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Subject[PATCH BUGFIX V2 3/7] block, bfq: get extra ref to prevent a queue from being freed during a group move
Date
In bfq_bfqq_move(), the bfq_queue, say Q, to be moved to a new group
may happen to be deactivated in the scheduling data structures of the
source group (and then activated in the destination group). If Q is
referred only by the data structures in the source group when the
deactivation happens, then Q is freed upon the deactivation.

This commit addresses this issue by getting an extra reference before
the possible deactivation, and releasing this extra reference after Q
has been moved.

Tested-by: Chris Evich <cevich@redhat.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
block/bfq-cgroup.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index e1419edde2ec..8ab7f18ff8cb 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -651,6 +651,12 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,
bfq_bfqq_expire(bfqd, bfqd->in_service_queue,
false, BFQQE_PREEMPTED);

+ /*
+ * get extra reference to prevent bfqq from being freed in
+ * next possible deactivate
+ */
+ bfqq->ref++;
+
if (bfq_bfqq_busy(bfqq))
bfq_deactivate_bfqq(bfqd, bfqq, false, false);
else if (entity->on_st)
@@ -670,6 +676,8 @@ void bfq_bfqq_move(struct bfq_data *bfqd, struct bfq_queue *bfqq,

if (!bfqd->in_service_queue && !bfqd->rq_in_driver)
bfq_schedule_dispatch(bfqd);
+ /* release extra ref taken above */
+ bfq_put_queue(bfqq);
}

/**
--
2.20.1
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