From: Vasily Tarasov Date: Thu, 12 Oct 2006 13:09:51 +0000 (+0200) Subject: [PATCH] block layer: ioprio_best function fix X-Git-Tag: v2.6.19-rc2~16^2 X-Git-Url: http://pilppa.com/gitweb/?a=commitdiff_plain;h=d58cdfb89ce0c6bd5f81ae931a984ef298dbda20;p=linux-2.6-omap-h63xx.git [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: Vasily Tarasov Signed-off-by: Jens Axboe --- diff --git a/fs/ioprio.c b/fs/ioprio.c index 6dc6721d9e8..89e8da112a7 100644 --- a/fs/ioprio.c +++ b/fs/ioprio.c @@ -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)