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

Jaegeuk Kim
2016-07-01T00:03:16Z

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