Re: [PATCH 25/45] block: simplify bdev/disk lookup in blkdev_get

From: Jan Kara <jack@suse.cz>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, Tejun Heo <tj@kernel.org>,
	Josef Bacik <josef@toxicpanda.com>, Coly Li <colyli@suse.de>,
	Mike Snitzer <snitzer@redhat.com>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jan Kara <jack@suse.cz>,
	Johannes Thumshirn <johannes.thumshirn@wdc.com>,
	dm-devel@redhat.com, Jan Kara <jack@suse.com>,
	linux-block@vger.kernel.org, linux-bcache@vger.kernel.org,
	linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 25/45] block: simplify bdev/disk lookup in blkdev_get
Date: Mon, 30 Nov 2020 10:24:28 +0100	[thread overview]
Message-ID: <20201130092428.GC11250@quack2.suse.cz> (raw)
In-Reply-To: <20201128161510.347752-26-hch@lst.de>

On Sat 28-11-20 17:14:50, Christoph Hellwig wrote:
> To simplify block device lookup and a few other upcoming areas, make sure
> that we always have a struct block_device available for each disk and
> each partition, and only find existing block devices in bdget.  The only
> downside of this is that each device and partition uses a little more
> memory.  The upside will be that a lot of code can be simplified.
> 
> With that all we need to look up the block device is to lookup the inode
> and do a few sanity checks on the gendisk, instead of the separate lookup
> for the gendisk.  For blk-cgroup which wants to access a gendisk without
> opening it, a new blkdev_{get,put}_no_open low-level interface is added
> to replace the previous get_gendisk use.
> 
> Note that the change to look up block device directly instead of the two
> step lookup using struct gendisk causes a subtile change in behavior:
> accessing a non-existing partition on an existing block device can now
> cause a call to request_module.  That call is harmless, and in practice
> no recent system will access these nodes as they aren't created by udev
> and static /dev/ setups are unusual.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>

Looks good to me! You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

									Honza

> ---
>  block/blk-cgroup.c         |  42 ++++----
>  block/blk-iocost.c         |  36 +++----
>  block/blk.h                |   2 +-
>  block/genhd.c              | 210 +++++--------------------------------
>  block/partitions/core.c    |  29 ++---
>  fs/block_dev.c             | 177 +++++++++++++++++--------------
>  include/linux/blk-cgroup.h |   4 +-
>  include/linux/blkdev.h     |   6 ++
>  include/linux/genhd.h      |   7 +-
>  9 files changed, 194 insertions(+), 319 deletions(-)
> 
> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
> index 54fbe1e80cc41a..19650eb42b9f00 100644
> --- a/block/blk-cgroup.c
> +++ b/block/blk-cgroup.c
> @@ -556,22 +556,22 @@ static struct blkcg_gq *blkg_lookup_check(struct blkcg *blkcg,
>  }
>  
>  /**
> - * blkg_conf_prep - parse and prepare for per-blkg config update
> + * blkcg_conf_open_bdev - parse and open bdev for per-blkg config update
>   * @inputp: input string pointer
>   *
>   * Parse the device node prefix part, MAJ:MIN, of per-blkg config update
> - * from @input and get and return the matching gendisk.  *@inputp is
> + * from @input and get and return the matching bdev.  *@inputp is
>   * updated to point past the device node prefix.  Returns an ERR_PTR()
>   * value on error.
>   *
>   * Use this function iff blkg_conf_prep() can't be used for some reason.
>   */
> -struct gendisk *blkcg_conf_get_disk(char **inputp)
> +struct block_device *blkcg_conf_open_bdev(char **inputp)
>  {
>  	char *input = *inputp;
>  	unsigned int major, minor;
> -	struct gendisk *disk;
> -	int key_len, part;
> +	struct block_device *bdev;
> +	int key_len;
>  
>  	if (sscanf(input, "%u:%u%n", &major, &minor, &key_len) != 2)
>  		return ERR_PTR(-EINVAL);
> @@ -581,16 +581,16 @@ struct gendisk *blkcg_conf_get_disk(char **inputp)
>  		return ERR_PTR(-EINVAL);
>  	input = skip_spaces(input);
>  
> -	disk = get_gendisk(MKDEV(major, minor), &part);
> -	if (!disk)
> +	bdev = blkdev_get_no_open(MKDEV(major, minor));
> +	if (!bdev)
>  		return ERR_PTR(-ENODEV);
> -	if (part) {
> -		put_disk_and_module(disk);
> +	if (bdev_is_partition(bdev)) {
> +		blkdev_put_no_open(bdev);
>  		return ERR_PTR(-ENODEV);
>  	}
>  
>  	*inputp = input;
> -	return disk;
> +	return bdev;
>  }
>  
>  /**
> @@ -607,18 +607,18 @@ struct gendisk *blkcg_conf_get_disk(char **inputp)
>   */
>  int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
>  		   char *input, struct blkg_conf_ctx *ctx)
> -	__acquires(rcu) __acquires(&disk->queue->queue_lock)
> +	__acquires(rcu) __acquires(&bdev->bd_disk->queue->queue_lock)
>  {
> -	struct gendisk *disk;
> +	struct block_device *bdev;
>  	struct request_queue *q;
>  	struct blkcg_gq *blkg;
>  	int ret;
>  
> -	disk = blkcg_conf_get_disk(&input);
> -	if (IS_ERR(disk))
> -		return PTR_ERR(disk);
> +	bdev = blkcg_conf_open_bdev(&input);
> +	if (IS_ERR(bdev))
> +		return PTR_ERR(bdev);
>  
> -	q = disk->queue;
> +	q = bdev->bd_disk->queue;
>  
>  	rcu_read_lock();
>  	spin_lock_irq(&q->queue_lock);
> @@ -689,7 +689,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
>  			goto success;
>  	}
>  success:
> -	ctx->disk = disk;
> +	ctx->bdev = bdev;
>  	ctx->blkg = blkg;
>  	ctx->body = input;
>  	return 0;
> @@ -700,7 +700,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
>  	spin_unlock_irq(&q->queue_lock);
>  	rcu_read_unlock();
>  fail:
> -	put_disk_and_module(disk);
> +	blkdev_put_no_open(bdev);
>  	/*
>  	 * If queue was bypassing, we should retry.  Do so after a
>  	 * short msleep().  It isn't strictly necessary but queue
> @@ -723,11 +723,11 @@ EXPORT_SYMBOL_GPL(blkg_conf_prep);
>   * with blkg_conf_prep().
