[PATCH] btrfs: scrub: use do_div() for 64-by-32 division

[Adam Borowski <kilobyte@angband.pl>]

Unbreaks ARM and possibly other 32-bit architectures.

Fixes: 7d0ef8b4d: Btrfs: update scrub_parity to use u64 stripe_len
Reported-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Adam Borowski <kilobyte@angband.pl>
---
You'd probably want to squash this with Liu's commit, to be nice to future
bisects.

Tested on amd64 where all is fine, and on arm (Odroid-U2) where scrub
sometimes works, but, like most operations, randomly dies with some badness
that doesn't look related: io_schedule, kunmap_high.  That badness wasn't
there in 4.11-rc5, needs investigating, but since it's not connected to our
issue at hand, I consider this patch sort-of tested.

 fs/btrfs/scrub.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index b6fe1cd08048..95372e3679f3 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -2407,7 +2407,7 @@ static inline void __scrub_mark_bitmap(struct scrub_parity *sparity,
 
 	start -= sparity->logic_start;
 	start = div64_u64_rem(start, sparity->stripe_len, &offset);
-	offset /= sectorsize;
+	do_div(offset, sectorsize);
 	nsectors = (int)len / sectorsize;
 
 	if (offset + nsectors <= sparity->nsectors) {
-- 
2.11.0