Message-ID: <20140619174541.GB20194@quack.suse.cz>
Date:	Thu, 19 Jun 2014 19:45:41 +0200
From:	Jan Kara <jack@...e.cz>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	linux-ext4@...r.kernel.org, jack@...e.cz, stable@...r.kernel.org
Subject: Re: [PATCH] ext4: Fix punch hole on files with indirect mapping

On Thu 19-06-14 17:37:08, Lukas Czerner wrote:
> Currently punch hole code on files with direct/indirect mapping has some
> problems which may lead to a data loss. For example (from Jan Kara):
> 
> fallocate -n -p 10240000 4096
> 
> will punch the range 10240000 - 12632064 instead of the range 1024000 -
> 10244096.
> 
> Also the code is a bit weird and it's not using infrastructure provided
> by indirect.c, but rather creating it's own way.
> 
> This patch fixes the issues as well as making the operation to run 4
> times faster from my testing (punching out 60GB file). It uses similar
> approach used in ext4_ind_truncate() which takes advantage of
> ext4_free_branches() function.
> 
> Also rename the ext4_free_hole_blocks() to something more sensible, like
> the equivalent we have for extent mapped files. Call it
> ext4_ind_remove_space().
> 
> This has been tested mostly with fsx and some xfstests which are testing
> punch hole but does not require unwritten extents which are not
> supported with direct/indirect mapping. Not problems showed up even with
> 1024k block size.
  Hum, so I agree current code could use more of the truncate
infrastructure and be faster (especially the all_zeroes() checks are
presumably rather expensive) but frankly I find your version harder to read
than the original code was :-|. I'll try to read your code again with fresh
mind and either decide it's good enough that I can give my reviewed-by or
I can try to come up with something simpler...

								Honza

> CC: stable@...r.kernel.org
> Signed-off-by: Lukas Czerner <lczerner@...hat.com>
> ---
>  fs/ext4/ext4.h     |   4 +-
>  fs/ext4/indirect.c | 277 +++++++++++++++++++++++++++++++++++++++--------------
>  fs/ext4/inode.c    |   2 +-
>  3 files changed, 207 insertions(+), 76 deletions(-)
> 
> diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
> index 1479e2a..22113a73 100644
> --- a/fs/ext4/ext4.h
> +++ b/fs/ext4/ext4.h
> @@ -2145,8 +2145,8 @@ extern ssize_t ext4_ind_direct_IO(int rw, struct kiocb *iocb,
>  extern int ext4_ind_calc_metadata_amount(struct inode *inode, sector_t lblock);
>  extern int ext4_ind_trans_blocks(struct inode *inode, int nrblocks);
>  extern void ext4_ind_truncate(handle_t *, struct inode *inode);
> -extern int ext4_free_hole_blocks(handle_t *handle, struct inode *inode,
> -				 ext4_lblk_t first, ext4_lblk_t stop);
> +extern int ext4_ind_remove_space(handle_t *handle, struct inode *inode,
> +				 ext4_lblk_t start, ext4_lblk_t end);
>  
>  /* ioctl.c */
>  extern long ext4_ioctl(struct file *, unsigned int, unsigned long);
> diff --git a/fs/ext4/indirect.c b/fs/ext4/indirect.c
> index 594009f..adae538 100644
> --- a/fs/ext4/indirect.c
> +++ b/fs/ext4/indirect.c
> @@ -1291,89 +1291,220 @@ do_indirects:
>  	}
>  }
>  
> -static int free_hole_blocks(handle_t *handle, struct inode *inode,
> -			    struct buffer_head *parent_bh, __le32 *i_data,
> -			    int level, ext4_lblk_t first,
> -			    ext4_lblk_t count, int max)
> +/**
> + *	ext4_ind_remove_space - remove space from the range
> + *	@handle: JBD handle for this transaction
> + *	@inode:	inode we are dealing with
> + *	@start:	First block to remove
> + *	@end:	One block after the last block to remove (exclusive)
> + *
> + *	Free the blocks in the defined range (end is exclusive endpoint of
> + *	range). This is used by ext4_punch_hole().
