[RFC PATCH V3 1/1] block: reject I/O for same fd if block size changed

[Minwoo Im <minwoo.im.dev@gmail.com>]

This patch fixes I/O errors during BLKRRPART ioctl() behavior right
after format operation that changed logical block size of the block
device with a same file descriptor opened.

This issue can be easily reproduced with a single format command in case
of NVMe (logical block size 512B to 4096B).

	nvme format /dev/nvme0n1 --lbaf=1 --force

This is because the application, nvme-cli format subcommand issues an
admin command followed by BLKRRPART ioctl to re-read partition
information without closing the file descriptor.  If file descriptor
stays opened, __blkdev_get() will not be invoked at all even logical
block size has been changed.

It will cause I/O errors with invalid Read operations during the
BLKRRPART ioctl due to i_blkbits mismatch. The invalid operations in
BLKRRPART happens with under-flowed Number of LBA(NLB) values
0xffff(65535) because i_blkbits is still set to 9 even the logical block
size has been updated to 4096.  The BLKRRPART will lead buffer_head to
hold 512B data which is less than the logical lock size of the block
device.

The root cause, which is because i_blkbits of inode of the block device
is not updated, can be solved easily by re-opening file descriptor
again from application.  But, that's just for application's business
and kernel should reject invalid Read operations during the BLKRRPART
ioctl.

This patch rejects I/O from the path of add_partitions() to avoid
issuing invalid Read operations to device.  It also sets a flag to
gendisk in blk_queue_logical_block_size to minimize caller-side updates.

Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
---
 block/blk-settings.c    |  8 ++++++++
 block/partitions/core.c | 11 +++++++++++
 fs/block_dev.c          |  6 ++++++
 include/linux/genhd.h   |  1 +
 4 files changed, 26 insertions(+)

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 43990b1d148b..84136ea4e2a4 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -328,6 +328,14 @@ EXPORT_SYMBOL(blk_queue_max_segment_size);
 void blk_queue_logical_block_size(struct request_queue *q, unsigned int size)
 {
 	struct queue_limits *limits = &q->limits;
+	struct block_device *bdev;
+
+	if (q->backing_dev_info && q->backing_dev_info->owner &&
+			limits->logical_block_size != size) {
+		bdev = blkdev_get_no_open(q->backing_dev_info->owner->devt);
+		bdev->bd_disk->flags |= GENHD_FL_BLOCK_SIZE_CHANGED;
+		blkdev_put_no_open(bdev);
+	}
 
 	limits->logical_block_size = size;
 
diff --git a/block/partitions/core.c b/block/partitions/core.c
index e7d776db803b..5a0330c1b6f9 100644
--- a/block/partitions/core.c
+++ b/block/partitions/core.c
@@ -618,6 +618,17 @@ int blk_add_partitions(struct gendisk *disk, struct block_device *bdev)
 	if (!disk_part_scan_enabled(disk))
 		return 0;
 
+	/*
+	 * Reject to check partition information if block size has been changed
+	 * in the runtime.  If block size of a block device has been changed,
+	 * the file descriptor should be opened agian to update the blkbits.
+	 */
+	if (disk->flags & GENHD_FL_BLOCK_SIZE_CHANGED) {
+		pr_warn("%s: rejecting checking partition. fd should be opened again.\n",
+				disk->disk_name);
+		return -EBADFD;
+	}
+
 	state = check_partition(disk, bdev);
 	if (!state)
 		return 0;
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 9293045e128c..c996de3d6084 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -131,6 +131,12 @@ EXPORT_SYMBOL(truncate_bdev_range);
 static void set_init_blocksize(struct block_device *bdev)
 {
 	bdev->bd_inode->i_blkbits = blksize_bits(bdev_logical_block_size(bdev));
+
+	/*
+	 * Allow I/O commands for this block device.  We can say that this
+	 * block device has been set to a proper block size.
+	 */
+	bdev->bd_disk->flags &= ~GENHD_FL_BLOCK_SIZE_CHANGED;
 }
 
 int set_blocksize(struct block_device *bdev, int size)
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 809aaa32d53c..0e0e24917003 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -103,6 +103,7 @@ struct partition_meta_info {
 #define GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE	0x0100
 #define GENHD_FL_NO_PART_SCAN			0x0200
 #define GENHD_FL_HIDDEN				0x0400
+#define GENHD_FL_BLOCK_SIZE_CHANGED		0x0800
 
 enum {
 	DISK_EVENT_MEDIA_CHANGE			= 1 << 0, /* media changed */
-- 
2.17.1