From a13bd91be22318768d55470cbc0b0f4488ef9edf Mon Sep 17 00:00:00 2001 From: Yu Kuai Date: Fri, 14 Apr 2023 16:40:08 +0800 Subject: block/rq_qos: protect rq_qos apis with a new lock 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 Acked-by: Tejun Heo Link: https://lore.kernel.org/r/20230414084008.2085155-1-yukuai1@huaweicloud.com Signed-off-by: Jens Axboe --- block/blk-rq-qos.c | 20 ++++++-------------- 1 file changed, 6 insertions(+), 14 deletions(-) (limited to 'block/blk-rq-qos.c') diff --git a/block/blk-rq-qos.c b/block/blk-rq-qos.c index d8cc820a365e..167be74df4ee 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); -- cgit