[f2fs-dev] [PATCH] f2fs: compress: fix to wait page writeback in f2fs_write_raw_pages()

[f2fs-dev] [PATCH] f2fs: compress: fix to wait page writeback in f2fs_write_raw_pages()

[Yangtao Li via Linux-f2fs-devel]

From: liyangtao <11127627@bbktel.com>

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.

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: liyangtao <11127627@bbktel.com>
---
 fs/f2fs/compress.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/fs/f2fs/compress.c b/fs/f2fs/compress.c
index 93fec1d37899..904af359fa8e 100644
--- a/fs/f2fs/compress.c
+++ b/fs/f2fs/compress.c
@@ -1456,6 +1456,14 @@ 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)
+				f2fs_wait_on_page_writeback(cc->rpages[i],
+						DATA, true, true);
+			else
+				goto continue_unlock;
+		}
+
 		if (!clear_page_dirty_for_io(cc->rpages[i]))
 			goto continue_unlock;
 
-- 
2.35.1



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Re: [f2fs-dev] [PATCH] f2fs: compress: fix to wait page writeback in f2fs_write_raw_pages()

[Christoph Hellwig]

On Thu, Mar 16, 2023 at 05:36:32PM +0800, Yangtao Li wrote:
> +		if (PageWriteback(cc->rpages[i])) {
> +			if (wbc->sync_mode != WB_SYNC_NONE)
> +				f2fs_wait_on_page_writeback(cc->rpages[i],
> +						DATA, true, true);
> +			else
> +				goto continue_unlock;

Please avoid the else by doing the goto in the branch:

		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);


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