Re: [PATCH V4] f2fs: Avoid double lock for cp_rwsem during checkpoint

Chao Yu
2020-05-06T06:21:46Z

On 2020/4/30 18:58, Sayali Lokhande wrote:
> There could be a scenario where f2fs_sync_node_pages gets
> called during checkpoint, which in turn tries to flush
> inline data and calls iput(). This results in deadlock as
> iput() tries to hold cp_rwsem, which is already held at the
> beginning by checkpoint->block_operations().
>
> Call stack :
>
> Thread A Thread B
> f2fs_write_checkpoint()
> - block_operations(sbi)
> - f2fs_lock_all(sbi);
> - down_write(&sbi->cp_rwsem);
>
> - open()
> - igrab()
> - write() write inline data
> - unlink()
> - f2fs_sync_node_pages()
> - if (is_inline_node(page))
> - flush_inline_data()
> - ilookup()
> page = f2fs_pagecache_get_page()
> if (!page)
> goto iput_out;
> iput_out:
> -close()
> -iput()
> iput(inode);
> - f2fs_evict_inode()
> - f2fs_truncate_blocks()
> - f2fs_lock_op()
> - down_read(&sbi->cp_rwsem);
>
> Fixes: 2049d4fcb057 ("f2fs: avoid multiple node page writes due to inline_data")
> Signed-off-by: Sayali Lokhande <sayalil@codeaurora.org>

Reviewed-by: Chao Yu <yuchao0@huawei.com>

Thanks,