Re: [PATCH 2/2] f2fs: fix to avoid data update racing between GC and DIO

[Jaegeuk Kim <jaegeuk@kernel.org>]

Hi Chao,

On Thu, Jun 30, 2016 at 04:42:48PM +0800, Chao Yu wrote:
> Datas in file can be operated by GC and DIO simultaneously, so we will
> face race case as below:
> 
> For write case:
> Thread A				Thread B
> - generic_file_direct_write
>  - invalidate_inode_pages2_range
>  - f2fs_direct_IO
>   - do_blockdev_direct_IO
>    - do_direct_IO
>     - get_more_blocks
> 					- f2fs_gc
> 					 - do_garbage_collect
> 					  - gc_data_segment
> 					   - move_data_page
> 					    - do_write_data_page
> 					    migrate data block to new block address
>    - dio_bio_submit
>    update user data to old block address
> 
> For read case:
> Thread A                                Thread B
> - generic_file_direct_write
>  - invalidate_inode_pages2_range
>  - f2fs_direct_IO
>   - do_blockdev_direct_IO
>    - do_direct_IO
>     - get_more_blocks
> 					- f2fs_balance_fs
> 					 - f2fs_gc
> 					  - do_garbage_collect
> 					   - gc_data_segment
> 					    - move_data_page
> 					     - do_write_data_page
> 					     migrate data block to new block address
> 					  - write_checkpoint
> 					   - do_checkpoint
> 					    - clear_prefree_segments
> 					     - f2fs_issue_discard
>                                              discard old block adress
>    - dio_bio_submit
>    update user buffer from obsolete block address
> 
> In order to fix this, for one file, we should let DIO and GC getting exclusion
> against with each other.
> 
> Signed-off-by: Chao Yu <yuchao0@huawei.com>
> ---
>  fs/f2fs/data.c  |  2 ++
>  fs/f2fs/f2fs.h  |  1 +
>  fs/f2fs/gc.c    | 14 +++++++++++++-
>  fs/f2fs/super.c |  1 +
>  4 files changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index ba4963f..08dc060 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1716,7 +1716,9 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
>  
>  	trace_f2fs_direct_IO_enter(inode, offset, count, iov_iter_rw(iter));
>  
> +	mutex_lock(&F2FS_I(inode)->dio_mutex);
>  	err = blockdev_direct_IO(iocb, inode, iter, get_data_block_dio);
> +	mutex_unlock(&F2FS_I(inode)->dio_mutex);

This means we need to sacrifice entire parallism even in the normal cases?
Can we find another way?

Thanks,

>  	if (iov_iter_rw(iter) == WRITE) {
>  		if (err > 0)
>  			set_inode_flag(inode, FI_UPDATE_WRITE);
> diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> index bd82b6d..a241576 100644
> --- a/fs/f2fs/f2fs.h
> +++ b/fs/f2fs/f2fs.h
> @@ -474,6 +474,7 @@ struct f2fs_inode_info {
>  	struct list_head inmem_pages;	/* inmemory pages managed by f2fs */
>  	struct mutex inmem_lock;	/* lock for inmemory pages */
>  	struct extent_tree *extent_tree;	/* cached extent_tree entry */
> +	struct mutex dio_mutex;		/* avoid racing between dio and gc */
>  };
>  
>  static inline void get_extent_info(struct extent_info *ext,
> diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
> index c2c4ac3..98e3763 100644
> --- a/fs/f2fs/gc.c
> +++ b/fs/f2fs/gc.c
> @@ -744,12 +744,24 @@ next_step:
>  		/* phase 3 */
>  		inode = find_gc_inode(gc_list, dni.ino);
>  		if (inode) {
> +			bool locked = false;
> +
> +			if (S_ISREG(inode->i_mode)) {
> +				if (!mutex_trylock(&F2FS_I(inode)->dio_mutex))
> +					continue;
> +				locked = true;
> +			}
> +
>  			start_bidx = start_bidx_of_node(nofs, inode)
>  								+ ofs_in_node;
> -			if (f2fs_encrypted_inode(inode) && S_ISREG(inode->i_mode))
> +			if (f2fs_encrypted_inode(inode) &&
> +							S_ISREG(inode->i_mode))
>  				move_encrypted_block(inode, start_bidx);
>  			else
>  				move_data_page(inode, start_bidx, gc_type);
> +			if (locked)
> +				mutex_unlock(&F2FS_I(inode)->dio_mutex);
> +
>  			stat_inc_data_blk_count(sbi, 1, gc_type);
>  		}
>  	}
> diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
> index 8c698e1..24aab3f 100644
> --- a/fs/f2fs/super.c
> +++ b/fs/f2fs/super.c
> @@ -575,6 +575,7 @@ static struct inode *f2fs_alloc_inode(struct super_block *sb)
>  	INIT_LIST_HEAD(&fi->gdirty_list);
>  	INIT_LIST_HEAD(&fi->inmem_pages);
>  	mutex_init(&fi->inmem_lock);
> +	mutex_init(&fi->dio_mutex);
>  
>  	/* Will be used by directory only */
>  	fi->i_dir_level = F2FS_SB(sb)->dir_level;
> -- 
> 2.8.2.311.gee88674

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