Re: [PATCH v2 3/5] md: add fallback to correct bitmap_ops on version mismatch

[Yu Kuai]

Hi,

在 2026/3/10 9:06, Xiao Ni 写道:
> On Mon, Feb 23, 2026 at 10:43 AM Yu Kuai <yukuai@xxxxxxxxx> wrote:
>> If default bitmap version and on-disk version doesn't match, and mdadm
>> is not the latest version to set bitmap_type, set bitmap_ops based on
>> the disk version.
> Hi Kuai
>
> How can I do test to check if this patch works?
>
> 1. Create array with llbitmap
> 2. Stop the array
> 3. uninstall mdadm with llbitmap support and install mdadm without llbitmap
> 4. assemble the array

At first, my colleague met this problem during power off and reboot test, however
I can't reproduce this, after adding some debug info, I'm quite sure this is still
an mdadm issue, that somewhere write llbitmap to sysfs bitmap_type file is missing.

Also, this way can be check as well if this patch works.

>
> Is it the case you want to fix?
>
> Regards
> Xiao
>> Signed-off-by: Yu Kuai <yukuai@xxxxxxxxx>
>> ---
>>   drivers/md/md.c | 111 +++++++++++++++++++++++++++++++++++++++++++++++-
>>   1 file changed, 110 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/md/md.c b/drivers/md/md.c
>> index 72a1c7267851..245785ad0ffd 100644
>> --- a/drivers/md/md.c
>> +++ b/drivers/md/md.c
>> @@ -6447,15 +6447,124 @@ static void md_safemode_timeout(struct timer_list *t)
>>
>>   static int start_dirty_degraded;
>>
>> +/*
>> + * Read bitmap superblock and return the bitmap_id based on disk version.
>> + * This is used as fallback when default bitmap version and on-disk version
>> + * doesn't match, and mdadm is not the latest version to set bitmap_type.
>> + */
>> +static enum md_submodule_id md_bitmap_get_id_from_sb(struct mddev *mddev)
>> +{
>> +       struct md_rdev *rdev;
>> +       struct page *sb_page;
>> +       bitmap_super_t *sb;
>> +       enum md_submodule_id id = ID_BITMAP_NONE;
>> +       sector_t sector;
>> +       u32 version;
>> +
>> +       if (!mddev->bitmap_info.offset)
>> +               return ID_BITMAP_NONE;
>> +
>> +       sb_page = alloc_page(GFP_KERNEL);
>> +       if (!sb_page) {
>> +               pr_warn("md: %s: failed to allocate memory for bitmap\n",
>> +                       mdname(mddev));
>> +               return ID_BITMAP_NONE;
>> +       }
>> +
>> +       sector = mddev->bitmap_info.offset;
>> +
>> +       rdev_for_each(rdev, mddev) {
>> +               u32 iosize;
>> +
>> +               if (!test_bit(In_sync, &rdev->flags) ||
>> +                   test_bit(Faulty, &rdev->flags) ||
>> +                   test_bit(Bitmap_sync, &rdev->flags))
>> +                       continue;
>> +
>> +               iosize = roundup(sizeof(bitmap_super_t),
>> +                                bdev_logical_block_size(rdev->bdev));
>> +               if (sync_page_io(rdev, sector, iosize, sb_page, REQ_OP_READ,
>> +                                true))
>> +                       goto read_ok;
>> +       }
>> +       pr_warn("md: %s: failed to read bitmap from any device\n",
>> +               mdname(mddev));
>> +       goto out;
>> +
>> +read_ok:
>> +       sb = kmap_local_page(sb_page);
>> +       if (sb->magic != cpu_to_le32(BITMAP_MAGIC)) {
>> +               pr_warn("md: %s: invalid bitmap magic 0x%x\n",
>> +                       mdname(mddev), le32_to_cpu(sb->magic));
>> +               goto out_unmap;
>> +       }
>> +
>> +       version = le32_to_cpu(sb->version);
>> +       switch (version) {
>> +       case BITMAP_MAJOR_LO:
>> +       case BITMAP_MAJOR_HI:
>> +       case BITMAP_MAJOR_CLUSTERED:
>> +               id = ID_BITMAP;
>> +               break;
>> +       case BITMAP_MAJOR_LOCKLESS:
>> +               id = ID_LLBITMAP;
>> +               break;
>> +       default:
>> +               pr_warn("md: %s: unknown bitmap version %u\n",
>> +                       mdname(mddev), version);
>> +               break;
>> +       }
>> +
>> +out_unmap:
>> +       kunmap_local(sb);
>> +out:
>> +       __free_page(sb_page);
>> +       return id;
>> +}
>> +
>>   static int md_bitmap_create(struct mddev *mddev)
>>   {
>> +       enum md_submodule_id orig_id = mddev->bitmap_id;
>> +       enum md_submodule_id sb_id;
>> +       int err;
>> +
>>          if (mddev->bitmap_id == ID_BITMAP_NONE)
>>                  return -EINVAL;
>>
>>          if (!mddev_set_bitmap_ops(mddev))
>>                  return -ENOENT;
>>
>> -       return mddev->bitmap_ops->create(mddev);
>> +       err = mddev->bitmap_ops->create(mddev);
>> +       if (!err)
>> +               return 0;
>> +
>> +       /*
>> +        * Create failed, if default bitmap version and on-disk version
>> +        * doesn't match, and mdadm is not the latest version to set
>> +        * bitmap_type, set bitmap_ops based on the disk version.
>> +        */
>> +       mddev_clear_bitmap_ops(mddev);
>> +
>> +       sb_id = md_bitmap_get_id_from_sb(mddev);
>> +       if (sb_id == ID_BITMAP_NONE || sb_id == orig_id)
>> +               return err;
>> +
>> +       pr_info("md: %s: bitmap version mismatch, switching from %d to %d\n",
>> +               mdname(mddev), orig_id, sb_id);
>> +
>> +       mddev->bitmap_id = sb_id;
>> +       if (!mddev_set_bitmap_ops(mddev)) {
>> +               mddev->bitmap_id = orig_id;
>> +               return -ENOENT;
>> +       }
>> +
>> +       err = mddev->bitmap_ops->create(mddev);
>> +       if (err) {
>> +               mddev_clear_bitmap_ops(mddev);
>> +               mddev->bitmap_id = orig_id;
>> +       }
>> +
>> +       return err;
>>   }
>>
>>   static void md_bitmap_destroy(struct mddev *mddev)
>> --
>> 2.51.0
>>
>>
-- 
Thansk,
Kuai