Hi David and Laurence,
On Tue, Nov 28, 2023 at 10:13 AM David Jeffery <djeffery@xxxxxxxxxx> wrote:
>
> During a reshape or a RAID6 array such as expanding by adding an additional
> disk, I/Os to the region of the array which have not yet been reshaped can
> stall indefinitely. This is from errors in the stripe_ahead_of_reshape
> function causing md to think the I/O is to a region in the actively
> undergoing the reshape.
>
> stripe_ahead_of_reshape fails to account for the q disk having a sector
> value of 0. By not excluding the q disk from the for loop, raid6 will always
> generate a min_sector value of 0, causing a return value which stalls.
>
> The function's max_sector calculation also uses min() when it should use
> max(), causing the max_sector value to always be 0. During a backwards
> rebuild this can cause the opposite problem where it allows I/O to advance
> when it should wait.
>
> Fixing these errors will allow safe I/O to advance in a timely manner and
> delay only I/O which is unsafe due to stripes in the middle of undergoing
> the reshape.
>
> Fixes: 486f60558607 ("md/raid5: Check all disks in a stripe_head for reshape progress")
> Signed-off-by: David Jeffery <djeffery@xxxxxxxxxx>
> Tested-by: Laurence Oberman <loberman@xxxxxxxxxx>
Thanks for the fix!
Can we add a test to mdadm/tests to cover this case? (Not sure how reliable
the test will be).
Song
> ---
> drivers/md/raid5.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
> index dc031d42f53b..26e1e8a5e941 100644
> --- a/drivers/md/raid5.c
> +++ b/drivers/md/raid5.c
> @@ -5892,11 +5892,11 @@ static bool stripe_ahead_of_reshape(struct mddev *mddev, struct r5conf *conf,
> int dd_idx;
>
> for (dd_idx = 0; dd_idx < sh->disks; dd_idx++) {
> - if (dd_idx == sh->pd_idx)
> + if (dd_idx == sh->pd_idx || dd_idx == sh->qd_idx)
> continue;
>
> min_sector = min(min_sector, sh->dev[dd_idx].sector);
> - max_sector = min(max_sector, sh->dev[dd_idx].sector);
> + max_sector = max(max_sector, sh->dev[dd_idx].sector);
> }
>
> spin_lock_irq(&conf->device_lock);
> --
> 2.43.0
>
>
