Patch to fix boot from RAID-1 partitioned arrays

[Geoff Back <geoff@demonlair.co.uk>]

Good morning.

I have had problems in all recent kernels with booting directly from MD 
RAID-1 partitioned arrays (i.e. without using an initrd).
All the usual requirements - building md and raid1 into the kernel, 
correct partition types, etc - are correct.

Deep investigation has led me to conclude that the issue is caused by 
boot-time assembly of the array not reading the partition table, meaning 
that the partitions are not visible and cannot be mounted as root 
filesystem.

The change to drivers/md/md-autodetect.c in commit 
a1d6bc018911390274e3904bdd28240cd96ddc54 appears to be related, although 
this only covers some cases not all, so I have not been able to 
determine exactly what commit led to this problem.

I have implemented a patch that causes the partition table to be read 
immediately after the array is started, for the two boot-time assembly 
paths (from autodetect with raid=part, and from assembly with md=d0,...) 
which is included below.

Regards,

Geoff.

diff -Naur linux-5.12.2.orig/drivers/md/md-autodetect.c 
linux-5.12.2/drivers/md/md-autodetect.c
--- linux-5.12.2.orig/drivers/md/md-autodetect.c    2021-05-12 
09:14:07.096442083 +0100
+++ linux-5.12.2/drivers/md/md-autodetect.c    2021-05-12 
09:22:07.734653840 +0100
@@ -232,8 +232,24 @@
      mddev_unlock(mddev);
  out_blkdev_put:
      blkdev_put(bdev, FMODE_READ);
-}

+    /*
+     * Need to force read of partition table in order for partitioned
+     * arrays to be bootable.  Deliberately done after all cleanup,
+     * and only for successfully loaded arrays.
+     */
+    if (err == 0)
+    {
+        struct block_device *bd;
+
+        bd = blkdev_get_by_dev(mdev, FMODE_READ, NULL);
+        if (IS_ERR(bd))
+            pr_err("md: failed to get md device\n");
+        else
+            blkdev_put(bd, FMODE_READ);
+    }
+}
+
  static int __init raid_setup(char *str)
  {
      int len, pos;
diff -Naur linux-5.12.2.orig/drivers/md/md.c linux-5.12.2/drivers/md/md.c
--- linux-5.12.2.orig/drivers/md/md.c    2021-05-12 09:14:07.127441838 +0100
+++ linux-5.12.2/drivers/md/md.c    2021-05-12 09:34:26.960827487 +0100
@@ -6467,6 +6467,20 @@
          pr_warn("md: do_md_run() returned %d\n", err);
          do_md_stop(mddev, 0, NULL);
      }
+    else
+    {
+        /*
+         * Need to force read of partition table in order for partitioned
+         * arrays to be bootable.
+         */
+        struct block_device *bd;
+
+        bd = blkdev_get_by_dev(mdev, FMODE_READ, NULL);
+        if (IS_ERR(bd))
+            pr_err("md: failed to get md device\n");
+        else
+            blkdev_put(bd, FMODE_READ);
+    }
  }

  /*



-- 
Geoff Back
What if we're all just characters in someone's nightmares?