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Date: Sun, 23 Apr 2023 16:15:59 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: Yu Kuai <yukuai1@...weicloud.com>, tj@...nel.org, hch@....de,
josef@...icpanda.com, axboe@...nel.dk
Cc: cgroups@...r.kernel.org, linux-block@...r.kernel.org,
linux-kernel@...r.kernel.org, yi.zhang@...wei.com,
yangerkun@...wei.com, "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH for-6.4/block] block/rq_qos: protect rq_qos apis with a
new lock
Hi,
在 2023/04/14 16:40, Yu Kuai 写道:
> From: Yu Kuai <yukuai3@...wei.com>
>
> 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.
>
Friendly ping ...
Thanks,
Kuai
> Fixes: 50e34d78815e ("block: disable the elevator int del_gendisk")
> Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> ---
> 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 1c1ebeb51003..0d79d864ecb1 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -705,6 +705,13 @@ 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;
> @@ -849,6 +856,7 @@ 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);
> @@ -856,6 +864,7 @@ 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 269765d16cfd..fc7f902bdf5b 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 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);
> diff --git a/block/blk-wbt.c b/block/blk-wbt.c
> index e49a48684532..53bf5aa6f9ad 100644
> --- a/block/blk-wbt.c
> +++ b/block/blk-wbt.c
> @@ -942,7 +942,9 @@ 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 6ede578dfbc6..17774f55743e 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -395,6 +395,7 @@ 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;
>
>
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