Commit db599f9e authored Jun 25, 2019 by Paolo Valente Committed by Jens Axboe Jun 25, 2019

block, bfq: fix rq_in_driver check in bfq_update_inject_limit



One of the cases where the parameters for injection may be updated is
when there are no more in-flight I/O requests. The number of in-flight
requests is stored in the field bfqd->rq_in_driver of the descriptor
bfqd of the device. So, the controlled condition is
bfqd->rq_in_driver == 0.

Unfortunately, this is wrong because, the instruction that checks this
condition is in the code path that handles the completion of a
request, and, in particular, the instruction is executed before
bfqd->rq_in_driver is decremented in such a code path.

This commit fixes this issue by just replacing 0 with 1 in the
comparison.

Reported-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Tested-by: Srivatsa S. Bhat (VMware) <srivatsa@csail.mit.edu>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

parent 766d6141

block/bfq-iosched.c

+7 −1

Original line number	Diff line number	Diff line
		@@ -5481,8 +5481,14 @@ static void bfq_update_inject_limit(struct bfq_data *bfqd,
		* total service time, and there seem to be the right
		* conditions to do it, or we can lower the last base value
		* computed.
		*
		* NOTE: (bfqd->rq_in_driver == 1) means that there is no I/O
		* request in flight, because this function is in the code
		* path that handles the completion of a request of bfqq, and,
		* in particular, this function is executed before
		* bfqd->rq_in_driver is decremented in such a code path.
		*/
		if ((bfqq->last_serv_time_ns == 0 && bfqd->rq_in_driver == 0) \|\|
		if ((bfqq->last_serv_time_ns == 0 && bfqd->rq_in_driver == 1) \|\|
		tot_time_ns < bfqq->last_serv_time_ns) {
		bfqq->last_serv_time_ns = tot_time_ns;
		/*

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