Commit 6c60ff04 authored by Christoph Hellwig's avatar Christoph Hellwig Committed by Jens Axboe
Browse files

block: prevent block device lookups at the beginning of del_gendisk 



As an artifact of how gendisk lookup used to work in earlier kernels,
GENHD_FL_UP is only cleared very late in del_gendisk, and a global lock
is used to prevent opens from succeeding while del_gendisk is tearing
down the gendisk.  Switch to clearing the flag early and under bd_mutex
so that callers can use bd_mutex to stabilize the flag, which removes
the need for the global mutex.

Signed-off-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarMing Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210514131842.1600568-2-hch@lst.de


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent 9a66e6bd

block/genhd.c

+1 −10
Original line number Diff line number Diff line
@@ -29,8 +29,6 @@ 


static struct kobject *block_depr;



DECLARE_RWSEM(bdev_lookup_sem);



/* for extended dynamic devt allocation, currently only one major is used */

#define NR_EXT_DEVT		(1 << MINORBITS)

static DEFINE_IDA(ext_devt_ida);
@@ -609,13 +607,8 @@ void del_gendisk(struct gendisk *disk) 
	blk_integrity_del(disk);

	disk_del_events(disk);



	/*

	 * Block lookups of the disk until all bdevs are unhashed and the

	 * disk is marked as dead (GENHD_FL_UP cleared).

	 */

	down_write(&bdev_lookup_sem);



	mutex_lock(&disk->part0->bd_mutex);

	disk->flags &= ~GENHD_FL_UP;

	blk_drop_partitions(disk);

	mutex_unlock(&disk->part0->bd_mutex);
@@ -629,8 +622,6 @@ void del_gendisk(struct gendisk *disk) 
	remove_inode_hash(disk->part0->bd_inode);



	set_capacity(disk, 0);

	disk->flags &= ~GENHD_FL_UP;

	up_write(&bdev_lookup_sem);



	if (!(disk->flags & GENHD_FL_HIDDEN)) {

		sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");

fs/block_dev.c

+5 −10
Original line number Diff line number Diff line
@@ -1298,6 +1298,9 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode) 
	struct gendisk *disk = bdev->bd_disk;

	int ret = 0;



	if (!(disk->flags & GENHD_FL_UP))

		return -ENXIO;



	if (!bdev->bd_openers) {

		if (!bdev_is_partition(bdev)) {

			ret = 0;
@@ -1332,8 +1335,7 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode) 
			whole->bd_part_count++;

			mutex_unlock(&whole->bd_mutex);



			if (!(disk->flags & GENHD_FL_UP) ||

			    !bdev_nr_sectors(bdev)) {

			if (!bdev_nr_sectors(bdev)) {

				__blkdev_put(whole, mode, 1);

				bdput(whole);

				return -ENXIO;
@@ -1364,16 +1366,12 @@ 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;

			return NULL;

	}



	disk = bdev->bd_disk;
@@ -1383,14 +1381,11 @@ struct block_device *blkdev_get_no_open(dev_t dev) 
		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;

}

include/linux/genhd.h

+0 −2
Original line number Diff line number Diff line
@@ -306,8 +306,6 @@ 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