Andreas Rohner
2014-09-15 19:47:30 UTC
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
# create 30MB testfile
dd if=/dev/zero bs=1M count=30 of=/mnt/testfile
umount /mnt
mount /dev/sdb /mnt
CHECKSUM_BEFORE="$(md5sum /mnt/testfile)"
# simple tool that opens /mnt/testfile and
# writes a few blocks using mmap at a 5MB offset
/root/mmaptest/mmaptest /mnt/testfile 30 10 5
sync
CHECKSUM_AFTER="$(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 the following commit:
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 <andreas.rohner-***@public.gmane.org>
---
fs/nilfs2/inode.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 6252b17..9e3c525 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -219,10 +219,10 @@ 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 +245,10 @@ 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_SHIFT - inode->i_blkbits);
+
+ nilfs_set_file_dirty(inode, nr_dirty);
}
return ret;
}
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
# create 30MB testfile
dd if=/dev/zero bs=1M count=30 of=/mnt/testfile
umount /mnt
mount /dev/sdb /mnt
CHECKSUM_BEFORE="$(md5sum /mnt/testfile)"
# simple tool that opens /mnt/testfile and
# writes a few blocks using mmap at a 5MB offset
/root/mmaptest/mmaptest /mnt/testfile 30 10 5
sync
CHECKSUM_AFTER="$(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 the following commit:
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 <andreas.rohner-***@public.gmane.org>
---
fs/nilfs2/inode.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/fs/nilfs2/inode.c b/fs/nilfs2/inode.c
index 6252b17..9e3c525 100644
--- a/fs/nilfs2/inode.c
+++ b/fs/nilfs2/inode.c
@@ -219,10 +219,10 @@ 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 +245,10 @@ 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_SHIFT - inode->i_blkbits);
+
+ nilfs_set_file_dirty(inode, nr_dirty);
}
return ret;
}
--
2.1.0
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