md: add check_new_feature module parameter

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/20251103125757.1405796-5-linan666@huaweicloud.com
Signed-off-by: Li Nan <linan122@huawei.com>
Reviewed-by: Xiao Ni <xni@redhat.com>
Signed-off-by: Yu Kuai <yukuai@fnnas.com>

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 6193f5b2017d2216d3deca4d8a1a7f6b9895fcfd..9676e2477df6b35bfc30926d1156001fccab9dda 100644 (file)
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -339,6 +339,7 @@ static int start_readonly;
  */
 static bool create_on_open = true;
 static bool legacy_async_del_gendisk = true;
+static bool check_new_feature = true;
 
 /*
  * We have a system wide 'event count' that is incremented
@@ -1851,9 +1852,13 @@ 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);
@@ -10741,6 +10746,7 @@ 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(legacy_async_del_gendisk, bool, 0600);
+module_param(check_new_feature, bool, 0600);
 
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("MD RAID framework");