From 7e768532b2396bcb7fbf6f82384b85c0f1d2f197 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Tue, 25 May 2021 13:17:19 -0400
Subject: [PATCH] dm snapshot: properly fix a crash when an origin has no
 snapshots
Git-commit: 7e768532b2396bcb7fbf6f82384b85c0f1d2f197
Patch-mainline: v5.13-rc4
References: git-fixes

If an origin target has no snapshots, o->split_boundary is set to 0.
This causes BUG_ON(sectors <= 0) in block/bio.c:bio_split().

Fix this by initializing chunk_size, and in turn split_boundary, to
rounddown_pow_of_two(UINT_MAX) -- the largest power of two that fits
into "unsigned" type.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Coly Li <colyli@suse.de>

---
 drivers/md/dm-snap.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
index 75e59294ef77..751ec5ea1dbb 100644
--- a/drivers/md/dm-snap.c
+++ b/drivers/md/dm-snap.c
@@ -855,7 +855,7 @@ static int dm_add_exception(void *context, chunk_t old, chunk_t new)
 static uint32_t __minimum_chunk_size(struct origin *o)
 {
 	struct dm_snapshot *snap;
-	unsigned chunk_size = 0;
+	unsigned chunk_size = rounddown_pow_of_two(UINT_MAX);
 
 	if (o)
 		list_for_each_entry(snap, &o->snapshots, list)
-- 
2.35.3