Re: [f2fs-dev] [PATCH v2] f2fs: fix to writeout dirty inode during node flush

[Eric Biggers]

On Thu, Aug 22, 2019 at 08:17:56PM +0800, Chao Yu wrote:
> As Eric reported:
> 
> On xfstest generic/204 on f2fs, I'm getting a kernel BUG.
> 
>  allocate_segment_by_default+0x9d/0x100 [f2fs]
>  f2fs_allocate_data_block+0x3c0/0x5c0 [f2fs]
>  do_write_page+0x62/0x110 [f2fs]
>  f2fs_do_write_node_page+0x2b/0xa0 [f2fs]
>  __write_node_page+0x2ec/0x590 [f2fs]
>  f2fs_sync_node_pages+0x756/0x7e0 [f2fs]
>  block_operations+0x25b/0x350 [f2fs]
>  f2fs_write_checkpoint+0x104/0x1150 [f2fs]
>  f2fs_sync_fs+0xa2/0x120 [f2fs]
>  f2fs_balance_fs_bg+0x33c/0x390 [f2fs]
>  f2fs_write_node_pages+0x4c/0x1f0 [f2fs]
>  do_writepages+0x1c/0x70
>  __writeback_single_inode+0x45/0x320
>  writeback_sb_inodes+0x273/0x5c0
>  wb_writeback+0xff/0x2e0
>  wb_workfn+0xa1/0x370
>  process_one_work+0x138/0x350
>  worker_thread+0x4d/0x3d0
>  kthread+0x109/0x140
> 
> The root cause of this issue is, in a very small partition, e.g.
> in generic/204 testcase of fstest suit, filesystem's free space
> is 50MB, so at most we can write 12800 inline inode with command:
> `echo XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX > $SCRATCH_MNT/$i`,
> then filesystem will have:
> - 12800 dirty inline data page
> - 12800 dirty inode page
> - and 12800 dirty imeta (dirty inode)
> 
> When we flush node-inode's page cache, we can also flush inline
> data with each inode page, however it will run out-of-free-space
> in device, then once it triggers checkpoint, there is no room for
> huge number of imeta, at this time, GC is useless, as there is no
> dirty segment at all.
> 
> In order to fix this, we try to recognize inode page during
> node_inode's page flushing, and update inode page from dirty inode,
> so that later another imeta (dirty inode) flush can be avoided.
> 
> Reported-by: Eric Biggers <ebiggers@xxxxxxxxxx>
> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> ---
> v2: fix potential deadlock
>  fs/f2fs/node.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index d9ba1db2d01e..e5044eec8097 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -1762,6 +1762,47 @@ int f2fs_fsync_node_pages(struct f2fs_sb_info *sbi, struct inode *inode,
>  	return ret ? -EIO: 0;
>  }
>  
> +static int f2fs_match_ino(struct inode *inode, unsigned long ino, void *data)
> +{
> +	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
> +	bool clean;
> +
> +	if (inode->i_ino != ino)
> +		return 0;
> +
> +	if (!is_inode_flag_set(inode, FI_DIRTY_INODE))
> +		return 0;
> +
> +	spin_lock(&sbi->inode_lock[DIRTY_META]);
> +	clean = list_empty(&F2FS_I(inode)->gdirty_list);
> +	spin_unlock(&sbi->inode_lock[DIRTY_META]);
> +
> +	if (clean)
> +		return 0;
> +
> +	inode = igrab(inode);
> +	if (!inode)
> +		return 0;
> +	return 1;
> +}
> +
> +static bool flush_dirty_inode(struct page *page)
> +{
> +	struct f2fs_sb_info *sbi = F2FS_P_SB(page);
> +	struct inode *inode;
> +	nid_t ino = ino_of_node(page);
> +
> +	inode = find_inode_nowait(sbi->sb, ino, f2fs_match_ino, NULL);
> +	if (!inode)
> +		return false;
> +
> +	f2fs_update_inode(inode, page);
> +	unlock_page(page);
> +
> +	iput(inode);
> +	return true;
> +}
> +
>  int f2fs_sync_node_pages(struct f2fs_sb_info *sbi,
>  				struct writeback_control *wbc,
>  				bool do_balance, enum iostat_type io_type)
> @@ -1785,6 +1826,7 @@ int f2fs_sync_node_pages(struct f2fs_sb_info *sbi,
>  		for (i = 0; i < nr_pages; i++) {
>  			struct page *page = pvec.pages[i];
>  			bool submitted = false;
> +			bool may_dirty = true;
>  
>  			/* give a priority to WB_SYNC threads */
>  			if (atomic_read(&sbi->wb_sync_req[NODE]) &&
> @@ -1832,6 +1874,13 @@ int f2fs_sync_node_pages(struct f2fs_sb_info *sbi,
>  				goto lock_node;
>  			}
>  
> +			/* flush dirty inode */
> +			if (IS_INODE(page) && may_dirty) {
> +				may_dirty = false;
> +				if (flush_dirty_inode(page))
> +					goto lock_node;
> +			}
> +
>  			f2fs_wait_on_page_writeback(page, NODE, true, true);
>  
>  			if (!clear_page_dirty_for_io(page))
> -- 
> 2.18.0.rc1
> 

Thanks, the test passes for me with this patch applied.

Tested-by: Eric Biggers <ebiggers@xxxxxxxxxx>