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cfq-iosched: don't delay async queue if it hasn't dispatched at all 

We cannot delay for the first dispatch of the async queue if it
hasn't dispatched at all, since that could present a local user
DoS attack vector using an app that just did slow timed sync reads
while filling memory.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Jens Axboe 2009-10-04 20:36:19 +02:00
parent ac481c20ef
commit e00c54c36a
1 changed files with 2 additions and 9 deletions
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11
block/cfq-iosched.c
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@ -1345,16 +1345,9 @@ static int cfq_dispatch_requests(struct request_queue *q, int force)
unsigned long last_sync = jiffies - cfqd->last_end_sync_rq;
unsigned int depth;
/*
* must wait a bit longer
*/
if (last_sync < cfqd->cfq_slice[1]) {
cfq_schedule_dispatch(cfqd,
cfqd->cfq_slice[1] - last_sync);
return 0;
}
depth = last_sync / cfqd->cfq_slice[1];
if (!depth && !cfqq->dispatched)
depth = 1;
if (depth < max_dispatch)
max_dispatch = depth;
}