>   */
>  void blkg_conf_finish(struct blkg_conf_ctx *ctx)
> -	__releases(&ctx->disk->queue->queue_lock) __releases(rcu)
> +	__releases(&ctx->bdev->bd_disk->queue->queue_lock) __releases(rcu)
>  {
> -	spin_unlock_irq(&ctx->disk->queue->queue_lock);
> +	spin_unlock_irq(&ctx->bdev->bd_disk->queue->queue_lock);
>  	rcu_read_unlock();
> -	put_disk_and_module(ctx->disk);
> +	blkdev_put_no_open(ctx->bdev);
>  }
>  EXPORT_SYMBOL_GPL(blkg_conf_finish);
>  
> diff --git a/block/blk-iocost.c b/block/blk-iocost.c
> index bbe86d1199dc5b..8e20fe4bddecf7 100644
> --- a/block/blk-iocost.c
> +++ b/block/blk-iocost.c
> @@ -3120,23 +3120,23 @@ static const match_table_t qos_tokens = {
>  static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
>  			     size_t nbytes, loff_t off)
>  {
> -	struct gendisk *disk;
> +	struct block_device *bdev;
>  	struct ioc *ioc;
>  	u32 qos[NR_QOS_PARAMS];
>  	bool enable, user;
>  	char *p;
>  	int ret;
>  
> -	disk = blkcg_conf_get_disk(&input);
> -	if (IS_ERR(disk))
> -		return PTR_ERR(disk);
> +	bdev = blkcg_conf_open_bdev(&input);
> +	if (IS_ERR(bdev))
> +		return PTR_ERR(bdev);
>  
> -	ioc = q_to_ioc(disk->queue);
> +	ioc = q_to_ioc(bdev->bd_disk->queue);
>  	if (!ioc) {
> -		ret = blk_iocost_init(disk->queue);
> +		ret = blk_iocost_init(bdev->bd_disk->queue);
>  		if (ret)
>  			goto err;
> -		ioc = q_to_ioc(disk->queue);
> +		ioc = q_to_ioc(bdev->bd_disk->queue);
>  	}
>  
>  	spin_lock_irq(&ioc->lock);
> @@ -3231,12 +3231,12 @@ static ssize_t ioc_qos_write(struct kernfs_open_file *of, char *input,
>  	ioc_refresh_params(ioc, true);
>  	spin_unlock_irq(&ioc->lock);
>  
> -	put_disk_and_module(disk);
> +	blkdev_put_no_open(bdev);
>  	return nbytes;
>  einval:
>  	ret = -EINVAL;
>  err:
> -	put_disk_and_module(disk);
> +	blkdev_put_no_open(bdev);
>  	return ret;
>  }
>  
> @@ -3287,23 +3287,23 @@ static const match_table_t i_lcoef_tokens = {
>  static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
>  				    size_t nbytes, loff_t off)
>  {
> -	struct gendisk *disk;
> +	struct block_device *bdev;
>  	struct ioc *ioc;
>  	u64 u[NR_I_LCOEFS];
>  	bool user;
>  	char *p;
>  	int ret;
>  
> -	disk = blkcg_conf_get_disk(&input);
> -	if (IS_ERR(disk))
> -		return PTR_ERR(disk);
> +	bdev = blkcg_conf_open_bdev(&input);
> +	if (IS_ERR(bdev))
> +		return PTR_ERR(bdev);
>  
> -	ioc = q_to_ioc(disk->queue);
> +	ioc = q_to_ioc(bdev->bd_disk->queue);
>  	if (!ioc) {
> -		ret = blk_iocost_init(disk->queue);
> +		ret = blk_iocost_init(bdev->bd_disk->queue);
>  		if (ret)
>  			goto err;
> -		ioc = q_to_ioc(disk->queue);
> +		ioc = q_to_ioc(bdev->bd_disk->queue);
>  	}
>  
>  	spin_lock_irq(&ioc->lock);
> @@ -3356,13 +3356,13 @@ static ssize_t ioc_cost_model_write(struct kernfs_open_file *of, char *input,
>  	ioc_refresh_params(ioc, true);
>  	spin_unlock_irq(&ioc->lock);
>  
> -	put_disk_and_module(disk);
> +	blkdev_put_no_open(bdev);
>  	return nbytes;
>  
>  einval:
>  	ret = -EINVAL;
>  err:
> -	put_disk_and_module(disk);
> +	blkdev_put_no_open(bdev);
>  	return ret;
>  }
>  
> diff --git a/block/blk.h b/block/blk.h
> index dfab98465db9a5..c4839abcfa27eb 100644
> --- a/block/blk.h
> +++ b/block/blk.h
> @@ -352,7 +352,6 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector);
>  
>  int blk_alloc_devt(struct hd_struct *part, dev_t *devt);
>  void blk_free_devt(dev_t devt);
> -void blk_invalidate_devt(dev_t devt);
>  char *disk_name(struct gendisk *hd, int partno, char *buf);
>  #define ADDPART_FLAG_NONE	0
>  #define ADDPART_FLAG_RAID	1
> @@ -384,6 +383,7 @@ static inline void hd_free_part(struct hd_struct *part)
>  {
>  	free_percpu(part->dkstats);
>  	kfree(part->info);
> +	bdput(part->bdev);
>  	percpu_ref_exit(&part->ref);
>  }
>  
> diff --git a/block/genhd.c b/block/genhd.c
> index f46e89226fdf91..bf8fa82f135f4e 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -27,17 +27,11 @@
>  
>  static struct kobject *block_depr;
>  
> -static DEFINE_XARRAY(bdev_map);
> -static DEFINE_MUTEX(bdev_map_lock);
> +DECLARE_RWSEM(bdev_lookup_sem);
>  
>  /* for extended dynamic devt allocation, currently only one major is used */
>  #define NR_EXT_DEVT		(1 << MINORBITS)
> -
> -/* For extended devt allocation.  ext_devt_lock prevents look up
> - * results from going away underneath its user.
