From: Yongpeng Yang <[email protected]>
Neither F2FS nor VFS invalidates the block device page cache, which
results in reading stale metadata. An example scenario is shown below:
Terminal A Terminal B
mount /dev/vdb /mnt/f2fs
touch mx // ino = 4
sync
dump.f2fs -i 4 /dev/vdb// block on "[Y/N]"
touch mx2 // ino = 5
sync
umount /mnt/f2fs
dump.f2fs -i 5 /dev/vdb // block addr is 0
After umount, the block device page cache is not purged, causing
`dump.f2fs -i 5 /dev/vdb` to read stale metadata and see inode 5 with
block address 0.
Btrfs has encountered a similar issue before, the solution there was to
call sync_blockdev() and invalidate_bdev() when the device is closed:
mail-archive.com/[email protected]/msg54188.html
For the root user, the f2fs kernel calls sync_blockdev() on umount to
flush all cached data to disk, and f2fs-tools can release the page cache
by issuing ioctl(fd, BLKFLSBUF) when accessing the device. However,
non-root users are not permitted to drop the page cache, and may still
observe stale data.
This patch calls sync_blockdev() and invalidate_bdev() during umount to
invalidate the block device page cache, thereby preventing stale
metadata from being read.
Note that this may result in an extra sync_blockdev() call on the first
device, in both f2fs_put_super() and kill_block_super(). The second call
do nothing, as there are no dirty pages left to flush. It ensures that
non-root users do not observe stale data.
Signed-off-by: Yongpeng Yang <[email protected]>
---
v2:
- Add commit message explaining why sync_blockdev is called redundantly
for the first device.
---
fs/f2fs/super.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index 40079fd7886b..b624ed253a95 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -2088,6 +2088,12 @@ static void f2fs_put_super(struct super_block *sb)
#if IS_ENABLED(CONFIG_UNICODE)
utf8_unload(sb->s_encoding);
#endif
+ sync_blockdev(sb->s_bdev);
+ invalidate_bdev(sb->s_bdev);
+ for (i = 1; i < sbi->s_ndevs; i++) {
+ sync_blockdev(FDEV(i).bdev);
+ invalidate_bdev(FDEV(i).bdev);
+ }
}
int f2fs_sync_fs(struct super_block *sb, int sync)
--
2.43.0
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