[PATCH 6.4 017/800] block/rq_qos: protect rq_qos apis with a new lock

Greg Kroah-Hartman
2023-07-16T19:53:35Z

From: Yu Kuai <yukuai3@huawei.com>

[ Upstream commit a13bd91be22318768d55470cbc0b0f4488ef9edf ]

commit 50e34d78815e ("block: disable the elevator int del_gendisk")
move rq_qos_exit() from disk_release() to del_gendisk(), this will
introduce some problems:

1) If rq_qos_add() is triggered by enabling iocost/iolatency through
cgroupfs, then it can concurrent with del_gendisk(), it's not safe to
write 'q->rq_qos' concurrently.

2) Activate cgroup policy that is relied on rq_qos will call
rq_qos_add() and blkcg_activate_policy(), and if rq_qos_exit() is
called in the middle, null-ptr-dereference will be triggered in
blkcg_activate_policy().

3) blkg_conf_open_bdev() can call blkdev_get_no_open() first to find the
disk, then if rq_qos_exit() from del_gendisk() is done before
rq_qos_add(), then memory will be leaked.

This patch add a new disk level mutex 'rq_qos_mutex':

1) The lock will protect rq_qos_exit() directly.

2) For wbt that doesn't relied on blk-cgroup, rq_qos_add() can only be
called from disk initialization for now because wbt can't be
destructed until rq_qos_exit(), so it's safe not to protect wbt for
now. Hoever, in case that rq_qos dynamically destruction is supported
in the furture, this patch also protect rq_qos_add() from wbt_init()
directly, this is enough because blk-sysfs already synchronize
writers with disk removal.

3) For iocost and iolatency, in order to synchronize disk removal and
cgroup configuration, the lock is held after blkdev_get_no_open()
from blkg_conf_open_bdev(), and is released in blkg_conf_exit().
In order to fix the above memory leak, disk_live() is checked after
holding the new lock.

Fixes: 50e34d78815e ("block: disable the elevator int del_gendisk")
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Link: https://lore.kernel.org/r/20230414084008.2085155-1-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-cgroup.c | 9 +++++++++
block/blk-core.c | 1 +
block/blk-rq-qos.c | 20 ++++++--------------
block/blk-wbt.c | 2 ++
include/linux/blkdev.h | 1 +
5 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index dce1548a7a0c3..5215bc7af5514 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -762,6 +762,13 @@ int blkg_conf_open_bdev(struct blkg_conf_ctx *ctx)
return -ENODEV;
}

+ mutex_lock(&bdev->bd_queue->rq_qos_mutex);
+ if (!disk_live(bdev->bd_disk)) {
+ blkdev_put_no_open(bdev);
+ mutex_unlock(&bdev->bd_queue->rq_qos_mutex);
+ return -ENODEV;
+ }
+
ctx->body = input;
ctx->bdev = bdev;
return 0;
@@ -906,6 +913,7 @@ EXPORT_SYMBOL_GPL(blkg_conf_prep);
*/
void blkg_conf_exit(struct blkg_conf_ctx *ctx)
__releases(&ctx->bdev->bd_queue->queue_lock)
+ __releases(&ctx->bdev->bd_queue->rq_qos_mutex)
{
if (ctx->blkg) {
spin_unlock_irq(&bdev_get_queue(ctx->bdev)->queue_lock);
@@ -913,6 +921,7 @@ void blkg_conf_exit(struct blkg_conf_ctx *ctx)
}

if (ctx->bdev) {
+ mutex_unlock(&ctx->bdev->bd_queue->rq_qos_mutex);
blkdev_put_no_open(ctx->bdev);
ctx->body = NULL;
ctx->bdev = NULL;
diff --git a/block/blk-core.c b/block/blk-core.c
index 1da77e7d62894..3fc68b9444791 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -420,6 +420,7 @@ struct request_queue *blk_alloc_queue(int node_id)
mutex_init(&q->debugfs_mutex);
mutex_init(&q->sysfs_lock);
mutex_init(&q->sysfs_dir_lock);
+ mutex_init(&q->rq_qos_mutex);
spin_lock_init(&q->queue_lock);

init_waitqueue_head(&q->mq_freeze_wq);
diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c
index d8cc820a365e3..167be74df4eec 100644
--- a/block/blk-rq-qos.c
+++ b/block/blk-rq-qos.c
@@ -288,11 +288,13 @@ void rq_qos_wait(struct rq_wait *rqw, void *private_data,

void rq_qos_exit(struct request_queue *q)
{
+ mutex_lock(&q->rq_qos_mutex);
while (q->rq_qos) {
struct rq_qos *rqos = q->rq_qos;
q->rq_qos = rqos->next;
rqos->ops->exit(rqos);
}
+ mutex_unlock(&q->rq_qos_mutex);
}

int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
@@ -300,6 +302,8 @@ int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
{
struct request_queue *q = disk->queue;

+ lockdep_assert_held(&q->rq_qos_mutex);
+
rqos->disk = disk;
rqos->id = id;
rqos->ops = ops;
@@ -307,18 +311,13 @@ int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,
/*
* No IO can be in-flight when adding rqos, so freeze queue, which
* is fine since we only support rq_qos for blk-mq queue.
- *
- * Reuse ->queue_lock for protecting against other concurrent
- * rq_qos adding/deleting
*/
blk_mq_freeze_queue(q);

- spin_lock_irq(&q->queue_lock);
if (rq_qos_id(q, rqos->id))
goto ebusy;
rqos->next = q->rq_qos;
q->rq_qos = rqos;
- spin_unlock_irq(&q->queue_lock);

blk_mq_unfreeze_queue(q);

@@ -330,7 +329,6 @@ int rq_qos_add(struct rq_qos *rqos, struct gendisk *disk, enum rq_qos_id id,

return 0;
ebusy:
- spin_unlock_irq(&q->queue_lock);
blk_mq_unfreeze_queue(q);
return -EBUSY;
}
@@ -340,21 +338,15 @@ void rq_qos_del(struct rq_qos *rqos)
struct request_queue *q = rqos->disk->queue;
struct rq_qos **cur;

- /*
- * See comment in rq_qos_add() about freezing queue & using
- * ->queue_lock.
- */
- blk_mq_freeze_queue(q);
+ lockdep_assert_held(&q->rq_qos_mutex);

- spin_lock_irq(&q->queue_lock);
+ blk_mq_freeze_queue(q);
for (cur = &q->rq_qos; *cur; cur = &(*cur)->next) {
if (*cur == rqos) {
*cur = rqos->next;
break;
}
}
- spin_unlock_irq(&q->queue_lock);
-
blk_mq_unfreeze_queue(q);

mutex_lock(&q->debugfs_mutex);
diff --git a/block/blk-wbt.c b/block/blk-wbt.c
index 9ec2a2f1eda38..7a87506ff8e1c 100644
--- a/block/blk-wbt.c
+++ b/block/blk-wbt.c
@@ -944,7 +944,9 @@ int wbt_init(struct gendisk *disk)
/*
* Assign rwb and add the stats callback.
*/
+ mutex_lock(&q->rq_qos_mutex);
ret = rq_qos_add(&rwb->rqos, disk, RQ_QOS_WBT, &wbt_rqos_ops);
+ mutex_unlock(&q->rq_qos_mutex);
if (ret)
goto err_free;

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index be9d7d8237b33..67e942d776bd8 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -392,6 +392,7 @@ struct request_queue {

struct blk_queue_stats *stats;
struct rq_qos *rq_qos;
+ struct mutex rq_qos_mutex;

const struct blk_mq_ops *mq_ops;

--
2.39.2