> - */
> -static DEFINE_SPINLOCK(ext_devt_lock);
> -static DEFINE_IDR(ext_devt_idr);
> +static DEFINE_IDA(ext_devt_ida);
>  
>  static void disk_check_events(struct disk_events *ev,
>  			      unsigned int *clearing_ptr);
> @@ -580,14 +574,7 @@ int blk_alloc_devt(struct hd_struct *part, dev_t *devt)
>  		return 0;
>  	}
>  
> -	/* allocate ext devt */
> -	idr_preload(GFP_KERNEL);
> -
> -	spin_lock_bh(&ext_devt_lock);
> -	idx = idr_alloc(&ext_devt_idr, part, 0, NR_EXT_DEVT, GFP_NOWAIT);
> -	spin_unlock_bh(&ext_devt_lock);
> -
> -	idr_preload_end();
> +	idx = ida_alloc_range(&ext_devt_ida, 0, NR_EXT_DEVT, GFP_KERNEL);
>  	if (idx < 0)
>  		return idx == -ENOSPC ? -EBUSY : idx;
>  
> @@ -606,26 +593,8 @@ int blk_alloc_devt(struct hd_struct *part, dev_t *devt)
>   */
>  void blk_free_devt(dev_t devt)
>  {
> -	if (devt == MKDEV(0, 0))
> -		return;
> -
> -	if (MAJOR(devt) == BLOCK_EXT_MAJOR) {
> -		spin_lock_bh(&ext_devt_lock);
> -		idr_remove(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
> -		spin_unlock_bh(&ext_devt_lock);
> -	}
> -}
> -
> -/*
> - * We invalidate devt by assigning NULL pointer for devt in idr.
> - */
> -void blk_invalidate_devt(dev_t devt)
> -{
> -	if (MAJOR(devt) == BLOCK_EXT_MAJOR) {
> -		spin_lock_bh(&ext_devt_lock);
> -		idr_replace(&ext_devt_idr, NULL, blk_mangle_minor(MINOR(devt)));
> -		spin_unlock_bh(&ext_devt_lock);
> -	}
> +	if (MAJOR(devt) == BLOCK_EXT_MAJOR)
> +		ida_free(&ext_devt_ida, blk_mangle_minor(MINOR(devt)));
>  }
>  
>  static char *bdevt_str(dev_t devt, char *buf)
> @@ -640,28 +609,6 @@ static char *bdevt_str(dev_t devt, char *buf)
>  	return buf;
>  }
>  
> -static void blk_register_region(struct gendisk *disk)
> -{
> -	int i;
> -
> -	mutex_lock(&bdev_map_lock);
> -	for (i = 0; i < disk->minors; i++) {
> -		if (xa_insert(&bdev_map, disk_devt(disk) + i, disk, GFP_KERNEL))
> -			WARN_ON_ONCE(1);
> -	}
> -	mutex_unlock(&bdev_map_lock);
> -}
> -
> -static void blk_unregister_region(struct gendisk *disk)
> -{
> -	int i;
> -
> -	mutex_lock(&bdev_map_lock);
> -	for (i = 0; i < disk->minors; i++)
> -		xa_erase(&bdev_map, disk_devt(disk) + i);
> -	mutex_unlock(&bdev_map_lock);
> -}
> -
>  static void disk_scan_partitions(struct gendisk *disk)
>  {
>  	struct block_device *bdev;
> @@ -805,7 +752,7 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
>  		ret = bdi_register(bdi, "%u:%u", MAJOR(devt), MINOR(devt));
>  		WARN_ON(ret);
>  		bdi_set_owner(bdi, dev);
> -		blk_register_region(disk);
> +		bdev_add(disk->part0.bdev, devt);
>  	}
>  	register_disk(parent, disk, groups);
>  	if (register_queue)
> @@ -847,8 +794,8 @@ static void invalidate_partition(struct gendisk *disk, int partno)
>  	__invalidate_device(bdev, true);
>  
>  	/*
> -	 * Unhash the bdev inode for this device so that it gets evicted as soon
> -	 * as last inode reference is dropped.
