I don't understand how this works...
Can chunk_size_bytes be 0? If not, how is discard_granularity being set to 0?
I think also limits is local to the ti in question here, initialized
by blk_set_stacking_limits() via dm-table.c, and therefore has only
default values and not anything to do with the underlying queue. So
setting discard_granularity=max(discard_granularity, chunk_size_bytes)
doesn't seem like it should be working, unless I'm not understanding
what it's there for...
And shouldn't melding in the target's desired io_hints into the
existing queue limits be happening in blk_stack_limits() instead?
(Also, it does lcm_not_zero() for stacking granularity, instead of
max()...)
On Thu, Sep 24, 2020 at 12:29 PM Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
>
> This patch fixes a warning WARN_ON_ONCE(!q->limits.discard_granularity).
> The reason is that the function raid_io_hints overwrote
> limits->discard_granularity with zero. We need to properly stack the
> limits instead of overwriting them.
>
> Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
>
> ---
> drivers/md/dm-raid.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/drivers/md/dm-raid.c
> ===================================================================
> --- linux-2.6.orig/drivers/md/dm-raid.c 2020-09-24 18:16:45.000000000 +0200
> +++ linux-2.6/drivers/md/dm-raid.c 2020-09-24 18:16:45.000000000 +0200
> @@ -3734,8 +3734,8 @@ static void raid_io_hints(struct dm_targ
> * RAID0/4/5/6 don't and process large discard bios properly.
> */
> if (rs_is_raid1(rs) || rs_is_raid10(rs)) {
> - limits->discard_granularity = chunk_size_bytes;
> - limits->max_discard_sectors = rs->md.chunk_sectors;
> + limits->discard_granularity = max(limits->discard_granularity, chunk_size_bytes);
> + limits->max_discard_sectors = min_not_zero(limits->max_discard_sectors, (unsigned)rs->md.chunk_sectors);
> }
> }
>
>
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>
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