Re: [PATCH] block: Discard page cache of zone reset target range

[Kanchan Joshi <joshiiitr@gmail.com>]

On Mon, Mar 8, 2021 at 2:11 PM Shin'ichiro Kawasaki
<shinichiro.kawasaki@wdc.com> wrote:
>
> When zone reset ioctl and data read race for a same zone on zoned block
> devices, the data read leaves stale page cache even though the zone
> reset ioctl zero clears all the zone data on the device. To avoid
> non-zero data read from the stale page cache after zone reset, discard
> page cache of reset target zones. In same manner as fallocate, call the
> function truncate_bdev_range() in blkdev_zone_mgmt_ioctl() before and
> after zone reset to ensure the page cache discarded.
>
> This patch can be applied back to the stable kernel version v5.10.y.
> Rework is needed for older stable kernels.
>
> Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
> Fixes: 3ed05a987e0f ("blk-zoned: implement ioctls")
> Cc: <stable@vger.kernel.org> # 5.10+
> ---
>  block/blk-zoned.c | 30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/block/blk-zoned.c b/block/blk-zoned.c
> index 833978c02e60..990a36be2927 100644
> --- a/block/blk-zoned.c
> +++ b/block/blk-zoned.c
> @@ -329,6 +329,9 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, fmode_t mode,
>         struct request_queue *q;
>         struct blk_zone_range zrange;
>         enum req_opf op;
> +       sector_t capacity;
> +       loff_t start, end;
> +       int ret;
>
>         if (!argp)
>                 return -EINVAL;
> @@ -349,9 +352,22 @@ int blkdev_zone_mgmt_ioctl(struct block_device *bdev, fmode_t mode,
>         if (copy_from_user(&zrange, argp, sizeof(struct blk_zone_range)))
>                 return -EFAULT;
>
> +       capacity = get_capacity(bdev->bd_disk);
> +       if (zrange.sector + zrange.nr_sectors <= zrange.sector ||
> +           zrange.sector + zrange.nr_sectors > capacity)
> +               /* Out of range */
> +               return -EINVAL;
> +
> +       start = zrange.sector << SECTOR_SHIFT;
> +       end = ((zrange.sector + zrange.nr_sectors) << SECTOR_SHIFT) - 1;

How about doing all this calculation only when it is applicable i.e.
only for reset-zone case, and not for other cases (open/close/finish
zone).

Also apart from "out of range" (which is covered here), there are few
more cases when blkdev_zone_mgmt() may fail it (not covered here).
Perhaps the whole pre and post truncate part can fit better inside
blkdev_zone_mgmt itself.

-- 
Kanchan