> +	 * Unhash the bdev inode for this device so that it can't be looked
> +	 * up any more even if openers still hold references to it.
>  	 */
>  	remove_inode_hash(bdev->bd_inode);
>  	bdput(bdev);
> @@ -890,7 +837,8 @@ void del_gendisk(struct gendisk *disk)
>  	 * Block lookups of the disk until all bdevs are unhashed and the
>  	 * disk is marked as dead (GENHD_FL_UP cleared).
>  	 */
> -	down_write(&disk->lookup_sem);
> +	down_write(&bdev_lookup_sem);
> +
>  	/* invalidate stuff */
>  	disk_part_iter_init(&piter, disk,
>  			     DISK_PITER_INCL_EMPTY | DISK_PITER_REVERSE);
> @@ -903,7 +851,7 @@ void del_gendisk(struct gendisk *disk)
>  	invalidate_partition(disk, 0);
>  	set_capacity(disk, 0);
>  	disk->flags &= ~GENHD_FL_UP;
> -	up_write(&disk->lookup_sem);
> +	up_write(&bdev_lookup_sem);
>  
>  	if (!(disk->flags & GENHD_FL_HIDDEN)) {
>  		sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
> @@ -916,16 +864,6 @@ void del_gendisk(struct gendisk *disk)
>  	}
>  
>  	blk_unregister_queue(disk);
> -	
> -	if (!(disk->flags & GENHD_FL_HIDDEN))
> -		blk_unregister_region(disk);
> -	/*
> -	 * Remove gendisk pointer from idr so that it cannot be looked up
> -	 * while RCU period before freeing gendisk is running to prevent
> -	 * use-after-free issues. Note that the device number stays
> -	 * "in-use" until we really free the gendisk.
> -	 */
> -	blk_invalidate_devt(disk_devt(disk));
>  
>  	kobject_put(disk->part0.holder_dir);
>  	kobject_put(disk->slave_dir);
> @@ -964,7 +902,7 @@ static ssize_t disk_badblocks_store(struct device *dev,
>  	return badblocks_store(disk->bb, page, len, 0);
>  }
>  
> -static void request_gendisk_module(dev_t devt)
> +void blk_request_module(dev_t devt)
>  {
>  	unsigned int major = MAJOR(devt);
>  	struct blk_major_name **n;
> @@ -984,84 +922,6 @@ static void request_gendisk_module(dev_t devt)
>  		request_module("block-major-%d", MAJOR(devt));
>  }
>  
> -static bool get_disk_and_module(struct gendisk *disk)
> -{
> -	struct module *owner;
> -
> -	if (!disk->fops)
> -		return false;
> -	owner = disk->fops->owner;
> -	if (owner && !try_module_get(owner))
> -		return false;
> -	if (!kobject_get_unless_zero(&disk_to_dev(disk)->kobj)) {
> -		module_put(owner);
> -		return false;
> -	}
> -	return true;
> -
> -}
> -
> -/**
> - * get_gendisk - get partitioning information for a given device
> - * @devt: device to get partitioning information for
> - * @partno: returned partition index
> - *
> - * This function gets the structure containing partitioning
> - * information for the given device @devt.
> - *
> - * Context: can sleep
> - */
> -struct gendisk *get_gendisk(dev_t devt, int *partno)
> -{
> -	struct gendisk *disk = NULL;
> -
> -	might_sleep();
> -
> -	if (MAJOR(devt) != BLOCK_EXT_MAJOR) {
> -		mutex_lock(&bdev_map_lock);
> -		disk = xa_load(&bdev_map, devt);
> -		if (!disk) {
> -			mutex_unlock(&bdev_map_lock);
> -			request_gendisk_module(devt);
> -			mutex_lock(&bdev_map_lock);
> -			disk = xa_load(&bdev_map, devt);
> -		}
> -		if (disk && !get_disk_and_module(disk))
> -			disk = NULL;
> -		if (disk)
> -			*partno = devt - disk_devt(disk);
> -		mutex_unlock(&bdev_map_lock);
> -	} else {
> -		struct hd_struct *part;
> -
> -		spin_lock_bh(&ext_devt_lock);
> -		part = idr_find(&ext_devt_idr, blk_mangle_minor(MINOR(devt)));
> -		if (part && get_disk_and_module(part_to_disk(part))) {
> -			*partno = part->partno;
> -			disk = part_to_disk(part);
> -		}
> -		spin_unlock_bh(&ext_devt_lock);
> -	}
> -
> -	if (!disk)
> -		return NULL;
> -
> -	/*
> -	 * Synchronize with del_gendisk() to not return disk that is being
> -	 * destroyed.
> -	 */
> -	down_read(&disk->lookup_sem);
> -	if (unlikely((disk->flags & GENHD_FL_HIDDEN) ||
> -		     !(disk->flags & GENHD_FL_UP))) {
> -		up_read(&disk->lookup_sem);
> -		put_disk_and_module(disk);
> -		disk = NULL;
> -	} else {
> -		up_read(&disk->lookup_sem);
> -	}
> -	return disk;
> -}
> -
>  /**
>   * bdget_disk - do bdget() by gendisk and partition number
>   * @disk: gendisk of interest
> @@ -1559,11 +1419,6 @@ int disk_expand_part_tbl(struct gendisk *disk, int partno)
>   *
>   * This function releases all allocated resources of the gendisk.
>   *
> - * The struct gendisk refcount is incremented with get_gendisk() or
> - * get_disk_and_module(), and its refcount is decremented with
> - * put_disk_and_module() or put_disk(). Once the refcount reaches 0 this
> - * function is called.
> - *
>   * Drivers which used __device_add_disk() have a gendisk with a request_queue
>   * assigned. Since the request_queue sits on top of the gendisk for these
>   * drivers we also call blk_put_queue() for them, and we expect the
> @@ -1748,16 +1603,17 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
>  	if (!disk)
>  		return NULL;
>  
> +	disk->part0.bdev = bdev_alloc(disk, 0);
> +	if (!disk->part0.bdev)
> +		goto out_free_disk;
> +
>  	disk->part0.dkstats = alloc_percpu(struct disk_stats);
>  	if (!disk->part0.dkstats)
> -		goto out_free_disk;
> +		goto out_bdput;
>  
> -	init_rwsem(&disk->lookup_sem);
>  	disk->node_id = node_id;
> -	if (disk_expand_part_tbl(disk, 0)) {
> -		free_percpu(disk->part0.dkstats);
> -		goto out_free_disk;
> -	}
> +	if (disk_expand_part_tbl(disk, 0))
> +		goto out_free_bdstats;
>  
>  	ptbl = rcu_dereference_protected(disk->part_tbl, 1);
>  	rcu_assign_pointer(ptbl->part[0], &disk->part0);
> @@ -1773,7 +1629,7 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
>  	 */
>  	hd_sects_seq_init(&disk->part0);
>  	if (hd_ref_init(&disk->part0))
> -		goto out_free_part0;
> +		goto out_free_bdstats;
>  
>  	disk->minors = minors;
>  	rand_initialize_disk(disk);
> @@ -1782,8 +1638,10 @@ struct gendisk *__alloc_disk_node(int minors, int node_id)
>  	device_initialize(disk_to_dev(disk));
>  	return disk;
>  
> -out_free_part0:
> -	hd_free_part(&disk->part0);
> +out_free_bdstats:
> +	free_percpu(disk->part0.dkstats);
> +out_bdput:
> +	bdput(disk->part0.bdev);
>  out_free_disk:
>  	kfree(disk);
>  	return NULL;
> @@ -1807,26 +1665,6 @@ void put_disk(struct gendisk *disk)
>  }
>  EXPORT_SYMBOL(put_disk);
>  
> -/**
> - * put_disk_and_module - decrements the module and gendisk refcount
> - * @disk: the struct gendisk to decrement the refcount for
> - *
> - * This is a counterpart of get_disk_and_module() and thus also of
> - * get_gendisk().
> - *
> - * Context: Any context, but the last reference must not be dropped from
> - *          atomic context.
> - */
> -void put_disk_and_module(struct gendisk *disk)
> -{
> -	if (disk) {
> -		struct module *owner = disk->fops->owner;
> -
> -		put_disk(disk);
> -		module_put(owner);
> -	}
> -}
> -
>  static void set_disk_ro_uevent(struct gendisk *gd, int ro)
>  {
>  	char event[] = "DISK_RO=1";
> diff --git a/block/partitions/core.c b/block/partitions/core.c
> index a02e224115943d..696bd9ff63c64a 100644
> --- a/block/partitions/core.c
> +++ b/block/partitions/core.c
> @@ -340,12 +340,11 @@ void delete_partition(struct hd_struct *part)
>  	device_del(part_to_dev(part));
>  
>  	/*
> -	 * Remove gendisk pointer from idr so that it cannot be looked up
> -	 * while RCU period before freeing gendisk is running to prevent
> -	 * use-after-free issues. Note that the device number stays
> -	 * "in-use" until we really free the gendisk.
> +	 * Remove the block device from the inode hash, so that it cannot be
> +	 * looked up any more even when openers still hold references.
>  	 */
> -	blk_invalidate_devt(part_devt(part));
> +	remove_inode_hash(part->bdev->bd_inode);
> +
>  	percpu_ref_kill(&part->ref);
>  }
>  
> @@ -368,6 +367,7 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	dev_t devt = MKDEV(0, 0);
>  	struct device *ddev = disk_to_dev(disk);
>  	struct device *pdev;
> +	struct block_device *bdev;
>  	struct disk_part_tbl *ptbl;
>  	const char *dname;
>  	int err;
> @@ -402,11 +402,15 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	if (!p)
>  		return ERR_PTR(-EBUSY);
>  
> +	err = -ENOMEM;
