On Wed, May 12, 2021 at 06:50:49PM +0200, Christoph Hellwig wrote:
> As an aritfact of how gendisk lookup used to work in earlier kernels,
> GENHD_FL_UP is only cleared very late in del_gendisk, and instead a
> global lock is used to prevent opens from actually succeeding. Clear
> the flag, and remove the bdev inode from the inode hash earlier to
> ensure lookups fail from the very beginning of del_gendisk, and remove
> the now not needed bdev_lookup_sem.
>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
> block/genhd.c | 19 ++-----------------
> fs/block_dev.c | 9 +--------
> include/linux/genhd.h | 2 --
> 3 files changed, 3 insertions(+), 27 deletions(-)
>
> diff --git a/block/genhd.c b/block/genhd.c
> index 39ca97b0edc6..1693e520ec7d 100644
> --- a/block/genhd.c
> +++ b/block/genhd.c
> @@ -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);
> @@ -609,28 +607,15 @@ 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;
> + remove_inode_hash(disk->part0->bd_inode);
> blk_drop_partitions(disk);
> mutex_unlock(&disk->part0->bd_mutex);
Both bdget() and checking FL_UP is done without holding ->bd_mutex, so
del_gendisk() may be run after checking FL_UP is completed in blkdev_get_no_open(),
then new opener is still allowed even after the bdev is invalidated.
Given this patch is for 5.13, I'd suggest to not move remove_inode_hash()
inside the lock block, which isn't necessary, and it is enough to move
clearing FL_UP with the following change together:
diff --git a/fs/block_dev.c b/fs/block_dev.c
index b8abccd03e5d..31a6d54edf6d 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -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;
Thanks,
Ming
