On Mon, Aug 28, 2023 at 10:04 AM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
>
> From: Yu Kuai <yukuai3@xxxxxxxxxx>
>
> Because reading 'suspend_lo' and 'suspend_hi' from md_handle_request()
> is not protected, use READ_ONCE/WRITE_ONCE to prevent reading abnormal
> value.
Hi Kuai
If we don't use READ_ONCE/WRITE_ONCE, What's the risk here? Could you
explain in detail or give an example?
Regards
Xiao
>
> Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> ---
> drivers/md/md.c | 16 +++++++++-------
> 1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 46badd13a687..9d8dff9d923c 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -359,11 +359,11 @@ static bool is_suspended(struct mddev *mddev, struct bio *bio)
> return true;
> if (bio_data_dir(bio) != WRITE)
> return false;
> - if (mddev->suspend_lo >= mddev->suspend_hi)
> + if (READ_ONCE(mddev->suspend_lo) >= READ_ONCE(mddev->suspend_hi))
> return false;
> - if (bio->bi_iter.bi_sector >= mddev->suspend_hi)
> + if (bio->bi_iter.bi_sector >= READ_ONCE(mddev->suspend_hi))
> return false;
> - if (bio_end_sector(bio) < mddev->suspend_lo)
> + if (bio_end_sector(bio) < READ_ONCE(mddev->suspend_lo))
> return false;
> return true;
> }
> @@ -5171,7 +5171,8 @@ __ATTR(sync_max, S_IRUGO|S_IWUSR, max_sync_show, max_sync_store);
> static ssize_t
> suspend_lo_show(struct mddev *mddev, char *page)
> {
> - return sprintf(page, "%llu\n", (unsigned long long)mddev->suspend_lo);
> + return sprintf(page, "%llu\n",
> + (unsigned long long)READ_ONCE(mddev->suspend_lo));
> }
>
> static ssize_t
> @@ -5191,7 +5192,7 @@ suspend_lo_store(struct mddev *mddev, const char *buf, size_t len)
> return err;
>
> mddev_suspend(mddev);
> - mddev->suspend_lo = new;
> + WRITE_ONCE(mddev->suspend_lo, new);
> mddev_resume(mddev);
>
> mddev_unlock(mddev);
> @@ -5203,7 +5204,8 @@ __ATTR(suspend_lo, S_IRUGO|S_IWUSR, suspend_lo_show, suspend_lo_store);
> static ssize_t
> suspend_hi_show(struct mddev *mddev, char *page)
> {
> - return sprintf(page, "%llu\n", (unsigned long long)mddev->suspend_hi);
> + return sprintf(page, "%llu\n",
> + (unsigned long long)READ_ONCE(mddev->suspend_hi));
> }
>
> static ssize_t
> @@ -5223,7 +5225,7 @@ suspend_hi_store(struct mddev *mddev, const char *buf, size_t len)
> return err;
>
> mddev_suspend(mddev);
> - mddev->suspend_hi = new;
> + WRITE_ONCE(mddev->suspend_hi, new);
> mddev_resume(mddev);
>
> mddev_unlock(mddev);
> --
> 2.39.2
>
