Re: [PATCH] block: Fix BLKRRPART regression

Shinichiro Kawasaki
2024-04-10T05:04:18Z

Saranya, while I evaluate the corresponding patch for blktests, I found a
weird behavior, and had a chance to look into this patch. Please find my
comments in line.

On Apr 06, 2024 / 04:46, Saranya Muruganandam wrote:
> 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.

Documentation/process/submitting-patches.rst guides to describe changes in
imperative mood, then the sentences above can be rephrased like,

Add a flag...
Set this flag...

>
> 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..42940bced33bb 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 conexts

s/conexts/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..3ed5e03109c29 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 << 5))

The line above assigns the same number for BLK_OPEN_STRICT_SCAN and
BLK_OPEN_RESTRICT_WRITES, then blockdev --rereadpt fails with EINVAL,
not EIO. I modified it to "1 << 6", then it looks working good.

>
> struct gendisk {
> /*
> --
> 2.44.0.478.gd926399ef9-goog
>