block: Fix computation of merged request priority

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
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 8 insertions, 6 deletions

diff --git a/block/ioprio.c b/block/ioprio.c
index e50170ca7c33..31666c92b46a 100644
--- 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))
+                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)