linux-ext4 - Re: [PATCH v2] ext4: fix initialization of UNINIT bitmap blocks

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Message-ID: <20080915133604.GA6548@skywalker>
Date:	Mon, 15 Sep 2008 19:06:04 +0530
From:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>
To:	Frédéric Bohé <frederic.bohe@...l.net>
Cc:	"linux-ext4@...r.kernel.org" <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] ext4: fix initialization of UNINIT bitmap blocks

On Mon, Sep 15, 2008 at 02:16:47PM +0200, Frédéric Bohé wrote:
> From: Frederic Bohe <frederic.bohe@...l.net>
> 
> Do not rely on buffer head's uptodate flag to initialize
> uninitialized bitmap blocks.
> 
> Signed-off-by: Frederic Bohe <frederic.bohe@...l.net>
> ---
> Sorry there was a copy/paste error in the previous mail !
> 
> This patch makes sure to initialize uninited bitmap blocks.
> These are two test cases where bugs appear because of uninited blocks :
> 
> 1- This test case lead to uninited block bitmap and an error message
> from the mballocator during the second dd.
> 
> dd if=/dev/urandom of=/dev/md0 bs=1M count=300
> mkfs.ext4 -t ext4dev /dev/md0 1G
> mount -t ext4dev /dev/md0 /mnt/test
> resize2fs /dev/md0 2G
> dd if=/dev/zero of=/mnt/test/dummy bs=1M count=1500
> 
> Note that the first dd is to make sure we have random garbage in the
> uninited blocks. If not, you could miss the issue depending what was in
> those blocks before running mkfs.
> 
> 2- This test case lead to uninited inode bitmap blocks, making it
> impossible to use all the inodes of the fs.
> 
> dd if=/dev/urandom of=/dev/md0 bs=1M count=20
> mkfs.ext4 -t ext4dev /dev/md0 10M
> mount -t ext4dev /dev/md0 /mnt/test
> resize2fs /dev/md0 20M
> for i in $(seq 1 3800); do touch /mnt/test/file${i} 2>&1; done
> 
>  balloc.c  |    4 +++-
>  ialloc.c  |    4 +++-
>  mballoc.c |    4 +++-
>  3 files changed, 9 insertions(+), 3 deletions(-)
> 
> Index: linux-2.6.27-rc5+patch_queue/fs/ext4/balloc.c
> ===================================================================
> --- linux-2.6.27-rc5+patch_queue.orig/fs/ext4/balloc.c	2008-09-15 10:59:27.000000000 +0200
> +++ linux-2.6.27-rc5+patch_queue/fs/ext4/balloc.c	2008-09-15 14:03:04.000000000 +0200
> @@ -318,9 +318,11 @@ ext4_read_block_bitmap(struct super_bloc
>  			    block_group, bitmap_blk);
>  		return NULL;
>  	}
> -	if (bh_uptodate_or_lock(bh))
> +	if (buffer_uptodate(bh) &&
> +	    !(desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))
>  		return bh;
> 
> +	lock_buffer(bh);
>  	spin_lock(sb_bgl_lock(EXT4_SB(sb), block_group));
>  	if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
>  		ext4_init_block_bitmap(sb, bh, block_group, desc);

Why ? I guess resize should mark those buffer_heads as not uptodate so
that we do a reinit of block bitmap again later. The above change will
result in calling ext4_init_block_bitmap everytime we do a
read_block_bitmap on an uninit group




> Index: linux-2.6.27-rc5+patch_queue/fs/ext4/ialloc.c
> ===================================================================
> --- linux-2.6.27-rc5+patch_queue.orig/fs/ext4/ialloc.c	2008-09-15 10:59:27.000000000 +0200
> +++ linux-2.6.27-rc5+patch_queue/fs/ext4/ialloc.c	2008-09-15 11:12:16.000000000 +0200
> @@ -115,9 +115,11 @@ ext4_read_inode_bitmap(struct super_bloc
>  			    block_group, bitmap_blk);
>  		return NULL;
>  	}
> -	if (bh_uptodate_or_lock(bh))
> +	if (buffer_uptodate(bh) &&
> +	    !(desc->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)))
>  		return bh;
> 
> +	lock_buffer(bh);
>  	spin_lock(sb_bgl_lock(EXT4_SB(sb), block_group));
>  	if (desc->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
>  		ext4_init_inode_bitmap(sb, bh, block_group, desc);
> Index: linux-2.6.27-rc5+patch_queue/fs/ext4/mballoc.c
> ===================================================================
> --- linux-2.6.27-rc5+patch_queue.orig/fs/ext4/mballoc.c	2008-09-15 10:59:27.000000000 +0200
> +++ linux-2.6.27-rc5+patch_queue/fs/ext4/mballoc.c	2008-09-15 14:02:44.000000000 +0200
> @@ -785,9 +785,11 @@ static int ext4_mb_init_cache(struct pag
>  		if (bh[i] == NULL)
>  			goto out;
> 
> -		if (bh_uptodate_or_lock(bh[i]))
> +		if (buffer_uptodate(bh[i]) &&
> +		    !(desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)))
>  			continue;
> 
> +		lock_buffer(bh[i]);
>  		spin_lock(sb_bgl_lock(EXT4_SB(sb), first_group + i));
>  		if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
>  			ext4_init_block_bitmap(sb, bh[i],
> 

-aneesh
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