From:   Xin Yin <yinxin.x@bytedance.com>
To:     harshadshirwadkar@gmail.com, tytso@mit.edu,
        adilger.kernel@dilger.ca
Cc:     linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org,
        Xin Yin <yinxin.x@bytedance.com>
Subject: [PATCH] ext4: call fallocate may cause process to hang when using fast commit
Date:   Thu, 16 Dec 2021 16:03:03 +0800
Message-Id: <20211216080303.388139-1-yinxin.x@bytedance.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

If open a file with O_SYNC, and call fallocate with mode=0.when using
fast commit, will cause the process to hang.

During the fast_commit procedure, it will wait for inode update done.
call ext4_fc_stop_update() before ext4_fc_commit() to mark inode
complete update.

Signed-off-by: Xin Yin <yinxin.x@bytedance.com>
---
 fs/ext4/extents.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
index 4108896d471b..92db33887b6c 100644
--- a/fs/ext4/extents.c
+++ b/fs/ext4/extents.c
@@ -4707,8 +4707,12 @@ long ext4_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
 		goto out;
 
 	if (file->f_flags & O_SYNC && EXT4_SB(inode->i_sb)->s_journal) {
+		ext4_fc_stop_update(inode);
 		ret = ext4_fc_commit(EXT4_SB(inode->i_sb)->s_journal,
 					EXT4_I(inode)->i_sync_tid);
+		inode_unlock(inode);
+		trace_ext4_fallocate_exit(inode, offset, max_blocks, ret);
+		return ret;
 	}
 out:
 	inode_unlock(inode);
-- 
2.20.1