linux-kernel - [PATCH v9 4/5] md: add check_new

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Message-Id: <20251103125757.1405796-5-linan666@huaweicloud.com>
Date: Mon,  3 Nov 2025 20:57:56 +0800
From: linan666@...weicloud.com
To: corbet@....net,
	song@...nel.org,
	yukuai@...as.com,
	linan122@...wei.com,
	xni@...hat.com,
	hare@...e.de
Cc: linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	linux-raid@...r.kernel.org,
	linan666@...weicloud.com,
	yangerkun@...wei.com,
	yi.zhang@...wei.com
Subject: [PATCH v9 4/5] md: add check_new_feature module parameter

From: Li Nan <linan122@...wei.com>

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.

Signed-off-by: Li Nan <linan122@...wei.com>
---
 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 dffc6a482181..5921fb245bfa 100644
--- 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
@@ -1850,9 +1851,13 @@ 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);
@@ -10704,6 +10709,7 @@ 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");
-- 
2.39.2