From 6c60ff048ca1e0739f39aa25996543c6e662a46c Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch@lst.de>
Date: Fri, 14 May 2021 15:18:41 +0200
Subject: [PATCH] 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>
---
block/genhd.c | 11 +----------
fs/block_dev.c | 15 +++++----------
include/linux/genhd.h | 2 --
3 files changed, 6 insertions(+), 22 deletions(-)
diff --git a/block/genhd.c b/block/genhd.c
index 39ca97b0edc61..9f8cb7beaad11 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);
@@ -609,13 +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 eb265d72fce89..580bae995b879 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;
@@ -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 7e9660ea967d5..6fc26f7bdf71e 100644
--- 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
--
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