> + */
> +int ext4_ind_remove_space(handle_t *handle, struct inode *inode,
> +			  ext4_lblk_t start, ext4_lblk_t end)
>  {
> -	struct buffer_head *bh = NULL;
> +	struct ext4_inode_info *ei = EXT4_I(inode);
> +	__le32 *i_data = ei->i_data;
>  	int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
> -	int ret = 0;
> -	int i, inc;
> -	ext4_lblk_t offset;
> -	__le32 blk;
> -
> -	inc = 1 << ((EXT4_BLOCK_SIZE_BITS(inode->i_sb) - 2) * level);
> -	for (i = 0, offset = 0; i < max; i++, i_data++, offset += inc) {
> -		if (offset >= count + first)
> -			break;
> -		if (*i_data == 0 || (offset + inc) <= first)
> -			continue;
> -		blk = *i_data;
> -		if (level > 0) {
> -			ext4_lblk_t first2;
> -			bh = sb_bread(inode->i_sb, le32_to_cpu(blk));
> -			if (!bh) {
> -				EXT4_ERROR_INODE_BLOCK(inode, le32_to_cpu(blk),
> -						       "Read failure");
> -				return -EIO;
> +	ext4_lblk_t offsets[4], offsets2[4];
> +	Indirect chain[4], chain2[4];
> +	Indirect *partial, *partial2;
> +	ext4_lblk_t max_block;
> +	__le32 nr = 0, nr2 = 0;
> +	int n = 0, n2 = 0;
> +	unsigned blocksize = inode->i_sb->s_blocksize;
> +
> +	max_block = (EXT4_SB(inode->i_sb)->s_bitmap_maxbytes + blocksize-1)
> +					>> EXT4_BLOCK_SIZE_BITS(inode->i_sb);
> +	if (end >= max_block)
> +		end = max_block;
> +	if ((start >= end) || (start > max_block))
> +		return 0;
> +
> +	n = ext4_block_to_path(inode, start, offsets, NULL);
> +	n2 = ext4_block_to_path(inode, end, offsets2, NULL);
> +
> +	BUG_ON(n > n2);
> +
> +	if ((n == 1) && (n == n2)) {
> +		/* We're punching only within direct block range */
> +		ext4_free_data(handle, inode, NULL, i_data + offsets[0],
> +			       i_data + offsets2[0]);
> +		return 0;
> +	} else if (n2 > n) {
> +		/*
> +		 * Start and end are on a different levels so we're going to
> +		 * free partial block at start, and partial block at end of
> +		 * the range. If there are some levels in between then
> +		 * do_indirects label will take care of that.
> +		 */
> +
> +		if (n == 1) {
> +			/*
> +			 * Start is at the direct block level, free
> +			 * everything to the end of the level.
> +			 */
> +			ext4_free_data(handle, inode, NULL, i_data + offsets[0],
> +				       i_data + EXT4_NDIR_BLOCKS);
> +			goto end_range;
> +		}
> +
> +
> +		partial = ext4_find_shared(inode, n, offsets, chain, &nr);
> +		if (nr) {
> +			if (partial == chain) {
> +				/* Shared branch grows from the inode */
> +				ext4_free_branches(handle, inode, NULL,
> +					   &nr, &nr+1, (chain+n-1) - partial);
> +				*partial->p = 0;
> +			} else {
> +				/* Shared branch grows from an indirect block */
> +				BUFFER_TRACE(partial->bh, "get_write_access");
> +				ext4_free_branches(handle, inode, partial->bh,
> +					partial->p,
> +					partial->p+1, (chain+n-1) - partial);
>  			}
> -			first2 = (first > offset) ? first - offset : 0;
> -			ret = free_hole_blocks(handle, inode, bh,
> -					       (__le32 *)bh->b_data, level - 1,
> -					       first2, count - offset,
> -					       inode->i_sb->s_blocksize >> 2);
> -			if (ret) {
> -				brelse(bh);
> -				goto err;
> +		}
> +
> +		/*
> +		 * Clear the ends of indirect blocks on the shared branch
> +		 * at the start of the range
> +		 */
> +		while (partial > chain) {
> +			ext4_free_branches(handle, inode, partial->bh,
> +				partial->p + 1,
> +				(__le32 *)partial->bh->b_data+addr_per_block,
> +				(chain+n-1) - partial);
> +			BUFFER_TRACE(partial->bh, "call brelse");
> +			brelse(partial->bh);
> +			partial--;
> +		}
> +
> +end_range:
> +		partial2 = ext4_find_shared(inode, n2, offsets2, chain2, &nr2);
> +		if (nr2) {
> +			if (partial2 == chain2) {
> +				/*
> +				 * Remember, end is exclusive so here we're at
> +				 * the start of the next level we're not going
> +				 * to free. Everything was covered by the start
> +				 * of the range.
