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>

1 files changed, 2 insertions, 9 deletions

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index ebab60c6be9d..9c4b679908f4 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -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;
         }