[PATCH] block: Fix BLKRRPART regression

[Saranya Muruganandam <saranyamohan@google.com>]

The BLKRRPART ioctl used to report errors such as EIO before we changed
the blkdev_reread_part() logic.

Lets add a flag and capture the errors returned by bdev_disk_changed()
when the flag is set. Setting this flag for the BLKRRPART path when we
want the errors to be reported when rereading partitions on the disk.

Link: https://lore.kernel.org/all/20240320015134.GA14267@lst.de/
Suggested-by: Christoph Hellwig <hch@lst.de>
Tested: Tested by simulating failure to the block device and will
propose a new test to blktests.
Fixes: 4601b4b130de ("block: reopen the device in blkdev_reread_part")
Reported-by: Saranya Muruganandam <saranyamohan@google.com>
Signed-off-by: Saranya Muruganandam <saranyamohan@google.com>

Change-Id: Idf3d97390ed78061556f8468d10d6cab24ae20b1
---
 block/bdev.c           | 31 +++++++++++++++++++++----------
 block/ioctl.c          |  3 ++-
 include/linux/blkdev.h |  3 +++
 3 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index 77fa77cd29bee..71478f8865546 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -632,6 +632,14 @@ static void blkdev_flush_mapping(struct block_device *bdev)
 	bdev_write_inode(bdev);
 }
 
+static void blkdev_put_whole(struct block_device *bdev)
+{
+	if (atomic_dec_and_test(&bdev->bd_openers))
+		blkdev_flush_mapping(bdev);
+	if (bdev->bd_disk->fops->release)
+		bdev->bd_disk->fops->release(bdev->bd_disk);
+}
+
 static int blkdev_get_whole(struct block_device *bdev, blk_mode_t mode)
 {
 	struct gendisk *disk = bdev->bd_disk;
@@ -650,18 +658,21 @@ static int blkdev_get_whole(struct block_device *bdev, blk_mode_t mode)
 
 	if (!atomic_read(&bdev->bd_openers))
 		set_init_blocksize(bdev);
-	if (test_bit(GD_NEED_PART_SCAN, &disk->state))
-		bdev_disk_changed(disk, false);
 	atomic_inc(&bdev->bd_openers);
-	return 0;
-}
 
-static void blkdev_put_whole(struct block_device *bdev)
-{
-	if (atomic_dec_and_test(&bdev->bd_openers))
-		blkdev_flush_mapping(bdev);
-	if (bdev->bd_disk->fops->release)
-		bdev->bd_disk->fops->release(bdev->bd_disk);
+	if (test_bit(GD_NEED_PART_SCAN, &disk->state)) {
+		/*
+		 * Only return scanning errors if we are called from contexts
+		 * that explicitly want them, e.g. the BLKRRPART ioctl.
+		 */
+		ret = bdev_disk_changed(disk, false);
+		if (ret && (mode & BLK_OPEN_STRICT_SCAN)) {
+			blkdev_put_whole(bdev);
+			return ret;
+		}
+	}
+
+	return 0;
 }
 
 static int blkdev_get_part(struct block_device *part, blk_mode_t mode)
diff --git a/block/ioctl.c b/block/ioctl.c
index aa46f3761c3ed..e8d72d9f327fd 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -557,7 +557,8 @@ static int blkdev_common_ioctl(struct block_device *bdev, blk_mode_t mode,
 			return -EACCES;
 		if (bdev_is_partition(bdev))
 			return -EINVAL;
-		return disk_scan_partitions(bdev->bd_disk, mode);
+		return disk_scan_partitions(bdev->bd_disk,
+				mode | BLK_OPEN_STRICT_SCAN);
 	case BLKTRACESTART:
 	case BLKTRACESTOP:
 	case BLKTRACETEARDOWN:
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 01983eece8f2a..d0104dc839b0d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -151,6 +151,9 @@ struct access_rules_head {
 	int max_rules;
 };
 
+/* return partition scanning errors */
+#define BLK_OPEN_STRICT_SCAN	((__force blk_mode_t)(1 << 5))
+
 struct gendisk {
 	/*
 	 * major/first_minor/minors should not be set by any new driver, the
-- 
2.44.0.478.gd926399ef9-goog