Re: [ 122/184] ext4: Fix max file size and logical block counting

["Lukáš Czerner" <lczerner@redhat.com>]

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On Wed, 5 Jun 2013, Lukￜ Czerner wrote:

> Date: Wed, 5 Jun 2013 11:26:55 +0200 (CEST)
> From: Lukￜ Czerner <lczerner@redhat.com>
> To: Willy Tarreau <w@1wt.eu>
> Cc: linux-kernel@vger.kernel.org, stable@vger.kernel.org,
>     Theodore Tso <tytso@mit.edu>
> Subject: Re: [ 122/184] ext4: Fix max file size and logical block counting
> 
> On Tue, 4 Jun 2013, Willy Tarreau wrote:
> 
> > Date: Tue, 04 Jun 2013 19:23:32 +0200
> > From: Willy Tarreau <w@1wt.eu>
> > To: linux-kernel@vger.kernel.org, stable@vger.kernel.org
> > Cc: Lukas Czerner <lczerner@redhat.com>, Theodore Tso <tytso@mit.edu>,
> >     Willy Tarreau <w@1wt.eu>
> > Subject: [ 122/184] ext4: Fix max file size and logical block counting
> > 
> > 2.6.32-longterm review patch.  If anyone has any objections, please let me know.
> 
> Now it looks like we could get rid of this thing in e2fsprogs as
> well. As well as remove the remaining bits from kernel.
> What do you think Ted ?

Oops, this is not the commit I was looking for. Sorry for the noise!

-Lukas

> 
> -Lukas
> 
> > 
> > ------------------
> >  of extent format file
> > 
> > From: Lukas Czerner <lczerner@redhat.com>
> > 
> > commit f17722f917b2f21497deb6edc62fb1683daa08e6 upstream
> > 
> > Kazuya Mio reported that he was able to hit BUG_ON(next == lblock)
> > in ext4_ext_put_gap_in_cache() while creating a sparse file in extent
> > format and fill the tail of file up to its end. We will hit the BUG_ON
> > when we write the last block (2^32-1) into the sparse file.
> > 
> > The root cause of the problem lies in the fact that we specifically set
> > s_maxbytes so that block at s_maxbytes fit into on-disk extent format,
> > which is 32 bit long. However, we are not storing start and end block
> > number, but rather start block number and length in blocks. It means
> > that in order to cover extent from 0 to EXT_MAX_BLOCK we need
> > EXT_MAX_BLOCK+1 to fit into len (because we counting block 0 as well) -
> > and it does not.
> > 
> > The only way to fix it without changing the meaning of the struct
> > ext4_extent members is, as Kazuya Mio suggested, to lower s_maxbytes
> > by one fs block so we can cover the whole extent we can get by the
> > on-disk extent format.
> > 
> > Also in many places EXT_MAX_BLOCK is used as length instead of maximum
> > logical block number as the name suggests, it is all a bit messy. So
> > this commit renames it to EXT_MAX_BLOCKS and change its usage in some
> > places to actually be maximum number of blocks in the extent.
