The patch titled
Subject: nilfs2: fix data loss with mmap()
has been added to the -mm tree. Its filename is
nilfs2-fix-data-loss-with-mmap.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/nilfs2-fix-data-loss-with-mmap.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/nilfs2-fix-data-loss-with-mmap.patch
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------------------------------------------------------
From: Andreas Rohner <[email protected]>
Subject: nilfs2: fix data loss with mmap()
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 with 136e877 ("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.
Signed-off-by: Andreas Rohner <[email protected]>
Tested-by: Andreas Rohner <[email protected]>
Signed-off-by: Ryusuke Konishi <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---
fs/nilfs2/inode.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff -puN fs/nilfs2/inode.c~nilfs2-fix-data-loss-with-mmap fs/nilfs2/inode.c
--- a/fs/nilfs2/inode.c~nilfs2-fix-data-loss-with-mmap
+++ a/fs/nilfs2/inode.c
@@ -219,10 +219,10 @@ static int nilfs_writepage(struct page *
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 +245,10 @@ static int nilfs_set_page_dirty(struct p
if (nr_dirty)
nilfs_set_file_dirty(inode, nr_dirty);
+ } else if (ret) {
+ unsigned nr_dirty = 1 << (PAGE_SHIFT - inode->i_blkbits);
+
+ nilfs_set_file_dirty(inode, nr_dirty);
}
return ret;
}
_
Patches currently in -mm which might be from [email protected] are
nilfs2-fix-data-loss-with-mmap.patch
nilfs2-fix-data-loss-with-mmap-fix.patch
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