linux-kernel - Re: [PATCH V4] f2fs: Avoid double lock for cp

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Date:   Wed, 6 May 2020 14:21:38 +0800
From:   Chao Yu <yuchao0@...wei.com>
To:     Sayali Lokhande <sayalil@...eaurora.org>, <jaegeuk@...nel.org>,
        <linux-f2fs-devel@...ts.sourceforge.net>
CC:     <stummala@...eaurora.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V4] f2fs: Avoid double lock for cp_rwsem during checkpoint

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@...eaurora.org>

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

Thanks,