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Commit 48e025e6 authored by Corrado Zoccolo's avatar Corrado Zoccolo Committed by Jens Axboe
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cfq-iosched: fix possible problem with jiffies wraparound 



The RR service tree is indexed by a key that is relative to current jiffies.
This can cause problems on jiffies wraparound.

The patch fixes it using time_before comparison, and changing
the add_front path to use a relative number, too.

Signed-off-by: default avatarCorrado Zoccolo <czoccolo@gmail.com>
Signed-off-by: default avatarJens Axboe <jens.axboe@oracle.com>
parent 30996f40

block/cfq-iosched.c

+6 −3
Original line number Diff line number Diff line
@@ -512,8 +512,11 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
		rb_key = cfq_slice_offset(cfqd, cfqq) + jiffies;

		rb_key += cfqq->slice_resid;

		cfqq->slice_resid = 0;

	} else

		rb_key = 0;

	} else {

		rb_key = -HZ;

		__cfqq = cfq_rb_first(&cfqd->service_tree);

		rb_key += __cfqq ? __cfqq->rb_key : jiffies;

	}



	if (!RB_EMPTY_NODE(&cfqq->rb_node)) {

		/*
@@ -547,7 +550,7 @@ static void cfq_service_tree_add(struct cfq_data *cfqd, struct cfq_queue *cfqq, 
			n = &(*p)->rb_left;

		else if (cfq_class_idle(cfqq) > cfq_class_idle(__cfqq))

			n = &(*p)->rb_right;

		else if (rb_key < __cfqq->rb_key)

		else if (time_before(rb_key, __cfqq->rb_key))

			n = &(*p)->rb_left;

		else

			n = &(*p)->rb_right;