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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
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.. | ||
alloc.c | ||
alloc.h | ||
bmap.c | ||
bmap.h | ||
btnode.c | ||
btnode.h | ||
btree.c | ||
btree.h | ||
cpfile.c | ||
cpfile.h | ||
dat.c | ||
dat.h | ||
dir.c | ||
direct.c | ||
direct.h | ||
export.h | ||
file.c | ||
gcinode.c | ||
ifile.c | ||
ifile.h | ||
inode.c | ||
ioctl.c | ||
Kconfig | ||
Makefile | ||
mdt.c | ||
mdt.h | ||
namei.c | ||
nilfs.h | ||
page.c | ||
page.h | ||
recovery.c | ||
segbuf.c | ||
segbuf.h | ||
segment.c | ||
segment.h | ||
sufile.c | ||
sufile.h | ||
super.c | ||
sysfs.c | ||
sysfs.h | ||
the_nilfs.c | ||
the_nilfs.h |