> +				 */
> +				return 0;
> +			} else {
> +				/* Shared branch grows from an indirect block */
> +				partial2--;
>  			}
> +		} else {
> +			/*
> +			 * ext4_find_shared returns Indirect structure which
> +			 * points to the last element which should not be
> +			 * removed by truncate. But this is end of the range
> +			 * in punch_hole so we need to point to the next element
> +			 */
> +			partial2->p++;
>  		}
> -		if (level == 0 ||
> -		    (bh && all_zeroes((__le32 *)bh->b_data,
> -				      (__le32 *)bh->b_data + addr_per_block))) {
> -			ext4_free_data(handle, inode, parent_bh, &blk, &blk+1);
> -			*i_data = 0;
> +
> +		/*
> +		 * Clear the ends of indirect blocks on the shared branch
> +		 * at the end of the range
> +		 */
> +		while (partial2 > chain2) {
> +			ext4_free_branches(handle, inode, partial2->bh,
> +					   (__le32 *)partial2->bh->b_data,
> +					   partial2->p,
> +					   (chain2+n2-1) - partial2);
> +			BUFFER_TRACE(partial2->bh, "call brelse");
> +			brelse(partial2->bh);
> +			partial2--;
>  		}
> -		brelse(bh);
> -		bh = NULL;
> +		goto do_indirects;
>  	}
>  
> -err:
> -	return ret;
> -}
> -
> -int ext4_free_hole_blocks(handle_t *handle, struct inode *inode,
> -			  ext4_lblk_t first, ext4_lblk_t stop)
> -{
> -	int addr_per_block = EXT4_ADDR_PER_BLOCK(inode->i_sb);
> -	int level, ret = 0;
> -	int num = EXT4_NDIR_BLOCKS;
> -	ext4_lblk_t count, max = EXT4_NDIR_BLOCKS;
> -	__le32 *i_data = EXT4_I(inode)->i_data;
> -
> -	count = stop - first;
> -	for (level = 0; level < 4; level++, max *= addr_per_block) {
> -		if (first < max) {
> -			ret = free_hole_blocks(handle, inode, NULL, i_data,
> -					       level, first, count, num);
> -			if (ret)
> -				goto err;
> -			if (count > max - first)
> -				count -= max - first;
> -			else
> -				break;
> -			first = 0;
> -		} else {
> -			first -= max;
> +	/* Punch happened within the same level (n == n2) */
> +	partial = ext4_find_shared(inode, n, offsets, chain, &nr);
> +	partial2 = ext4_find_shared(inode, n2, offsets2, chain2, &nr2);
> +	/*
> +	 * ext4_find_shared returns Indirect structure which
> +	 * points to the last element which should not be
> +	 * removed by truncate. But this is end of the range
> +	 * in punch_hole so we need to point to the next element
> +	 */
> +	partial2->p++;
> +	while ((partial > chain) || (partial2 > chain2)) {
> +		/* We're at the same block, so we're almost finished */
> +		if ((partial->bh && partial2->bh) &&
> +		    (partial->bh->b_blocknr == partial2->bh->b_blocknr)) {
> +			if ((partial > chain) && (partial2 > chain2)) {
> +				ext4_free_branches(handle, inode, partial->bh,
> +						   partial->p + 1,
> +						   partial2->p,
> +						   (chain+n-1) - partial);
> +				BUFFER_TRACE(partial->bh, "call brelse");
> +				brelse(partial->bh);
> +				BUFFER_TRACE(partial2->bh, "call brelse");
> +				brelse(partial2->bh);
> +			}
> +			return 0;
>  		}
> -		i_data += num;
> -		if (level == 0) {
> -			num = 1;
> -			max = 1;
> +		/*
> +		 * Clear the ends of indirect blocks on the shared branch
> +		 * at the start of the range
> +		 */
> +		if (partial > chain) {
> +			ext4_free_branches(handle, inode, partial->bh,
> +				   partial->p + 1,
> +				   (__le32 *)partial->bh->b_data+addr_per_block,
> +				   (chain+n-1) - partial);
> +			BUFFER_TRACE(partial->bh, "call brelse");
> +			brelse(partial->bh);
> +			partial--;
> +		}
> +		/*
> +		 * Clear the ends of indirect blocks on the shared branch
> +		 * at the end of the range
> +		 */
> +		if (partial2 > chain2) {
> +			ext4_free_branches(handle, inode, partial2->bh,
> +					   (__le32 *)partial2->bh->b_data,
> +					   partial2->p,
> +					   (chain2+n-1) - partial2);
> +			BUFFER_TRACE(partial2->bh, "call brelse");
> +			brelse(partial2->bh);
> +			partial2--;
>  		}
>  	}
>  
> -err:
> -	return ret;
> +do_indirects:
> +	/* Kill the remaining (whole) subtrees */
> +	switch (offsets[0]) {
> +	default:
> +		if (++n >= n2)
> +			return 0;
> +		nr = i_data[EXT4_IND_BLOCK];
> +		if (nr) {
> +			ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 1);
> +			i_data[EXT4_IND_BLOCK] = 0;
> +		}
> +	case EXT4_IND_BLOCK:
> +		if (++n >= n2)
> +			return 0;
> +		nr = i_data[EXT4_DIND_BLOCK];
> +		if (nr) {
> +			ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 2);
> +			i_data[EXT4_DIND_BLOCK] = 0;
> +		}
> +	case EXT4_DIND_BLOCK:
> +		if (++n >= n2)
> +			return 0;
> +		nr = i_data[EXT4_TIND_BLOCK];
> +		if (nr) {
> +			ext4_free_branches(handle, inode, NULL, &nr, &nr+1, 3);
> +			i_data[EXT4_TIND_BLOCK] = 0;
> +		}
> +	case EXT4_TIND_BLOCK:
> +		;
> +	}
> +	return 0;
>  }
> -
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 7fcd68e..a5adc09 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3626,7 +3626,7 @@ int ext4_punch_hole(struct inode *inode, loff_t offset, loff_t length)
>  		ret = ext4_ext_remove_space(inode, first_block,
>  					    stop_block - 1);
>  	else
> -		ret = ext4_free_hole_blocks(handle, inode, first_block,
> +		ret = ext4_ind_remove_space(handle, inode, first_block,
>  					    stop_block);
>  
>  	up_write(&EXT4_I(inode)->i_data_sem);
> -- 
> 1.8.3.1
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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