linux-kernel - [PATCH] Btrfs: add another missing end_page_writeback on submit_extent

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Date:   Fri, 16 Dec 2016 15:41:50 +0900
From:   Takafumi Kubota <takafumi.kubota1012@...ab.ics.keio.ac.jp>
To:     linux-btrfs@...r.kernel.org
Cc:     clm@...com, jbacik@...com, dsterba@...e.com,
        linux-kernel@...r.kernel.org, fdmanana@...e.com, naota@...sp.net,
        Takafumi Kubota <takafumi.kubota1012@...ab.ics.keio.ac.jp>
Subject: [PATCH] Btrfs: add another missing end_page_writeback on submit_extent_page failure

This is actually inspired by Filipe's patch(55e3bd2e0c2e1).

When submit_extent_page() in __extent_writepage_io() fails,
Btrfs misses clearing a writeback bit of the failed page.
This causes the false under-writeback page.
Then, another sync task hangs in filemap_fdatawait_range(),
because it waits the false under-writeback page.

CPU0                            CPU1

__extent_writepage_io()
  ret = submit_extent_page() // fail

  if (ret)
    SetPageError(page)
    // miss clearing the writeback bit

                                sync()
                                  ...
                                  filemap_fdatawait_range()
                                    wait_on_page_writeback(page);
                                    // wait the false under-writeback page

Signed-off-by: Takafumi Kubota <takafumi.kubota1012@...ab.ics.keio.ac.jp>
---
 fs/btrfs/extent_io.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 1e67723..ef9793b 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3443,8 +3443,10 @@ static noinline_for_stack int __extent_writepage_io(struct inode *inode,
 					 bdev, &epd->bio, max_nr,
 					 end_bio_extent_writepage,
 					 0, 0, 0, false);
-		if (ret)
+		if (ret) {
 			SetPageError(page);
+			end_page_writeback(page);
+		}
 
 		cur = cur + iosize;
 		pg_offset += iosize;
-- 
1.9.3