[f2fs-dev] [PATCH v2] f2fs: compress: fix to call f2fs_wait_on_page_writeback() in f2fs_write_raw_pages()

[f2fs-dev] [PATCH v2] f2fs: compress: fix to call f2fs_wait_on_page_writeback() in f2fs_write_raw_pages()

[Yangtao Li via Linux-f2fs-devel]

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@lst.de>
Fixes: 4c8ff7095bef ("f2fs: support data compression")
Fixes: 7377e853967b ("f2fs: compress: fix potential deadlock of compress file")
Signed-off-by: Qi Han <hanqi@vivo.com>
Signed-off-by: Yangtao Li <frank.li@vivo.com>
---
v2:
-avoid the else
 fs/f2fs/compress.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 93fec1d37899..9b7149534a58 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1456,6 +1456,12 @@ static int f2fs_write_raw_pages(struct compress_ctx *cc,
 		if (!PageDirty(cc->rpages[i]))
 			goto continue_unlock;
 
+		if (PageWriteback(cc->rpages[i])) {
+			if (wbc->sync_mode == WB_SYNC_NONE)
+				goto continue_unlock;
+			f2fs_wait_on_page_writeback(cc->rpages[i], DATA, true, true);
+		}
+
 		if (!clear_page_dirty_for_io(cc->rpages[i]))
 			goto continue_unlock;
 
-- 
2.35.1



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Re: [f2fs-dev] [PATCH v2] f2fs: compress: fix to call f2fs_wait_on_page_writeback() in f2fs_write_raw_pages()

[Chao Yu]

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@lst.de>
> Fixes: 4c8ff7095bef ("f2fs: support data compression")
> Fixes: 7377e853967b ("f2fs: compress: fix potential deadlock of compress file")
> Signed-off-by: Qi Han <hanqi@vivo.com>
> Signed-off-by: Yangtao Li <frank.li@vivo.com>

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

Thanks,


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Re: [f2fs-dev] [PATCH v2] f2fs: compress: fix to call f2fs_wait_on_page_writeback() in f2fs_write_raw_pages()

[patchwork-bot+f2fs]

Hello:

This patch was applied to jaegeuk/f2fs.git (dev)
by Jaegeuk Kim <jaegeuk@kernel.org>:

On Tue, 21 Mar 2023 01:22:18 +0800 you 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 }
> 
> [...]

Here is the summary with links:
  - [f2fs-dev,v2] f2fs: compress: fix to call f2fs_wait_on_page_writeback() in f2fs_write_raw_pages()
    https://git.kernel.org/jaegeuk/f2fs/c/08a8457cfd78

You are awesome, thank you!
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