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From:   Daeho Jeong <daeho43@gmail.com>
To:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com
Cc:     Daeho Jeong <daehojeong@google.com>
Subject: [PATCH] f2fs: protect new segment allocation in expand_inode_data
Date:   Wed, 27 May 2020 13:02:31 +0900
Message-Id: <20200527040231.70891-1-daeho43@gmail.com>
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From: Daeho Jeong <daehojeong@google.com>

Found a new segemnt allocation without f2fs_lock_op() in
expand_inode_data(). So, when we do fallocate() for a pinned file
and trigger checkpoint very frequently and simultaneously. F2FS gets
stuck in the below code of do_checkpoint() forever.

  f2fs_sync_meta_pages(sbi, META, LONG_MAX, FS_CP_META_IO);
  /* Wait for all dirty meta pages to be submitted for IO */
                                                <= if fallocate() here,
  f2fs_wait_on_all_pages(sbi, F2FS_DIRTY_META); <= it'll wait forever.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
---
 fs/f2fs/file.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index f7de2a1da528..14ace885baa9 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1660,7 +1660,11 @@ static int expand_inode_data(struct inode *inode, loff_t offset,
 
 		down_write(&sbi->pin_sem);
 		map.m_seg_type = CURSEG_COLD_DATA_PINNED;
+
+		f2fs_lock_op(sbi);
 		f2fs_allocate_new_segments(sbi, CURSEG_COLD_DATA);
+		f2fs_unlock_op(sbi);
+
 		err = f2fs_map_blocks(inode, &map, 1, F2FS_GET_BLOCK_PRE_DIO);
 		up_write(&sbi->pin_sem);
 
-- 
2.27.0.rc0.183.gde8f92d652-goog