The patch titled
Subject: nilfs2: fix race condition that causes file system corruption
has been added to the -mm tree. Its filename is
nilfs2-fix-race-condition-that-causes-file-system-corruption.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/nilfs2-fix-race-condition-that-causes-file-system-corruption.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/nilfs2-fix-race-condition-that-causes-file-system-corruption.patch
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From: Andreas Rohner <andreas.rohner@xxxxxxx>
Subject: nilfs2: fix race condition that causes file system corruption
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@xxxxxxxxxxxxx
Signed-off-by: Andreas Rohner <andreas.rohner@xxxxxxx>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>
Tested-by: Andreas Rohner <andreas.rohner@xxxxxxx>
Tested-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/nilfs2/segment.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN fs/nilfs2/segment.c~nilfs2-fix-race-condition-that-causes-file-system-corruption fs/nilfs2/segment.c
--- a/fs/nilfs2/segment.c~nilfs2-fix-race-condition-that-causes-file-system-corruption
+++ a/fs/nilfs2/segment.c
@@ -1954,8 +1954,6 @@ static int nilfs_segctor_collect_dirty_f
err, ii->vfs_inode.i_ino);
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;
@@ -1964,6 +1962,10 @@ 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 -mm which might be from andreas.rohner@xxxxxxx are
nilfs2-fix-race-condition-that-causes-file-system-corruption.patch