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: Christoph Hellwig <hch@lst.de>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20210514131842.1600568-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/genhd.c b/block/genhd.c
index 39ca97b0edc612ad2828952e7424d0a232bbf640..9f8cb7beaad1160b249912919e6fcf4e1f9c1a11 100644 (file)
--- 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);
@@ -609,13 +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");

diff --git a/fs/block_dev.c b/fs/block_dev.c
index eb265d72fce89b43266ffec40fb6b9ffa38a1689..580bae995b87980010e9ad716a7ade4c4fe22b4c 100644 (file)
--- 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;
@@ -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;
 }
 

diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 7e9660ea967d59c422d5ed6a9b6d557a66f86e04..6fc26f7bdf71ea48a7ca1693217f8be150d2d5d7 100644 (file)
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -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