> > 
> > The bug which this commit fixes can be reproduced as follows:
> > 
> >  dd if=/dev/zero of=/mnt/mp1/file bs=<blocksize> count=1 seek=$((2**32-2))
> >  sync
> >  dd if=/dev/zero of=/mnt/mp1/file bs=<blocksize> count=1 seek=$((2**32-1))
> > 
> > Reported-by: Kazuya Mio <k-mio@sx.jp.nec.com>
> > Signed-off-by: Lukas Czerner <lczerner@redhat.com>
> > Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> > [dannf: Applied the backport from RHEL6 to Debian's 2.6.32]
> > Signed-off-by: Willy Tarreau <w@1wt.eu>
> > ---
> >  fs/ext4/ext4_extents.h |  7 +++++--
> >  fs/ext4/extents.c      | 39 +++++++++++++++++++--------------------
> >  fs/ext4/move_extent.c  | 10 +++++-----
> >  fs/ext4/super.c        | 15 ++++++++++++---
> >  4 files changed, 41 insertions(+), 30 deletions(-)
> > 
> > diff --git a/fs/ext4/ext4_extents.h b/fs/ext4/ext4_extents.h
> > index bdb6ce7..24fa647 100644
> > --- a/fs/ext4/ext4_extents.h
> > +++ b/fs/ext4/ext4_extents.h
> > @@ -137,8 +137,11 @@ typedef int (*ext_prepare_callback)(struct inode *, struct ext4_ext_path *,
> >  #define EXT_BREAK      1
> >  #define EXT_REPEAT     2
> >  
> > -/* Maximum logical block in a file; ext4_extent's ee_block is __le32 */
> > -#define EXT_MAX_BLOCK	0xffffffff
> > +/*
> > + * Maximum number of logical blocks in a file; ext4_extent's ee_block is
> > + * __le32.
> > + */
> > +#define EXT_MAX_BLOCKS	0xffffffff
> >  
> >  /*
> >   * EXT_INIT_MAX_LEN is the maximum number of blocks we can have in an
> > diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> > index b4402c8..f4b471d 100644
> > --- a/fs/ext4/extents.c
> > +++ b/fs/ext4/extents.c
> > @@ -1331,7 +1331,7 @@ got_index:
> >  
> >  /*
> >   * ext4_ext_next_allocated_block:
> > - * returns allocated block in subsequent extent or EXT_MAX_BLOCK.
> > + * returns allocated block in subsequent extent or EXT_MAX_BLOCKS.
> >   * NOTE: it considers block number from index entry as
> >   * allocated block. Thus, index entries have to be consistent
> >   * with leaves.
> > @@ -1345,7 +1345,7 @@ ext4_ext_next_allocated_block(struct ext4_ext_path *path)
> >  	depth = path->p_depth;
> >  
> >  	if (depth == 0 && path->p_ext == NULL)
> > -		return EXT_MAX_BLOCK;
> > +		return EXT_MAX_BLOCKS;
> >  
> >  	while (depth >= 0) {
> >  		if (depth == path->p_depth) {
> > @@ -1362,12 +1362,12 @@ ext4_ext_next_allocated_block(struct ext4_ext_path *path)
> >  		depth--;
> >  	}
> >  
> > -	return EXT_MAX_BLOCK;
> > +	return EXT_MAX_BLOCKS;
> >  }
> >  
> >  /*
> >   * ext4_ext_next_leaf_block:
> > - * returns first allocated block from next leaf or EXT_MAX_BLOCK
> > + * returns first allocated block from next leaf or EXT_MAX_BLOCKS
> >   */
> >  static ext4_lblk_t ext4_ext_next_leaf_block(struct inode *inode,
> >  					struct ext4_ext_path *path)
> > @@ -1379,7 +1379,7 @@ static ext4_lblk_t ext4_ext_next_leaf_block(struct inode *inode,
> >  
> >  	/* zero-tree has no leaf blocks at all */
