linux-kernel - Re: [PATCH v2] f2fs: compress: fix to call f2fs_wait_on_page_writeback() in f2fs_write_raw

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Message-ID: <67aaa031-ab25-ffe4-ea56-3f3e4c0ac3d1@kernel.org>
Date:   Sun, 26 Mar 2023 21:47:42 +0800
From:   Chao Yu <chao@...nel.org>
To:     Yangtao Li <frank.li@...o.com>, jaegeuk@...nel.org
Cc:     linux-f2fs-devel@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org, hanqi@...o.com,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2] f2fs: compress: fix to call
 f2fs_wait_on_page_writeback() in f2fs_write_raw_pages()

On 2023/3/21 1:22, Yangtao Li wrote:
> BUG_ON() will be triggered when writing files concurrently,
> because the same page is writtenback multiple times.
> 
> 1597 void folio_end_writeback(struct folio *folio)
> 1598 {
> 		......
> 1618     if (!__folio_end_writeback(folio))
> 1619         BUG();
> 		......
> 1625 }
> 
> kernel BUG at mm/filemap.c:1619!
> Call Trace:
>   <TASK>
>   f2fs_write_end_io+0x1a0/0x370
>   blk_update_request+0x6c/0x410
>   blk_mq_end_request+0x15/0x130
>   blk_complete_reqs+0x3c/0x50
>   __do_softirq+0xb8/0x29b
>   ? sort_range+0x20/0x20
>   run_ksoftirqd+0x19/0x20
>   smpboot_thread_fn+0x10b/0x1d0
>   kthread+0xde/0x110
>   ? kthread_complete_and_exit+0x20/0x20
>   ret_from_fork+0x22/0x30
>   </TASK>
> 
> Below is the concurrency scenario:
> 
> [Process A]		[Process B]		[Process C]
> f2fs_write_raw_pages()
>    - redirty_page_for_writepage()
>    - unlock page()
> 			f2fs_do_write_data_page()
> 			  - lock_page()
> 			  - clear_page_dirty_for_io()
> 			  - set_page_writeback() [1st writeback]
> 			    .....
> 			    - unlock page()
> 
> 						generic_perform_write()
> 						  - f2fs_write_begin()
> 						    - wait_for_stable_page()
> 
> 						  - f2fs_write_end()
> 						    - set_page_dirty()
> 
>    - lock_page()
>      - f2fs_do_write_data_page()
>        - set_page_writeback() [2st writeback]
> 
> This problem was introduced by the previous commit 7377e853967b ("f2fs:
> compress: fix potential deadlock of compress file"). All pagelocks were
> released in f2fs_write_raw_pages(), but whether the page was
> in the writeback state was ignored in the subsequent writing process.
> Let's fix it by waiting for the page to writeback before writing.
> 
> Cc: Christoph Hellwig <hch@....de>
> Fixes: 4c8ff7095bef ("f2fs: support data compression")
> Fixes: 7377e853967b ("f2fs: compress: fix potential deadlock of compress file")
> Signed-off-by: Qi Han <hanqi@...o.com>
> Signed-off-by: Yangtao Li <frank.li@...o.com>

Reviewed-by: Chao Yu <chao@...nel.org>

Thanks,