>  	p->dkstats = alloc_percpu(struct disk_stats);
> -	if (!p->dkstats) {
> -		err = -ENOMEM;
> +	if (!p->dkstats)
>  		goto out_free;
> -	}
> +
> +	bdev = bdev_alloc(disk, partno);
> +	if (!bdev)
> +		goto out_free_stats;
> +	p->bdev = bdev;
>  
>  	hd_sects_seq_init(p);
>  	pdev = part_to_dev(p);
> @@ -420,10 +424,8 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  		struct partition_meta_info *pinfo;
>  
>  		pinfo = kzalloc_node(sizeof(*pinfo), GFP_KERNEL, disk->node_id);
> -		if (!pinfo) {
> -			err = -ENOMEM;
> -			goto out_free_stats;
> -		}
> +		if (!pinfo)
> +			goto out_bdput;
>  		memcpy(pinfo, info, sizeof(*info));
>  		p->info = pinfo;
>  	}
> @@ -470,6 +472,7 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  	}
>  
>  	/* everything is up and running, commence */
> +	bdev_add(bdev, devt);
>  	rcu_assign_pointer(ptbl->part[partno], p);
>  
>  	/* suppress uevent if the disk suppresses it */
> @@ -479,6 +482,8 @@ static struct hd_struct *add_partition(struct gendisk *disk, int partno,
>  
>  out_free_info:
>  	kfree(p->info);
> +out_bdput:
> +	bdput(bdev);
>  out_free_stats:
>  	free_percpu(p->dkstats);
>  out_free:
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 6d6e4d50834cd0..b350ed3af83bad 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -863,31 +863,46 @@ void __init bdev_cache_init(void)
>  	blockdev_superblock = bd_mnt->mnt_sb;   /* For writeback */
>  }
>  
> -static struct block_device *bdget(dev_t dev)
> +struct block_device *bdev_alloc(struct gendisk *disk, u8 partno)
>  {
>  	struct block_device *bdev;
>  	struct inode *inode;
>  
> -	inode = iget_locked(blockdev_superblock, dev);
> +	inode = new_inode(blockdev_superblock);
>  	if (!inode)
>  		return NULL;
> +	inode->i_mode = S_IFBLK;
> +	inode->i_rdev = 0;
> +	inode->i_data.a_ops = &def_blk_aops;
> +	mapping_set_gfp_mask(&inode->i_data, GFP_USER);
> +
> +	bdev = I_BDEV(inode);
> +	spin_lock_init(&bdev->bd_size_lock);
> +	bdev->bd_disk = disk;
> +	bdev->bd_partno = partno;
> +	bdev->bd_contains = NULL;
> +	bdev->bd_super = NULL;
> +	bdev->bd_inode = inode;
> +	bdev->bd_part_count = 0;
> +	return bdev;
> +}
>  
> -	bdev = &BDEV_I(inode)->bdev;
> +void bdev_add(struct block_device *bdev, dev_t dev)
> +{
> +	bdev->bd_dev = dev;
> +	bdev->bd_inode->i_rdev = dev;
> +	bdev->bd_inode->i_ino = dev;
> +	insert_inode_hash(bdev->bd_inode);
> +}
>  
> -	if (inode->i_state & I_NEW) {
> -		spin_lock_init(&bdev->bd_size_lock);
> -		bdev->bd_contains = NULL;
> -		bdev->bd_super = NULL;
> -		bdev->bd_inode = inode;
> -		bdev->bd_part_count = 0;
> -		bdev->bd_dev = dev;
> -		inode->i_mode = S_IFBLK;
> -		inode->i_rdev = dev;
> -		inode->i_data.a_ops = &def_blk_aops;
> -		mapping_set_gfp_mask(&inode->i_data, GFP_USER);
> -		unlock_new_inode(inode);
> -	}
> -	return bdev;
> +static struct block_device *bdget(dev_t dev)
> +{
> +	struct inode *inode;
> +
> +	inode = ilookup(blockdev_superblock, dev);
> +	if (!inode)
> +		return NULL;
> +	return &BDEV_I(inode)->bdev;
>  }
>  
>  /**
> @@ -1004,27 +1019,6 @@ int bd_prepare_to_claim(struct block_device *bdev, struct block_device *whole,
>  }
>  EXPORT_SYMBOL_GPL(bd_prepare_to_claim); /* only for the loop driver */
>  
> -static struct gendisk *bdev_get_gendisk(struct block_device *bdev, int *partno)
> -{
> -	struct gendisk *disk = get_gendisk(bdev->bd_dev, partno);
> -
> -	if (!disk)
> -		return NULL;
> -	/*
> -	 * Now that we hold gendisk reference we make sure bdev we looked up is
> -	 * not stale. If it is, it means device got removed and created before
> -	 * we looked up gendisk and we fail open in such case. Associating
> -	 * unhashed bdev with newly created gendisk could lead to two bdevs
> -	 * (and thus two independent caches) being associated with one device
> -	 * which is bad.
