linux-ext4 - [PATCH] Revert "ext4: use ext4_write_inode() when fsyncing w/o a journal"

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Date:   Thu, 31 Jan 2019 23:42:19 -0500
From:   Theodore Ts'o <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
CC:     <jack@...e.cz>, Theodore Ts'o <tytso@....edu>
Subject: [PATCH] Revert "ext4: use ext4_write_inode() when fsyncing w/o a journal"

This reverts commit ad211f3e94b314a910d4af03178a0b52a7d1ee0a.

As Jan Kara pointed out, this change was unsafe since it means we lose
the call to sync_mapping_buffers() in the nojournal case.  The
original point of the commit was avoid taking the inode mutex (since
it causes a lockdep warning in generic/113); but we need the mutex in
order to call sync_mapping_buffers().

The real fix to this problem was discussed here:

https://lore.kernel.org/lkml/20181025150540.259281-4-bvanassche@acm.org

The proposed patch was to fix a syzbot complaint, but the problem can
also demonstrated via "kvm-xfstests -c nojournal generic/113".
Multiple solutions were discused in the e-mail thread, but none have
landed in the kernel as of this writing.  Anyway, commit
ad211f3e94b314 is absolutely the wrong way to suppress the lockdep, so
revert it.

Fixes: ad211f3e94b314a910d4af03178a0b52a7d1ee0a ("ext4: use ext4_write_inode() when fsyncing w/o a journal")
Signed-off-by: Theodore Ts'o <tytso@....edu>
Reported: Jan Kara <jack@...e.cz>
---
 fs/ext4/fsync.c | 13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/fs/ext4/fsync.c b/fs/ext4/fsync.c
index 712f00995390..5508baa11bb6 100644
--- a/fs/ext4/fsync.c
+++ b/fs/ext4/fsync.c
@@ -116,16 +116,8 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 		goto out;
 	}

-	ret = file_write_and_wait_range(file, start, end);
-	if (ret)
-		return ret;
-
 	if (!journal) {
-		struct writeback_control wbc = {
-			.sync_mode = WB_SYNC_ALL
-		};
-
-		ret = ext4_write_inode(inode, &wbc);
+		ret = __generic_file_fsync(file, start, end, datasync);
 		if (!ret)
 			ret = ext4_sync_parent(inode);
 		if (test_opt(inode->i_sb, BARRIER))
@@ -133,6 +125,9 @@ int ext4_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
 		goto out;
 	}

+	ret = file_write_and_wait_range(file, start, end);
+	if (ret)
+		return ret;
 	/*
 	 * data=writeback,ordered:
 	 *  The caller's filemap_fdatawrite()/wait will sync the data.
-- 
2.19.1