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From: Paolo Valente <paolo.valente@linaro.org>
To: Jens Axboe <axboe@kernel.dk>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
	bfq-iosched@googlegroups.com, oleksandr@natalenko.name,
	patdung100@gmail.com, cevich@redhat.com,
	Paolo Valente <paolo.valente@linaro.org>
Subject: [PATCH BUGFIX 3/6] block, bfq: get extra ref to prevent a queue from being freed during a group move
Date: Fri, 31 Jan 2020 10:24:06 +0100	[thread overview]
Message-ID: <20200131092409.10867-4-paolo.valente@linaro.org> (raw)
In-Reply-To: <20200131092409.10867-1-paolo.valente@linaro.org>

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


  parent reply	other threads:[~2020-01-31  9:25 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-31  9:24 [PATCH BUGFIX 0/6] block, bfq: series of fixes, and not only, for some recently reported issues Paolo Valente
2020-01-31  9:24 ` [PATCH BUGFIX 1/6] block, bfq: do not plug I/O for bfq_queues with no proc refs Paolo Valente
2020-01-31  9:24 ` [PATCH BUGFIX 2/6] block, bfq: do not insert oom queue into position tree Paolo Valente
2020-01-31  9:24 ` Paolo Valente [this message]
2020-01-31 10:20   ` [PATCH BUGFIX 3/6] block, bfq: get extra ref to prevent a queue from being freed during a group move Oleksandr Natalenko
2020-01-31 10:41     ` Paolo Valente
2020-01-31  9:24 ` [PATCH BUGFIX 4/6] block, bfq: extend incomplete name of field on_st Paolo Valente
2020-01-31  9:24 ` [PATCH BUGFIX 5/6] block, bfq: get a ref to a group when adding it to a service tree Paolo Valente
2020-02-01  4:44   ` Jens Axboe
2020-01-31  9:24 ` [PATCH BUGFIX 6/6] block, bfq: clarify the goal of bfq_split_bfqq() Paolo Valente
2020-02-01  4:48 ` [PATCH BUGFIX 0/6] block, bfq: series of fixes, and not only, for some recently reported issues Jens Axboe
2020-02-03  8:50   ` Paolo Valente

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