Commit d58cdfb8 authored by Vasily Tarasov's avatar Vasily Tarasov Committed by Jens Axboe

[PATCH] block layer: ioprio_best function fix

Currently ioprio_best function first checks wethere aioprio or bioprio equals
IOPRIO_CLASS_NONE (ioprio_valid() macros does that) and if it is so it returns
bioprio/aioprio appropriately. Thus the next four lines, that set aclass/bclass
to IOPRIO_CLASS_BE, if aclass/bclass == IOPRIO_CLASS_NONE, are never executed.

The second problem: if aioprio from class IOPRIO_CLASS_NONE and bioprio from
class IOPRIO_CLASS_IDLE are passed to ioprio_best function, it will return
IOPRIO_CLASS_IDLE. It means that during __make_request we can merge two
requests and set the priority of merged request to IDLE, while one of
the initial requests originates from a process with NONE (default) priority.
So we can get a situation when a process with default ioprio will experience
IO starvation, while there is no process from real-time class in the system.

Just removing ioprio_valid check should correct situation.
Signed-off-by: default avatarVasily Tarasov <vtaras@openvz.org>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent cea2885a
......@@ -150,11 +150,6 @@ int ioprio_best(unsigned short aprio, unsigned short bprio)
unsigned short aclass = IOPRIO_PRIO_CLASS(aprio);
unsigned short bclass = IOPRIO_PRIO_CLASS(bprio);
if (!ioprio_valid(aprio))
return bprio;
if (!ioprio_valid(bprio))
return aprio;
if (aclass == IOPRIO_CLASS_NONE)
aclass = IOPRIO_CLASS_BE;
if (bclass == IOPRIO_CLASS_NONE)
......
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