio = IOPRIO_PRIO_VALUE(IOPRIO_CLASS_BE, IOPRIO_NORM);

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