> -	 */
> -	if (inode_unhashed(bdev->bd_inode)) {
> -		put_disk_and_module(disk);
> -		return NULL;
> -	}
> -	return disk;
> -}
> -
>  static void bd_clear_claiming(struct block_device *whole, void *holder)
>  {
>  	lockdep_assert_held(&bdev_lock);
> @@ -1347,19 +1341,17 @@ EXPORT_SYMBOL_GPL(bdev_disk_changed);
>   *  mutex_lock(part->bd_mutex)
>   *    mutex_lock_nested(whole->bd_mutex, 1)
>   */
> -static int __blkdev_get(struct block_device *bdev, struct gendisk *disk,
> -		int partno, fmode_t mode)
> +static int __blkdev_get(struct block_device *bdev, fmode_t mode)
>  {
> +	struct gendisk *disk = bdev->bd_disk;
>  	int ret;
>  
>  	if (!bdev->bd_openers) {
> -		bdev->bd_disk = disk;
>  		bdev->bd_contains = bdev;
> -		bdev->bd_partno = partno;
>  
> -		if (!partno) {
> +		if (!bdev->bd_partno) {
>  			ret = -ENXIO;
> -			bdev->bd_part = disk_get_part(disk, partno);
> +			bdev->bd_part = disk_get_part(disk, 0);
>  			if (!bdev->bd_part)
>  				goto out_clear;
>  
> @@ -1388,7 +1380,7 @@ static int __blkdev_get(struct block_device *bdev, struct gendisk *disk,
>  			struct block_device *whole = bdget_disk(disk, 0);
>  
>  			mutex_lock_nested(&whole->bd_mutex, 1);
> -			ret = __blkdev_get(whole, disk, 0, mode);
> +			ret = __blkdev_get(whole, mode);
>  			if (ret) {
>  				mutex_unlock(&whole->bd_mutex);
>  				bdput(whole);
> @@ -1398,7 +1390,7 @@ static int __blkdev_get(struct block_device *bdev, struct gendisk *disk,
>  			mutex_unlock(&whole->bd_mutex);
>  
>  			bdev->bd_contains = whole;
> -			bdev->bd_part = disk_get_part(disk, partno);
> +			bdev->bd_part = disk_get_part(disk, bdev->bd_partno);
>  			if (!(disk->flags & GENHD_FL_UP) ||
>  			    !bdev->bd_part || !bdev->bd_part->nr_sects) {
>  				__blkdev_put(whole, mode, 1);
> @@ -1430,12 +1422,53 @@ static int __blkdev_get(struct block_device *bdev, struct gendisk *disk,
>  
>   out_clear:
>  	disk_put_part(bdev->bd_part);
> -	bdev->bd_disk = NULL;
>  	bdev->bd_part = NULL;
>  	bdev->bd_contains = NULL;
>  	return ret;
>  }
>  
> +struct block_device *blkdev_get_no_open(dev_t dev)
> +{
> +	struct block_device *bdev;
> +	struct gendisk *disk;
> +
> +	down_read(&bdev_lookup_sem);
> +	bdev = bdget(dev);
> +	if (!bdev) {
> +		up_read(&bdev_lookup_sem);
> +		blk_request_module(dev);
> +		down_read(&bdev_lookup_sem);
> +
> +		bdev = bdget(dev);
> +		if (!bdev)
> +			goto unlock;
> +	}
> +
> +	disk = bdev->bd_disk;
> +	if (!kobject_get_unless_zero(&disk_to_dev(disk)->kobj))
> +		goto bdput;
> +	if ((disk->flags & (GENHD_FL_UP | GENHD_FL_HIDDEN)) != GENHD_FL_UP)
> +		goto put_disk;
> +	if (!try_module_get(bdev->bd_disk->fops->owner))
> +		goto put_disk;
> +	up_read(&bdev_lookup_sem);
> +	return bdev;
> +put_disk:
> +	put_disk(disk);
> +bdput:
> +	bdput(bdev);
> +unlock:
> +	up_read(&bdev_lookup_sem);
> +	return NULL;
> +}
> +
> +void blkdev_put_no_open(struct block_device *bdev)
> +{
> +	module_put(bdev->bd_disk->fops->owner);
> +	put_disk(bdev->bd_disk);
> +	bdput(bdev);
> +}
> +
>  /**
>   * blkdev_get_by_dev - open a block device by device number
>   * @dev: device number of block device to open
> @@ -1463,7 +1496,6 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
>  	bool unblock_events = true;
>  	struct block_device *bdev;
>  	struct gendisk *disk;
> -	int partno;
>  	int ret;
>  
>  	ret = devcgroup_check_permission(DEVCG_DEV_BLOCK,
> @@ -1473,18 +1505,14 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
>  	if (ret)
>  		return ERR_PTR(ret);
>  
> -	bdev = bdget(dev);
> -	if (!bdev)
> -		return ERR_PTR(-ENOMEM);
> -
>  	/*
>  	 * If we lost a race with 'disk' being deleted, try again.  See md.c.
>  	 */
>  retry:
> -	ret = -ENXIO;
> -	disk = bdev_get_gendisk(bdev, &partno);
> -	if (!disk)
> -		goto bdput;
> +	bdev = blkdev_get_no_open(dev);
> +	if (!bdev)
> +		return ERR_PTR(-ENXIO);
> +	disk = bdev->bd_disk;
>  
>  	if (mode & FMODE_EXCL) {
>  		WARN_ON_ONCE(!holder);
> @@ -1492,7 +1520,7 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
>  		ret = -ENOMEM;
>  		claiming = bdget_disk(disk, 0);
>  		if (!claiming)
> -			goto put_disk;
> +			goto put_blkdev;
>  		ret = bd_prepare_to_claim(bdev, claiming, holder);
>  		if (ret)
>  			goto put_claiming;
> @@ -1501,12 +1529,10 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
>  	disk_block_events(disk);
>  
>  	mutex_lock(&bdev->bd_mutex);
> -	ret =__blkdev_get(bdev, disk, partno, mode);
> -	if (!(mode & FMODE_EXCL)) {
> -		; /* nothing to do here */
> -	} else if (ret) {
> -		bd_abort_claiming(bdev, claiming, holder);
> -	} else {
> +	ret =__blkdev_get(bdev, mode);
> +	if (ret)
> +		goto abort_claiming;
> +	if (mode & FMODE_EXCL) {
>  		bd_finish_claiming(bdev, claiming, holder);
>  
>  		/*
> @@ -1526,21 +1552,23 @@ struct block_device *blkdev_get_by_dev(dev_t dev, fmode_t mode, void *holder)
>  
>  	if (unblock_events)
>  		disk_unblock_events(disk);
> +	if (mode & FMODE_EXCL)
> +		bdput(claiming);
> +	return bdev;
>  
> +abort_claiming:
> +	if (mode & FMODE_EXCL)
> +		bd_abort_claiming(bdev, claiming, holder);
> +	mutex_unlock(&bdev->bd_mutex);
> +	disk_unblock_events(disk);
>  put_claiming:
>  	if (mode & FMODE_EXCL)
>  		bdput(claiming);
> -put_disk:
> -	if (ret)
> -		put_disk_and_module(disk);
> +put_blkdev:
> +	blkdev_put_no_open(bdev);
>  	if (ret == -ERESTARTSYS)
>  		goto retry;
> -bdput:
> -	if (ret) {
> -		bdput(bdev);
> -		return ERR_PTR(ret);
> -	}
> -	return bdev;
> +	return ERR_PTR(ret);
>  }
>  EXPORT_SYMBOL(blkdev_get_by_dev);
>  
> @@ -1641,7 +1669,6 @@ static void __blkdev_put(struct block_device *bdev, fmode_t mode, int for_part)
>  
>  		disk_put_part(bdev->bd_part);
>  		bdev->bd_part = NULL;
> -		bdev->bd_disk = NULL;
>  		if (bdev_is_partition(bdev))
>  			victim = bdev->bd_contains;
>  		bdev->bd_contains = NULL;
> @@ -1699,12 +1726,10 @@ void blkdev_put(struct block_device *bdev, fmode_t mode)
>  	 * from userland - e.g. eject(1).
