On Wed, Sep 11 2019 at 7:31am -0400,
Ming Lei <ming.lei@xxxxxxxxxx> wrote:
> Unit of 'chunk_size' is byte, instead of sector, so fix it.
>
> Without this fix, too big max_discard_sectors is applied on the request queue
> of dm-raid, finally raid code has to split the bio again.
>
> This re-split done by raid causes the following nested clone_endio:
>
> 1) one big bio 'A' is submitted to dm queue, and served as the original
> bio
>
> 2) one new bio 'B' is cloned from the original bio 'A', and .map()
> is run on this bio of 'B', and B's original bio points to 'A'
>
> 3) raid code sees that 'B' is too big, and split 'B' and re-submit
> the remainded part of 'B' to dm-raid queue via generic_make_request().
>
> 4) now dm will hanlde 'B' as new original bio, then allocate a new
> clone bio of 'C' and run .map() on 'C'. Meantime C's original bio
> points to 'B'.
>
> 5) suppose now 'C' is completed by raid direclty, then the following
> clone_endio() is called recursively:
>
> clone_endio(C)
> ->clone_endio(B) #B is original bio of 'C'
> ->bio_endio(A)
>
> 'A' can be big enough to make handreds of nested clone_endio(), then
> stack can be corrupted easily.
>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> V2:
> - fix commit log a bit
>
> drivers/md/dm-raid.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/md/dm-raid.c b/drivers/md/dm-raid.c
> index 8a60a4a070ac..c26aa4e8207a 100644
> --- a/drivers/md/dm-raid.c
> +++ b/drivers/md/dm-raid.c
> @@ -3749,7 +3749,7 @@ static void raid_io_hints(struct dm_target *ti, struct queue_limits *limits)
> */
> if (rs_is_raid1(rs) || rs_is_raid10(rs)) {
> limits->discard_granularity = chunk_size;
> - limits->max_discard_sectors = chunk_size;
> + limits->max_discard_sectors = chunk_size >> 9;
> }
> }
>
> --
> 2.20.1
>
Thanks a lot Ming! But oof, really embarassing oversight on my part!
FYI, I added a "Fixes:" tag to the commit header and switched to
shifting by SECTOR_SHIFT instead of 9, staged commit for 5.4 is here:
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-5.4&id=509818079bf1fefff4ed02d6a1b994e20efc0480
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