Patch "nilfs2: fix race condition that causes file system corruption" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    nilfs2: fix race condition that causes file system corruption

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     nilfs2-fix-race-condition-that-causes-file-system-corruption.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From 31ccb1f7ba3cfe29631587d451cf5bb8ab593550 Mon Sep 17 00:00:00 2001
From: Andreas Rohner <andreas.rohner@gmx.net>
Date: Fri, 17 Nov 2017 15:29:35 -0800
Subject: nilfs2: fix race condition that causes file system corruption

From: Andreas Rohner <andreas.rohner@gmx.net>

commit 31ccb1f7ba3cfe29631587d451cf5bb8ab593550 upstream.

There is a race condition between nilfs_dirty_inode() and
nilfs_set_file_dirty().

When a file is opened, nilfs_dirty_inode() is called to update the
access timestamp in the inode.  It calls __nilfs_mark_inode_dirty() in a
separate transaction.  __nilfs_mark_inode_dirty() caches the ifile
buffer_head in the i_bh field of the inode info structure and marks it
as dirty.

After some data was written to the file in another transaction, the
function nilfs_set_file_dirty() is called, which adds the inode to the
ns_dirty_files list.

Then the segment construction calls nilfs_segctor_collect_dirty_files(),
which goes through the ns_dirty_files list and checks the i_bh field.
If there is a cached buffer_head in i_bh it is not marked as dirty
again.

Since nilfs_dirty_inode() and nilfs_set_file_dirty() use separate
transactions, it is possible that a segment construction that writes out
the ifile occurs in-between the two.  If this happens the inode is not
on the ns_dirty_files list, but its ifile block is still marked as dirty
and written out.

In the next segment construction, the data for the file is written out
and nilfs_bmap_propagate() updates the b-tree.  Eventually the bmap root
is written into the i_bh block, which is not dirty, because it was
written out in another segment construction.

As a result the bmap update can be lost, which leads to file system
corruption.  Either the virtual block address points to an unallocated
DAT block, or the DAT entry will be reused for something different.

The error can remain undetected for a long time.  A typical error
message would be one of the "bad btree" errors or a warning that a DAT
entry could not be found.

This bug can be reproduced reliably by a simple benchmark that creates
and overwrites millions of 4k files.

Link: http://lkml.kernel.org/r/1509367935-3086-2-git-send-email-konishi.ryusuke@lab.ntt.co.jp
Signed-off-by: Andreas Rohner <andreas.rohner@gmx.net>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Tested-by: Andreas Rohner <andreas.rohner@gmx.net>
Tested-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 fs/nilfs2/segment.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1945,8 +1945,6 @@ static int nilfs_segctor_collect_dirty_f
 					      "failed to get inode block.\n");
 				return err;
 			}
-			mark_buffer_dirty(ibh);
-			nilfs_mdt_mark_dirty(ifile);
 			spin_lock(&nilfs->ns_inode_lock);
 			if (likely(!ii->i_bh))
 				ii->i_bh = ibh;
@@ -1955,6 +1953,10 @@ static int nilfs_segctor_collect_dirty_f
 			goto retry;
 		}
 
+		// Always redirty the buffer to avoid race condition
+		mark_buffer_dirty(ii->i_bh);
+		nilfs_mdt_mark_dirty(ifile);
+
 		clear_bit(NILFS_I_QUEUED, &ii->i_state);
 		set_bit(NILFS_I_BUSY, &ii->i_state);
 		list_move_tail(&ii->i_dirty, &sci->sc_dirty_files);


Patches currently in stable-queue which might be from andreas.rohner@gmx.net are

queue-4.4/nilfs2-fix-race-condition-that-causes-file-system-corruption.patch