[PATCH stable/6.16-5.15] md: add check_new_feature module parameter

From: Li Nan <[email protected]>

commit 9c47127a807da3e36ce80f7c83a1134a291fc021 upstream.

Raid checks if pad3 is zero when loading superblock from disk. Arrays
created with new features may fail to assemble on old kernels as pad3
is used.

Add module parameter check_new_feature to bypass this check.

Link: https://lore.kernel.org/linux-raid/[email protected]
Signed-off-by: Li Nan <[email protected]>
Reviewed-by: Xiao Ni <[email protected]>
Signed-off-by: Yu Kuai <[email protected]>
[ Conflict in md.c, because of a difference in the context,
  introduced by commit 25db5f284fb8 ("md: add legacy_async_del_gendisk
  mode"), which is not in this version. The same lines can still be
  added at the same place. ]
Signed-off-by: Li Nan <[email protected]>
---
 drivers/md/md.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 0f41573fa9f5..4bcbd2ed439e 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -339,6 +339,7 @@ static int start_readonly;
  * so all the races disappear.
  */
 static bool create_on_open = true;
+static bool check_new_feature = true;
 
 /*
  * We have a system wide 'event count' that is incremented
@@ -1735,9 +1736,13 @@ static int super_1_load(struct md_rdev *rdev, struct md_rdev *refdev, int minor_
 	}
 	if (sb->pad0 ||
 	    sb->pad3[0] ||
-	    memcmp(sb->pad3, sb->pad3+1, sizeof(sb->pad3) - sizeof(sb->pad3[1])))
-		/* Some padding is non-zero, might be a new feature */
-		return -EINVAL;
+	    memcmp(sb->pad3, sb->pad3+1, sizeof(sb->pad3) - sizeof(sb->pad3[1]))) {
+		pr_warn("Some padding is non-zero on %pg, might be a new feature\n",
+			rdev->bdev);
+		if (check_new_feature)
+			return -EINVAL;
+		pr_warn("check_new_feature is disabled, data corruption possible\n");
+	}
 
 	rdev->preferred_minor = 0xffff;
 	rdev->data_offset = le64_to_cpu(sb->data_offset);
@@ -10422,6 +10427,7 @@ module_param_call(start_ro, set_ro, get_ro, NULL, S_IRUSR|S_IWUSR);
 module_param(start_dirty_degraded, int, S_IRUGO|S_IWUSR);
 module_param_call(new_array, add_named_array, NULL, NULL, S_IWUSR);
 module_param(create_on_open, bool, S_IRUSR|S_IWUSR);
+module_param(check_new_feature, bool, 0600);
 
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("MD RAID framework");
-- 
2.39.2