linux-ext4 - Re: [PATCH 03/10] ext4: fix unwritten counter leakage

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Date:	Wed, 26 Sep 2012 15:07:14 +0200
From:	Jan Kara <jack@...e.cz>
To:	Dmitry Monakhov <dmonakhov@...nvz.org>
Cc:	linux-ext4@...r.kernel.org, tytso@....edu, jack@...e.cz,
	lczerner@...hat.com
Subject: Re: [PATCH 03/10] ext4: fix unwritten counter leakage

On Mon 24-09-12 15:44:13, Dmitry Monakhov wrote:
> ext4_set_io_unwritten_flag() will increment i_unwritten counter, so
> once we mark end_io with END_IO_UNWRITTEN we have to revert it back
                           ^^ EXT4_IO_END_UNWRITTEN
> on error path.
> 
>  - add missed error checks to prevent counter leakage
>  - ext4_end_io_nolock() will clear END_IO_UNWRITTEN flag to signal
                                     ^^ EXT4_IO_END_UNWRITTEN
>    that conversion finished.
>  - add BUGON to free_end_io() to prevent similar leackage in future.
         ^^ BUG_ON    ^^ext4_free_io_end()         ^^ leakage

> Visiable effect of this bug is that unaligned aio_stress may deadlock
  ^^ Visible

  Umm, and won't it be more foolproof it we just decrement i_unwritten in
ext4_free_io_end() when we see EXT4_IO_END_UNWRITTEN set?

  That still leaves the mess with EXT4_STATE_DIO_UNWRITTEN unhandled. But
that's a separate issue. We seem to clear that flag only in
ext4_ext_direct_IO() although it could be set even when buffered write
converts extents. And error cases seem to be buggy as well.

								Honza

> Signed-off-by: Dmitry Monakhov <dmonakhov@...nvz.org>
> ---
>  fs/ext4/extents.c |   21 ++++++++++++++-------
>  fs/ext4/page-io.c |    6 +++++-
>  2 files changed, 19 insertions(+), 8 deletions(-)
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 6eb6b0c..739c21d 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3660,6 +3660,8 @@ ext4_ext_handle_uninitialized_extents(handle_t *handle, struct inode *inode,
>  	if ((flags & EXT4_GET_BLOCKS_PRE_IO)) {
>  		ret = ext4_split_unwritten_extents(handle, inode, map,
>  						   path, flags);
> +		if (ret <= 0)
> +			goto out;
>  		/*
>  		 * Flag the inode(non aio case) or end_io struct (aio case)
>  		 * that this IO needs to conversion to written when IO is
> @@ -3905,6 +3907,7 @@ int ext4_ext_map_blocks(handle_t *handle, struct inode *inode,
>  	struct ext4_allocation_request ar;
>  	ext4_io_end_t *io = (ext4_io_end_t*) EXT4_CUR_AIO_DIO(inode);
>  	ext4_lblk_t cluster_offset;
> +	int set_unwritten = 0;
>  
>  	ext_debug("blocks %u/%u requested for inode %lu\n",
>  		  map->m_lblk, map->m_len, inode->i_ino);
> @@ -4127,13 +4130,8 @@ got_allocated_blocks:
>  		 * For non asycn direct IO case, flag the inode state
>  		 * that we need to perform conversion when IO is done.
>  		 */
> -		if ((flags & EXT4_GET_BLOCKS_PRE_IO)) {
> -			if (io)
> -				ext4_set_io_unwritten_flag(inode, io);
> -			else
> -				ext4_set_inode_state(inode,
> -						     EXT4_STATE_DIO_UNWRITTEN);
> -		}
> +		if ((flags & EXT4_GET_BLOCKS_PRE_IO))
> +			set_unwritten = 1;
>  		if (ext4_should_dioread_nolock(inode))
>  			map->m_flags |= EXT4_MAP_UNINIT;
>  	}
> @@ -4145,6 +4143,15 @@ got_allocated_blocks:
>  	if (!err)
>  		err = ext4_ext_insert_extent(handle, inode, path,
>  					     &newex, flags);
> +
> +	if (!err && set_unwritten) {
> +		if (io)
> +			ext4_set_io_unwritten_flag(inode, io);
> +		else
> +			ext4_set_inode_state(inode,
> +					     EXT4_STATE_DIO_UNWRITTEN);
> +	}
> +
>  	if (err && free_on_err) {
>  		int fb_flags = flags & EXT4_GET_BLOCKS_DELALLOC_RESERVE ?
>  			EXT4_FREE_BLOCKS_NO_QUOT_UPDATE : 0;
> diff --git a/fs/ext4/page-io.c b/fs/ext4/page-io.c
> index de77e31..9970022 100644
> --- a/fs/ext4/page-io.c
> +++ b/fs/ext4/page-io.c
> @@ -71,6 +71,8 @@ void ext4_free_io_end(ext4_io_end_t *io)
>  	int i;
>  
>  	BUG_ON(!io);
> +	BUG_ON(io->flag & EXT4_IO_END_UNWRITTEN);
> +
>  	if (io->page)
>  		put_page(io->page);
>  	for (i = 0; i < io->num_io_pages; i++)
> @@ -94,6 +96,8 @@ int ext4_end_io_nolock(ext4_io_end_t *io)
>  	ssize_t size = io->size;
>  	int ret = 0;
>  
> +	BUG_ON(!(io->flag & EXT4_IO_END_UNWRITTEN));
> +
>  	ext4_debug("ext4_end_io_nolock: io 0x%p from inode %lu,list->next 0x%p,"
>  		   "list->prev 0x%p\n",
>  		   io, inode->i_ino, io->list.next, io->list.prev);
> @@ -106,7 +110,7 @@ int ext4_end_io_nolock(ext4_io_end_t *io)
>  			 "(inode %lu, offset %llu, size %zd, error %d)",
>  			 inode->i_ino, offset, size, ret);
>  	}
> -
> +	io->flag &= ~EXT4_IO_END_UNWRITTEN;
>  	if (io->iocb)
>  		aio_complete(io->iocb, io->result, 0);
>  
> -- 
> 1.7.7.6
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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