Re: [PATCH v2] block: Try to handle busy underlying device on discard

[Jan Kara <jack@suse.cz>]

On Mon 22-02-21 10:48:09, Jan Kara wrote:
> Commit 384d87ef2c95 ("block: Do not discard buffers under a mounted
> filesystem") made paths issuing discard or zeroout requests to the
> underlying device try to grab block device in exclusive mode. If that
> failed we returned EBUSY to userspace. This however caused unexpected
> fallout in userspace where e.g. FUSE filesystems issue discard requests
> from userspace daemons although the device is open exclusively by the
> kernel. Also shrinking of logical volume by LVM issues discard requests
> to a device which may be claimed exclusively because there's another LV
> on the same PV. So to avoid these userspace regressions, fall back to
> invalidate_inode_pages2_range() instead of returning EBUSY to userspace
> and return EBUSY only of that call fails as well (meaning that there's
> indeed someone using the particular device range we are trying to
> discard).
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=211167
> Fixes: 384d87ef2c95 ("block: Do not discard buffers under a mounted filesystem")
> CC: stable@vger.kernel.org
> Signed-off-by: Jan Kara <jack@suse.cz>

Before I forget: I'd like to add two tested by tags to give credit to
people who helped with testing.

Tested-by: Richard W.M. Jones <rjones@redhat.com>
Tested-by: Andreas Klauer <Andreas.Klauer@metamorpher.de>

									Honza

> ---
>  fs/block_dev.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/block_dev.c b/fs/block_dev.c
> index 235b5042672e..c33151020bcd 100644
> --- a/fs/block_dev.c
> +++ b/fs/block_dev.c
> @@ -118,13 +118,22 @@ int truncate_bdev_range(struct block_device *bdev, fmode_t mode,
>  	if (!(mode & FMODE_EXCL)) {
>  		int err = bd_prepare_to_claim(bdev, truncate_bdev_range);
>  		if (err)
> -			return err;
> +			goto invalidate;
>  	}
>  
>  	truncate_inode_pages_range(bdev->bd_inode->i_mapping, lstart, lend);
>  	if (!(mode & FMODE_EXCL))
>  		bd_abort_claiming(bdev, truncate_bdev_range);
>  	return 0;
> +
> +invalidate:
> +	/*
> +	 * Someone else has handle exclusively open. Try invalidating instead.
> +	 * The 'end' argument is inclusive so the rounding is safe.
> +	 */
> +	return invalidate_inode_pages2_range(bdev->bd_inode->i_mapping,
> +					     lstart >> PAGE_SHIFT,
> +					     lend >> PAGE_SHIFT);
>  }
>  EXPORT_SYMBOL(truncate_bdev_range);
>  
> -- 
> 2.26.2
> 
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR