Re: [PATCH] Enable loading of bitmaps for dm-md-raid1.

[NeilBrown <neilb@suse.com>]

On Mon, 20 Jul 2015 12:06:28 -0500 Goldwyn Rodrigues <rgoldwyn@suse.de>
wrote:

> This is also a hack for systems with junk in the rest
> of the bitmap super (instead of zeroes) to boot. This is done by
> checking mddev->sync_super (which is exclusively set by dm-raid)
> is null.
> 
> These changes also include zeroing of most bitmap pages while
> allocating so we are sure that the junk is not coming from memory.
> 
> References: https://bugzilla.kernel.org/show_bug.cgi?id=100491
> 
> Signed-off-by: Neil Brown <neilb@suse.de>
> Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
> ---
> diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
> index 135a090..dfa5ef3 100644
> --- a/drivers/md/bitmap.c
> +++ b/drivers/md/bitmap.c
> @@ -494,7 +494,7 @@ static int bitmap_new_disk_sb(struct bitmap *bitmap)
>  	bitmap_super_t *sb;
>  	unsigned long chunksize, daemon_sleep, write_behind;
>  
> -	bitmap->storage.sb_page = alloc_page(GFP_KERNEL);
> +	bitmap->storage.sb_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
>  	if (bitmap->storage.sb_page == NULL)
>  		return -ENOMEM;
>  	bitmap->storage.sb_page->index = 0;
> @@ -541,6 +541,7 @@ static int bitmap_new_disk_sb(struct bitmap *bitmap)
>  	sb->state = cpu_to_le32(bitmap->flags);
>  	bitmap->events_cleared = bitmap->mddev->events;
>  	sb->events_cleared = cpu_to_le64(bitmap->mddev->events);
> +	bitmap->mddev->bitmap_info.nodes = 0;
>  
>  	kunmap_atomic(sb);
>  
> @@ -568,7 +569,7 @@ static int bitmap_read_sb(struct bitmap *bitmap)
>  		goto out_no_sb;
>  	}
>  	/* page 0 is the superblock, read it... */
> -	sb_page = alloc_page(GFP_KERNEL);
> +	sb_page = alloc_page(GFP_KERNEL | __GFP_ZERO);
>  	if (!sb_page)
>  		return -ENOMEM;
>  	bitmap->storage.sb_page = sb_page;
> @@ -611,8 +612,15 @@ re_read:
>  	daemon_sleep = le32_to_cpu(sb->daemon_sleep) * HZ;
>  	write_behind = le32_to_cpu(sb->write_behind);
>  	sectors_reserved = le32_to_cpu(sb->sectors_reserved);
> -	nodes = le32_to_cpu(sb->nodes);
> -	strlcpy(bitmap->mddev->bitmap_info.cluster_name, sb->cluster_name, 64);
> +	/* XXX: This is an ugly hack to ensure that we don't use clustering
> +	   in case dm-raid is in use and the nodes written in bitmap_sb
> +	   is erroneous.
> +	*/
> +	if (!bitmap->mddev->sync_super) {
> +		nodes = le32_to_cpu(sb->nodes);
> +		strlcpy(bitmap->mddev->bitmap_info.cluster_name,
> +				sb->cluster_name, 64);
> +	}
>  
>  	/* verify that the bitmap-specific fields are valid */
>  	if (sb->magic != cpu_to_le32(BITMAP_MAGIC))
> @@ -649,7 +657,7 @@ re_read:
>  			goto out;
>  		}
>  		events = le64_to_cpu(sb->events);
> -		if (!nodes && (events < bitmap->mddev->events)) {
> +		if (err == 0 && !nodes && (events < bitmap->mddev->events)) {
>  			printk(KERN_INFO
>  			       "%s: bitmap file is out of date (%llu < %llu) "
>  			       "-- forcing full recovery\n",
> diff --git a/drivers/md/md.c b/drivers/md/md.c
> index 4dbed4a..6bd8bc3 100644
> --- a/drivers/md/md.c
> +++ b/drivers/md/md.c
> @@ -7415,7 +7415,7 @@ int md_setup_cluster(struct mddev *mddev, int nodes)
>  	err = request_module("md-cluster");
>  	if (err) {
>  		pr_err("md-cluster module not found.\n");
> -		return err;
> +		return -ENOENT;
>  	}
>  
>  	spin_lock(&pers_lock);


Thanks... but I think this is about 3 patches.

The patch to md.c is because request_module() returns a status
different from what the documentation says.  And
Fixes: edb39c9deda8 ("Introduce md_cluster_operations to handle cluster functions")
(though it doesn't need to go to stable.

Adding "err == 0 &&' test is ... why is that?  It looks to me like
err == -EINVAL at that point, always.  Can you explain/

Using __GFP_ZERO in read_sb_page seems wrong and so misleading.

The rest are for the main bug you are trying to fix .. though I think
it could be described better.

-------------------
There is a bug that the bitmap superblock isn't initialised properly for
dm-raid, so a new field can have garbage in new fields.
(dm-raid does initialisation in the kernel - md initialised the
superblock in mdadm).
This means that for dm-raid we cannot currently trust the new ->nodes
field.
So:
 - use __GFP_ZERO to initialise the superblock properly for all new
   arrays
 - initialise all field in bitmap_info in bitmap_new_disk_sb
 - ignore ->nodes for dm arrays (yes, this is a hack)
-----------------

Could you make it 3 patches for me please?

Thanks,
NeilBrown