[PATCH 3.13 143/163] nilfs2: fix data loss with mmap()

From: Kamal Mostafa
Date: Thu Oct 09 2014 - 17:44:48 EST -stable review patch. If anyone has any objections, please let me know.


From: Andreas Rohner <andreas.rohner@xxxxxxx>

commit 56d7acc792c0d98f38f22058671ee715ff197023 upstream.

This bug leads to reproducible silent data loss, despite the use of
msync(), sync() and a clean unmount of the file system. It is easily
reproducible with the following script:

----------------[BEGIN SCRIPT]--------------------
mkfs.nilfs2 -f /dev/sdb
mount /dev/sdb /mnt

dd if=/dev/zero bs=1M count=30 of=/mnt/testfile

umount /mnt
mount /dev/sdb /mnt
CHECKSUM_BEFORE="$(md5sum /mnt/testfile)"

/root/mmaptest/mmaptest /mnt/testfile 30 10 5

CHECKSUM_AFTER="$(md5sum /mnt/testfile)"
umount /mnt
mount /dev/sdb /mnt
CHECKSUM_AFTER_REMOUNT="$(md5sum /mnt/testfile)"
umount /mnt

----------------[END SCRIPT]--------------------

The mmaptest tool looks something like this (very simplified, with
error checking removed):

----------------[BEGIN mmaptest]--------------------
data = mmap(NULL, file_size - file_offset, PROT_READ | PROT_WRITE,
MAP_SHARED, fd, file_offset);

for (i = 0; i < write_count; ++i) {
memcpy(data + i * 4096, buf, sizeof(buf));
msync(data, file_size - file_offset, MS_SYNC))
----------------[END mmaptest]--------------------

The output of the script looks something like this:

BEFORE MMAP: 281ed1d5ae50e8419f9b978aab16de83 /mnt/testfile
AFTER MMAP: 6604a1c31f10780331a6850371b3a313 /mnt/testfile
AFTER REMOUNT: 281ed1d5ae50e8419f9b978aab16de83 /mnt/testfile

So it is clear, that the changes done using mmap() do not survive a
remount. This can be reproduced a 100% of the time. The problem was
introduced in commit 136e8770cd5d ("nilfs2: fix issue of
nilfs_set_page_dirty() for page at EOF boundary").

If the page was read with mpage_readpage() or mpage_readpages() for
example, then it has no buffers attached to it. In that case
page_has_buffers(page) in nilfs_set_page_dirty() will be false.
Therefore nilfs_set_file_dirty() is never called and the pages are never
collected and never written to disk.

This patch fixes the problem by also calling nilfs_set_file_dirty() if the
page has no buffers attached to it.

[akpm@xxxxxxxxxxxxxxxxxxxx: s/PAGE_SHIFT/PAGE_CACHE_SHIFT/]
Signed-off-by: Andreas Rohner <andreas.rohner@xxxxxxx>
Tested-by: Andreas Rohner <andreas.rohner@xxxxxxx>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Kamal Mostafa <kamal@xxxxxxxxxxxxx>
fs/nilfs2/inode.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 7e350c5..1e0bbae 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -24,6 +24,7 @@
#include <linux/buffer_head.h>
#include <linux/gfp.h>
#include <linux/mpage.h>
+#include <linux/pagemap.h>
#include <linux/writeback.h>
#include <linux/aio.h>
#include "nilfs.h"
@@ -219,10 +220,10 @@ static int nilfs_writepage(struct page *page, struct writeback_control *wbc)

static int nilfs_set_page_dirty(struct page *page)
+ struct inode *inode = page->mapping->host;
int ret = __set_page_dirty_nobuffers(page);

if (page_has_buffers(page)) {
- struct inode *inode = page->mapping->host;
unsigned nr_dirty = 0;
struct buffer_head *bh, *head;

@@ -245,6 +246,10 @@ static int nilfs_set_page_dirty(struct page *page)

if (nr_dirty)
nilfs_set_file_dirty(inode, nr_dirty);
+ } else if (ret) {
+ unsigned nr_dirty = 1 << (PAGE_CACHE_SHIFT - inode->i_blkbits);
+ nilfs_set_file_dirty(inode, nr_dirty);
return ret;

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