Re: [PATCH v2 1/5] md/md-llbitmap: skip reading rdevs that are not in_sync

[Xiao Ni]

On Mon, Feb 23, 2026 at 10:41 AM Yu Kuai <yukuai@xxxxxxxxx> wrote:
>
> When reading bitmap pages from member disks, the code iterates through
> all rdevs and attempts to read from the first available one. However,
> it only checks for raid_disk assignment and Faulty flag, missing the
> In_sync flag check.
>
> This can cause bitmap data to be read from spare disks that are still
> being rebuilt and don't have valid bitmap information yet. Reading
> stale or uninitialized bitmap data from such disks can lead to
> incorrect dirty bit tracking, potentially causing data corruption
> during recovery or normal operation.
>
> Add the In_sync flag check to ensure bitmap pages are only read from
> fully synchronized member disks that have valid bitmap data.
>
> Cc: stable@xxxxxxxxxxxxxxx
> Fixes: 5ab829f1971d ("md/md-llbitmap: introduce new lockless bitmap")
> Signed-off-by: Yu Kuai <yukuai@xxxxxxxxx>
> ---
>  drivers/md/md-llbitmap.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/md/md-llbitmap.c b/drivers/md/md-llbitmap.c
> index cd713a7dc270..30d7e36b22c4 100644
> --- a/drivers/md/md-llbitmap.c
> +++ b/drivers/md/md-llbitmap.c
> @@ -459,7 +459,8 @@ static struct page *llbitmap_read_page(struct llbitmap *llbitmap, int idx)
>         rdev_for_each(rdev, mddev) {
>                 sector_t sector;
>
> -               if (rdev->raid_disk < 0 || test_bit(Faulty, &rdev->flags))
> +               if (rdev->raid_disk < 0 || test_bit(Faulty, &rdev->flags) ||
> +                   !test_bit(In_sync, &rdev->flags))
>                         continue;
>
>                 sector = mddev->bitmap_info.offset +
> --
> 2.51.0
>
>

Reviewed-by: Xiao Ni <xni@xxxxxxxxxx>