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 in commit 136e8770cd
("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@linux-foundation.org: s/PAGE_SHIFT/PAGE_CACHE_SHIFT/]
Signed-off-by: Andreas Rohner <andreas.rohner@gmx.net>
Tested-by: Andreas Rohner <andreas.rohner@gmx.net>
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
parent
f13a568e5a
commit
56d7acc792
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@ -24,6 +24,7 @@
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#include <linux/buffer_head.h>
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#include <linux/gfp.h>
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#include <linux/mpage.h>
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#include <linux/pagemap.h>
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#include <linux/writeback.h>
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#include <linux/aio.h>
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#include "nilfs.h"
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@ -219,10 +220,10 @@ static int nilfs_writepage(struct page *page, struct writeback_control *wbc)
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static int nilfs_set_page_dirty(struct page *page)
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{
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struct inode *inode = page->mapping->host;
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int ret = __set_page_dirty_nobuffers(page);
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if (page_has_buffers(page)) {
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struct inode *inode = page->mapping->host;
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unsigned nr_dirty = 0;
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struct buffer_head *bh, *head;
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@ -244,6 +245,10 @@ static int nilfs_set_page_dirty(struct page *page)
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} while (bh = bh->b_this_page, bh != head);
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if (nr_dirty)
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nilfs_set_file_dirty(inode, nr_dirty);
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} else if (ret) {
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unsigned nr_dirty = 1 << (PAGE_CACHE_SHIFT - inode->i_blkbits);
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nilfs_set_file_dirty(inode, nr_dirty);
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}
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return ret;
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