>  	 */
>  	disk_flush_events(disk, DISK_EVENT_MEDIA_CHANGE);
> -
>  	mutex_unlock(&bdev->bd_mutex);
>  
>  	__blkdev_put(bdev, mode, 0);
> -	bdput(bdev);
> -	put_disk_and_module(disk);
> +	blkdev_put_no_open(bdev);
>  }
>  EXPORT_SYMBOL(blkdev_put);
>  
> diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h
> index c8fc9792ac776d..b9f3c246c3c908 100644
> --- a/include/linux/blk-cgroup.h
> +++ b/include/linux/blk-cgroup.h
> @@ -197,12 +197,12 @@ void blkcg_print_blkgs(struct seq_file *sf, struct blkcg *blkcg,
>  u64 __blkg_prfill_u64(struct seq_file *sf, struct blkg_policy_data *pd, u64 v);
>  
>  struct blkg_conf_ctx {
> -	struct gendisk			*disk;
> +	struct block_device		*bdev;
>  	struct blkcg_gq			*blkg;
>  	char				*body;
>  };
>  
> -struct gendisk *blkcg_conf_get_disk(char **inputp);
> +struct block_device *blkcg_conf_open_bdev(char **inputp);
>  int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol,
>  		   char *input, struct blkg_conf_ctx *ctx);
>  void blkg_conf_finish(struct blkg_conf_ctx *ctx);
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index bdd7339bcda462..5d48b92f5e4348 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1994,6 +1994,12 @@ void bd_abort_claiming(struct block_device *bdev, struct block_device *whole,
>  		void *holder);
>  void blkdev_put(struct block_device *bdev, fmode_t mode);
>  
> +/* just for blk-cgroup, don't use elsewhere */
> +struct block_device *blkdev_get_no_open(dev_t dev);
> +void blkdev_put_no_open(struct block_device *bdev);
> +
> +struct block_device *bdev_alloc(struct gendisk *disk, u8 partno);
> +void bdev_add(struct block_device *bdev, dev_t dev);
>  struct block_device *I_BDEV(struct inode *inode);
>  struct block_device *bdget_part(struct hd_struct *part);
>  struct block_device *bdgrab(struct block_device *bdev);
> diff --git a/include/linux/genhd.h b/include/linux/genhd.h
> index ca5e356084c353..42a51653c7303e 100644
> --- a/include/linux/genhd.h
> +++ b/include/linux/genhd.h
> @@ -65,6 +65,7 @@ struct hd_struct {
>  	struct disk_stats __percpu *dkstats;
>  	struct percpu_ref ref;
>  
> +	struct block_device *bdev;
>  	struct device __dev;
>  	struct kobject *holder_dir;
>  	int policy, partno;
> @@ -193,7 +194,6 @@ struct gendisk {
>  	int flags;
>  	unsigned long state;
>  #define GD_NEED_PART_SCAN		0
> -	struct rw_semaphore lookup_sem;
>  	struct kobject *slave_dir;
>  
>  	struct timer_rand_state *random;
> @@ -300,7 +300,6 @@ static inline void add_disk_no_queue_reg(struct gendisk *disk)
>  }
>  
>  extern void del_gendisk(struct gendisk *gp);
> -extern struct gendisk *get_gendisk(dev_t dev, int *partno);
>  extern struct block_device *bdget_disk(struct gendisk *disk, int partno);
>  
>  extern void set_disk_ro(struct gendisk *disk, int flag);
> @@ -338,7 +337,6 @@ int blk_drop_partitions(struct block_device *bdev);
>  
>  extern struct gendisk *__alloc_disk_node(int minors, int node_id);
>  extern void put_disk(struct gendisk *disk);
> -extern void put_disk_and_module(struct gendisk *disk);
>  
>  #define alloc_disk_node(minors, node_id)				\
>  ({									\
> @@ -388,7 +386,10 @@ static inline void bd_unlink_disk_holder(struct block_device *bdev,
>  }
>  #endif /* CONFIG_SYSFS */
>  
> +extern struct rw_semaphore bdev_lookup_sem;
> +
>  dev_t blk_lookup_devt(const char *name, int partno);
> +void blk_request_module(dev_t devt);
>  #ifdef CONFIG_BLOCK
>  void printk_all_partitions(void);
>  #else /* CONFIG_BLOCK */
> -- 
> 2.29.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR