block: split __blkdev_get

Split __blkdev_get into one helper for the whole device, and one for
opening partitions.  This removes the (bounded) recursion when opening
a partition.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20210525061301.2242282-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 6cc4d4c..2b5073e 100644 (file)
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1290,78 +1290,68 @@ rescan:
  */
 EXPORT_SYMBOL_GPL(bdev_disk_changed);
 
-/*
- * bd_mutex locking:
- *
- *  mutex_lock(part->bd_mutex)
- *    mutex_lock_nested(whole->bd_mutex, 1)
- */
-static int __blkdev_get(struct block_device *bdev, fmode_t mode)
+static int blkdev_get_whole(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 (disk->fops->open) {
+               ret = disk->fops->open(bdev, mode);
+               if (ret) {
+                       /* avoid ghost partitions on a removed medium */
+                       if (ret == -ENOMEDIUM &&
+                            test_bit(GD_NEED_PART_SCAN, &disk->state))
+                               bdev_disk_changed(bdev, true);
+                       return ret;
+               }
+       }
 
        if (!bdev->bd_openers) {
-               if (!bdev_is_partition(bdev)) {
-                       ret = 0;
-                       if (disk->fops->open)
-                               ret = disk->fops->open(bdev, mode);
+               set_init_blocksize(bdev);
+               if (bdev->bd_bdi == &noop_backing_dev_info)
+                       bdev->bd_bdi = bdi_get(disk->queue->backing_dev_info);
+       }
+       if (test_bit(GD_NEED_PART_SCAN, &disk->state))
+               bdev_disk_changed(bdev, false);
+       bdev->bd_openers++;
+       return 0;;
+}
 
-                       if (!ret)
-                               set_init_blocksize(bdev);
+static int blkdev_get_part(struct block_device *part, fmode_t mode)
+{
+       struct gendisk *disk = part->bd_disk;
+       struct block_device *whole;
+       int ret;
 
-                       /*
-                        * If the device is invalidated, rescan partition
-                        * if open succeeded or failed with -ENOMEDIUM.
-                        * The latter is necessary to prevent ghost
-                        * partitions on a removed medium.
-                        */
-                       if (test_bit(GD_NEED_PART_SCAN, &disk->state) &&
-                           (!ret || ret == -ENOMEDIUM))
-                               bdev_disk_changed(bdev, ret == -ENOMEDIUM);
+       if (part->bd_openers)
+               goto done;
 
-                       if (ret)
-                               return ret;
-               } else {
-                       struct block_device *whole = bdgrab(disk->part0);
-
-                       mutex_lock_nested(&whole->bd_mutex, 1);
-                       ret = __blkdev_get(whole, mode);
-                       if (ret) {
-                               mutex_unlock(&whole->bd_mutex);
-                               bdput(whole);
-                               return ret;
-                       }
-                       whole->bd_part_count++;
-                       mutex_unlock(&whole->bd_mutex);
+       whole = bdgrab(disk->part0);
+       mutex_lock_nested(&whole->bd_mutex, 1);
+       ret = blkdev_get_whole(whole, mode);
+       if (ret) {
+               mutex_unlock(&whole->bd_mutex);
+               goto out_put_whole;
+       }
+       whole->bd_part_count++;
+       mutex_unlock(&whole->bd_mutex);
 
-                       if (!bdev_nr_sectors(bdev)) {
-                               __blkdev_put(whole, mode, 1);
-                               bdput(whole);
-                               return -ENXIO;
-                       }
-                       set_init_blocksize(bdev);
-               }
+       ret = -ENXIO;
+       if (!bdev_nr_sectors(part))
+               goto out_blkdev_put;
 
-               if (bdev->bd_bdi == &noop_backing_dev_info)
-                       bdev->bd_bdi = bdi_get(disk->queue->backing_dev_info);
-       } else {
-               if (!bdev_is_partition(bdev)) {
-                       if (bdev->bd_disk->fops->open)
-                               ret = bdev->bd_disk->fops->open(bdev, mode);
-                       /* the same as first opener case, read comment there */
-                       if (test_bit(GD_NEED_PART_SCAN, &disk->state) &&
-                           (!ret || ret == -ENOMEDIUM))
-                               bdev_disk_changed(bdev, ret == -ENOMEDIUM);
-                       if (ret)
-                               return ret;
-               }
-       }
-       bdev->bd_openers++;
+       set_init_blocksize(part);
+       if (part->bd_bdi == &noop_backing_dev_info)
+               part->bd_bdi = bdi_get(disk->queue->backing_dev_info);
+done:
+       part->bd_openers++;
        return 0;
+
+out_blkdev_put:
+       __blkdev_put(whole, mode, 1);
+out_put_whole:
+       bdput(whole);
+       return ret;
 }
 
 struct block_device *blkdev_get_no_open(dev_t dev)
@@ -1448,7 +1438,13 @@ 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, mode);
+       ret = -ENXIO;
+       if (!(disk->flags & GENHD_FL_UP))
+               goto abort_claiming;
+       if (bdev_is_partition(bdev))
+               ret = blkdev_get_part(bdev, mode);
+       else
+               ret = blkdev_get_whole(bdev, mode);
        if (ret)
                goto abort_claiming;
        if (mode & FMODE_EXCL) {