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Subject: Re: [f2fs-dev] [PATCH] f2fs: fix livelock in swapfile writes
To:     Jaegeuk Kim <jaegeuk@kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-f2fs-devel@lists.sourceforge.net>
References: <20190731204353.62056-1-jaegeuk@kernel.org>
From:   Chao Yu <yuchao0@huawei.com>
Message-ID: <f500dafa-19f4-78ff-2645-2239fbf43eab@huawei.com>
Date:   Thu, 1 Aug 2019 09:53:08 +0800
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On 2019/8/1 4:43, Jaegeuk Kim wrote:
> This patch fixes livelock in the below call path when writing swap pages.
> 
> [46374.617256] c2    701  __switch_to+0xe4/0x100
> [46374.617265] c2    701  __schedule+0x80c/0xbc4
> [46374.617273] c2    701  schedule+0x74/0x98
> [46374.617281] c2    701  rwsem_down_read_failed+0x190/0x234
> [46374.617291] c2    701  down_read+0x58/0x5c
> [46374.617300] c2    701  f2fs_map_blocks+0x138/0x9a8
> [46374.617310] c2    701  get_data_block_dio_write+0x74/0x104
> [46374.617320] c2    701  __blockdev_direct_IO+0x1350/0x3930
> [46374.617331] c2    701  f2fs_direct_IO+0x55c/0x8bc
> [46374.617341] c2    701  __swap_writepage+0x1d0/0x3e8
> [46374.617351] c2    701  swap_writepage+0x44/0x54
> [46374.617360] c2    701  shrink_page_list+0x140/0xe80
> [46374.617371] c2    701  shrink_inactive_list+0x510/0x918
> [46374.617381] c2    701  shrink_node_memcg+0x2d4/0x804
> [46374.617391] c2    701  shrink_node+0x10c/0x2f8
> [46374.617400] c2    701  do_try_to_free_pages+0x178/0x38c
> [46374.617410] c2    701  try_to_free_pages+0x348/0x4b8
> [46374.617419] c2    701  __alloc_pages_nodemask+0x7f8/0x1014
> [46374.617429] c2    701  pagecache_get_page+0x184/0x2cc
> [46374.617438] c2    701  f2fs_new_node_page+0x60/0x41c
> [46374.617449] c2    701  f2fs_new_inode_page+0x50/0x7c
> [46374.617460] c2    701  f2fs_init_inode_metadata+0x128/0x530
> [46374.617472] c2    701  f2fs_add_inline_entry+0x138/0xd64
> [46374.617480] c2    701  f2fs_do_add_link+0xf4/0x178
> [46374.617488] c2    701  f2fs_create+0x1e4/0x3ac
> [46374.617497] c2    701  path_openat+0xdc0/0x1308
> [46374.617507] c2    701  do_filp_open+0x78/0x124
> [46374.617516] c2    701  do_sys_open+0x134/0x248
> [46374.617525] c2    701  SyS_openat+0x14/0x20
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> ---
>  fs/f2fs/data.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> index abbf14e9bd72..f49f243fd54f 100644
> --- a/fs/f2fs/data.c
> +++ b/fs/f2fs/data.c
> @@ -1372,7 +1372,7 @@ static int get_data_block_dio_write(struct inode *inode, sector_t iblock,
>  	return __get_data_block(inode, iblock, bh_result, create,
>  				F2FS_GET_BLOCK_DIO, NULL,
>  				f2fs_rw_hint_to_seg_type(inode->i_write_hint),
> -				true);
> +				IS_SWAPFILE(inode) ? false : true);

I suspect that we should use node_change for swapfile rather than just changing
may_write field to skip lock.

__do_map_lock()
if (flag == F2FS_GET_BLOCK_PRE_AIO || IS_SWAPFILE(inode)) {
	...
} else {
	...
}

Thanks,


>  }
>  
>  static int get_data_block_dio(struct inode *inode, sector_t iblock,
>