On Thu, Sep 24 2020 at 12:26pm -0400,
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);
> }
> }
>
OK, but how is it that chunk_size_bytes is 0? Oh, raid1 doesn't have a
chunksize does it!?
Relative to MD raid0 and raid10: they don't have dm-stripe like
optimization to handle large discards. So stacking up larger discard
limits (that span multiple chunks) is a non-starter right?
Like dm-raid.c, raid10.c does explicitly set max_discard_sectors to
mddev->chunk_sectors. But it (mistakenly IMHO) just accepts stackd up
discard_granularity.
Looking at raid1.c I see MD is just stacking up the limits without
modification. Maybe dm-raid.c shouldn't be changing these limits at all
for raid1 (just use what was already stacked)?
WAIT... Could it be that raid_io_hints _really_ meant to special case
raid0 and raid10 -- due to their striping/splitting requirements!?
So, not raid1 but raid0?
E.g.:
diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
index 56b723d012ac..6dca932d6f1d 100644
--- a/drivers/md/dm-raid.c
+++ b/drivers/md/dm-raid.c
@@ -3730,10 +3730,10 @@ static void raid_io_hints(struct dm_target *ti,
struct queue_limits *limits)
blk_limits_io_opt(limits, chunk_size_bytes *
mddev_data_stripes(rs));
/*
- * RAID1 and RAID10 personalities require bio splitting,
- * RAID0/4/5/6 don't and process large discard bios properly.
+ * RAID0 and RAID10 personalities require bio splitting,
+ * RAID1/4/5/6 don't and process large discard bios properly.
*/
- if (rs_is_raid1(rs) || rs_is_raid10(rs)) {
+ if (rs_is_raid0(rs) || rs_is_raid10(rs)) {
limits->discard_granularity = chunk_size_bytes;
limits->max_discard_sectors = rs->md.chunk_sectors;
}
Mike
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