[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.

Add a flag and capture the errors returned by bdev_disk_changed()
when the flag is set. Set 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           | 29 +++++++++++++++++++----------
 block/ioctl.c          |  3 ++-
 include/linux/blkdev.h |  2 ++
 3 files changed, 23 insertions(+), 11 deletions(-)

diff --git a/block/bdev.c b/block/bdev.c
index 7a5f611c3d2e3..cea51dca87531 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -652,6 +652,14 @@ 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;
@@ -670,20 +678,21 @@ 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);
+	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 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_part(struct block_device *part, blk_mode_t mode)
 {
 	struct gendisk *disk = part->bd_disk;
diff --git a/block/ioctl.c b/block/ioctl.c
index 0c76137adcaaa..128f503828cee 100644
--- a/block/ioctl.c
+++ b/block/ioctl.c
@@ -562,7 +562,8 @@ 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 c3e8f7cf96be9..d16320852c4ba 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -128,6 +128,8 @@ typedef unsigned int __bitwise blk_mode_t;
 #define BLK_OPEN_WRITE_IOCTL	((__force blk_mode_t)(1 << 4))
 /* open is exclusive wrt all other BLK_OPEN_WRITE opens to the device */
 #define BLK_OPEN_RESTRICT_WRITES	((__force blk_mode_t)(1 << 5))
+/* return partition scanning errors */
+#define BLK_OPEN_STRICT_SCAN	((__force blk_mode_t)(1 << 6))
 
 struct gendisk {
 	/*
-- 
2.44.0.683.g7961c838ac-goog