[3.13.y.z extended stable] Patch "nilfs2: fix data loss with mmap()" has been added to staging queue

[Kamal Mostafa]

This is a note to let you know that I have just added a patch titled

    nilfs2: fix data loss with mmap()

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.9.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 65f419059f464006a417edecedd5d49cdd5c74b8 Mon Sep 17 00:00:00 2001
From: Andreas Rohner <andreas.rohner at gmx.net>
Date: Thu, 25 Sep 2014 16:05:14 -0700
Subject: nilfs2: fix data loss with mmap()

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

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

  echo "BEFORE MMAP:\t$CHECKSUM_BEFORE"
  echo "AFTER MMAP:\t$CHECKSUM_AFTER"
  echo "AFTER REMOUNT:\t$CHECKSUM_AFTER_REMOUNT"
  ----------------[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 at linux-foundation.org: s/PAGE_SHIFT/PAGE_CACHE_SHIFT/]
Signed-off-by: Andreas Rohner <andreas.rohner at gmx.net>
Tested-by: Andreas Rohner <andreas.rohner at gmx.net>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke at lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 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;
 }
--
1.9.1