> >  	if (depth == 0)
> > -		return EXT_MAX_BLOCK;
> > +		return EXT_MAX_BLOCKS;
> >  
> >  	/* go to index block */
> >  	depth--;
> > @@ -1392,7 +1392,7 @@ static ext4_lblk_t ext4_ext_next_leaf_block(struct inode *inode,
> >  		depth--;
> >  	}
> >  
> > -	return EXT_MAX_BLOCK;
> > +	return EXT_MAX_BLOCKS;
> >  }
> >  
> >  /*
> > @@ -1572,13 +1572,13 @@ unsigned int ext4_ext_check_overlap(struct inode *inode,
> >  	 */
> >  	if (b2 < b1) {
> >  		b2 = ext4_ext_next_allocated_block(path);
> > -		if (b2 == EXT_MAX_BLOCK)
> > +		if (b2 == EXT_MAX_BLOCKS)
> >  			goto out;
> >  	}
> >  
> >  	/* check for wrap through zero on extent logical start block*/
> >  	if (b1 + len1 < b1) {
> > -		len1 = EXT_MAX_BLOCK - b1;
> > +		len1 = EXT_MAX_BLOCKS - b1;
> >  		newext->ee_len = cpu_to_le16(len1);
> >  		ret = 1;
> >  	}
> > @@ -1654,7 +1654,7 @@ repeat:
> >  	fex = EXT_LAST_EXTENT(eh);
> >  	next = ext4_ext_next_leaf_block(inode, path);
> >  	if (le32_to_cpu(newext->ee_block) > le32_to_cpu(fex->ee_block)
> > -	    && next != EXT_MAX_BLOCK) {
> > +	    && next != EXT_MAX_BLOCKS) {
> >  		ext_debug("next leaf block - %d\n", next);
> >  		BUG_ON(npath != NULL);
> >  		npath = ext4_ext_find_extent(inode, next, NULL);
> > @@ -1772,7 +1772,7 @@ int ext4_ext_walk_space(struct inode *inode, ext4_lblk_t block,
> >  	BUG_ON(func == NULL);
> >  	BUG_ON(inode == NULL);
> >  
> > -	while (block < last && block != EXT_MAX_BLOCK) {
> > +	while (block < last && block != EXT_MAX_BLOCKS) {
> >  		num = last - block;
> >  		/* find extent for this block */
> >  		down_read(&EXT4_I(inode)->i_data_sem);
> > @@ -1900,7 +1900,7 @@ ext4_ext_put_gap_in_cache(struct inode *inode, struct ext4_ext_path *path,
> >  	if (ex == NULL) {
> >  		/* there is no extent yet, so gap is [0;-] */
> >  		lblock = 0;
> > -		len = EXT_MAX_BLOCK;
> > +		len = EXT_MAX_BLOCKS;
> >  		ext_debug("cache gap(whole file):");
> >  	} else if (block < le32_to_cpu(ex->ee_block)) {
> >  		lblock = block;
> > @@ -2145,8 +2145,8 @@ ext4_ext_rm_leaf(handle_t *handle, struct inode *inode,
> >  		path[depth].p_ext = ex;
> >  
> >  		a = ex_ee_block > start ? ex_ee_block : start;
> > -		b = ex_ee_block + ex_ee_len - 1 < EXT_MAX_BLOCK ?
> > -			ex_ee_block + ex_ee_len - 1 : EXT_MAX_BLOCK;
> > +		b = ex_ee_block + ex_ee_len - 1 < EXT_MAX_BLOCKS ?
> > +			ex_ee_block + ex_ee_len - 1 : EXT_MAX_BLOCKS;
> >  
> >  		ext_debug("  border %u:%u\n", a, b);
> >  
> > @@ -3783,15 +3783,14 @@ static int ext4_ext_fiemap_cb(struct inode *inode, struct ext4_ext_path *path,
> >  		flags |= FIEMAP_EXTENT_UNWRITTEN;
> >  
> >  	/*
> > -	 * If this extent reaches EXT_MAX_BLOCK, it must be last.
> > +	 * If this extent reaches EXT_MAX_BLOCKS, it must be last.
> >  	 *
> > -	 * Or if ext4_ext_next_allocated_block is EXT_MAX_BLOCK,
> > +	 * Or if ext4_ext_next_allocated_block is EXT_MAX_BLOCKS,
> >  	 * this also indicates no more allocated blocks.
