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

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2021/03/09 14:49, Kanchan Joshi wrote:
> 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.

No, I do not think so. That would add overhead for in-kernel users of zone reset
for no good reason since these would typically take care of cached pages
themselves (e.g. FS) and would not trigger page caching using the bdev inode anyway.



-- 
Damien Le Moal
Western Digital Research