[PATCH BUGFIX 0/2] block, bfq: fix two memory leaks related to cgroups

[PATCH BUGFIX 0/2] block, bfq: fix two memory leaks related to cgroups

[Paolo Valente]

Hi Jens,
these two patches fix two related memory leaks, the first reported in
[1], and the second found by ourselves while fixing the first.

Thanks,
Paolo

[1] https://www.mail-archive.com/linux-block@vger.kernel.org/msg16258.html

Paolo Valente (2):
  block, bfq: put async queues for root bfq groups too
  bfq-sq, bfq-mq: release oom-queue ref to root group on exit

 block/bfq-cgroup.c  | 7 +++++--
 block/bfq-iosched.c | 3 +++
 2 files changed, 8 insertions(+), 2 deletions(-)

--
2.15.1

[PATCH BUGFIX 1/2] block, bfq: put async queues for root bfq groups too

[Paolo Valente]

For each pair [device for which bfq is selected as I/O scheduler,
group in blkio/io], bfq maintains a corresponding bfq group. Each such
bfq group contains a set of async queues, with each async queue
created on demand, i.e., when some I/O request arrives for it.  On
creation, an async queue gets an extra reference, to make sure that
the queue is not freed as long as its bfq group exists.  Accordingly,
to allow the queue to be freed after the group exited, this extra
reference must released on group exit.

The above holds also for a bfq root group, i.e., for the bfq group
corresponding to the root blkio/io root for a given device. Yet, by
mistake, the references to the existing async queues of a root group
are not released when the latter exits. This causes a memory leak when
the instance of bfq for a given device exits. In a similar vein,
bfqg_stats_xfer_dead is not executed for a root group.

This commit fixes bfq_pd_offline so that the latter executes the above
missing operations for a root group too.

Reported-by: Holger Hoffstätte <holger@applied-asynchrony.com>
Reported-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Davide Ferrari <davideferrari8@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
 block/bfq-cgroup.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/block/bfq-cgroup.c b/block/bfq-cgroup.c
index da1525ec4c87..d819dc77fe65 100644
--- a/block/bfq-cgroup.c
+++ b/block/bfq-cgroup.c
@@ -775,10 +775,11 @@ static void bfq_pd_offline(struct blkg_policy_data *pd)
 	unsigned long flags;
 	int i;
 
+	spin_lock_irqsave(&bfqd->lock, flags);
+
 	if (!entity) /* root group */
-		return;
+		goto put_async_queues;
 
-	spin_lock_irqsave(&bfqd->lock, flags);
 	/*
 	 * Empty all service_trees belonging to this group before
 	 * deactivating the group itself.
@@ -809,6 +810,8 @@ static void bfq_pd_offline(struct blkg_policy_data *pd)
 	}
 
 	__bfq_deactivate_entity(entity, false);
+
+put_async_queues:
 	bfq_put_async_queues(bfqd, bfqg);
 
 	spin_unlock_irqrestore(&bfqd->lock, flags);
-- 
2.15.1

[PATCH BUGFIX 2/2] bfq-sq, bfq-mq: release oom-queue ref to root group on exit

[Paolo Valente]

On scheduler init, a reference to the root group, and a reference to
its corresponding blkg are taken for the oom queue. Yet these
references are not released on scheduler exit, which prevents these
objects from be freed. This commit adds the missing reference
releases.

Reported-by: Davide Ferrari <davideferrari8@gmail.com>
Signed-off-by: Paolo Valente <paolo.valente@linaro.org>
---
 block/bfq-iosched.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index ea48b5c8f088..c56a495af2e8 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -5015,6 +5015,9 @@ static void bfq_exit_queue(struct elevator_queue *e)
 
 	hrtimer_cancel(&bfqd->idle_slice_timer);
 
+	/* release oom-queue reference to root group */
+	bfqg_and_blkg_put(bfqd->root_group);
+
 #ifdef CONFIG_BFQ_GROUP_IOSCHED
 	blkcg_deactivate_policy(bfqd->queue, &blkcg_policy_bfq);
 #else
-- 
2.15.1

Re: [PATCH BUGFIX 0/2] block, bfq: fix two memory leaks related to cgroups

[Jens Axboe]

On Tue, Jan 09 2018, Paolo Valente wrote:
> Hi Jens,
> these two patches fix two related memory leaks, the first reported in
> [1], and the second found by ourselves while fixing the first.

Thanks, applied for 4.16, thanks.

-- 
Jens Axboe