> >  	 *
> > -	 * XXX this might miss a single-block extent at EXT_MAX_BLOCK
> >  	 */
> > -	if (ext4_ext_next_allocated_block(path) == EXT_MAX_BLOCK ||
> > -	    newex->ec_block + newex->ec_len - 1 == EXT_MAX_BLOCK) {
> > +	if (ext4_ext_next_allocated_block(path) == EXT_MAX_BLOCKS ||
> > +	    newex->ec_block + newex->ec_len == EXT_MAX_BLOCKS) {
> >  		loff_t size = i_size_read(inode);
> >  		loff_t bs = EXT4_BLOCK_SIZE(inode->i_sb);
> >  
> > @@ -3871,8 +3870,8 @@ int ext4_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
> >  
> >  		start_blk = start >> inode->i_sb->s_blocksize_bits;
> >  		last_blk = (start + len - 1) >> inode->i_sb->s_blocksize_bits;
> > -		if (last_blk >= EXT_MAX_BLOCK)
> > -			last_blk = EXT_MAX_BLOCK-1;
> > +		if (last_blk >= EXT_MAX_BLOCKS)
> > +			last_blk = EXT_MAX_BLOCKS-1;
> >  		len_blks = ((ext4_lblk_t) last_blk) - start_blk + 1;
> >  
> >  		/*
> > diff --git a/fs/ext4/move_extent.c b/fs/ext4/move_extent.c
> > index a73ed78..fe81390 100644
> > --- a/fs/ext4/move_extent.c
> > +++ b/fs/ext4/move_extent.c
> > @@ -1001,12 +1001,12 @@ mext_check_arguments(struct inode *orig_inode,
> >  		return -EINVAL;
> >  	}
> >  
> > -	if ((orig_start > EXT_MAX_BLOCK) ||
> > -	    (donor_start > EXT_MAX_BLOCK) ||
> > -	    (*len > EXT_MAX_BLOCK) ||
> > -	    (orig_start + *len > EXT_MAX_BLOCK))  {
> > +	if ((orig_start >= EXT_MAX_BLOCKS) ||
> > +	    (donor_start >= EXT_MAX_BLOCKS) ||
> > +	    (*len > EXT_MAX_BLOCKS) ||
> > +	    (orig_start + *len >= EXT_MAX_BLOCKS))  {
> >  		ext4_debug("ext4 move extent: Can't handle over [%u] blocks "
> > -			"[ino:orig %lu, donor %lu]\n", EXT_MAX_BLOCK,
> > +			"[ino:orig %lu, donor %lu]\n", EXT_MAX_BLOCKS,
> >  			orig_inode->i_ino, donor_inode->i_ino);
> >  		return -EINVAL;
> >  	}
> > diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> > index f1e7077..3ce77c5 100644
> > --- a/fs/ext4/super.c
> > +++ b/fs/ext4/super.c
> > @@ -1975,6 +1975,12 @@ static void ext4_orphan_cleanup(struct super_block *sb,
> >   * in the vfs.  ext4 inode has 48 bits of i_block in fsblock units,
> >   * so that won't be a limiting factor.
> >   *
> > + * However there is other limiting factor. We do store extents in the form
> > + * of starting block and length, hence the resulting length of the extent
> > + * covering maximum file size must fit into on-disk format containers as
> > + * well. Given that length is always by 1 unit bigger than max unit (because
> > + * we count 0 as well) we have to lower the s_maxbytes by one fs block.
> > + *
> >   * Note, this does *not* consider any metadata overhead for vfs i_blocks.
> >   */
> >  static loff_t ext4_max_size(int blkbits, int has_huge_files)
> > @@ -1996,10 +2002,13 @@ static loff_t ext4_max_size(int blkbits, int has_huge_files)
> >  		upper_limit <<= blkbits;
> >  	}
> >  
> > -	/* 32-bit extent-start container, ee_block */
> > -	res = 1LL << 32;
> > +	/*
> > +	 * 32-bit extent-start container, ee_block. We lower the maxbytes
> > +	 * by one fs block, so ee_len can cover the extent of maximum file
> > +	 * size
> > +	 */
> > +	res = (1LL << 32) - 1;
> >  	res <<= blkbits;
> > -	res -= 1;
> >  
> >  	/* Sanity check against vm- & vfs- imposed limits */
> >  	if (res > upper_limit)
> > 
>