sb_getblk does not guarantee that buffer_head is uptodate. If there is
async read running in parallel for same buffer_head, it can overwrite
just initialized msdos_dir_entry, leading to corruption:
FAT-fs (loop0): error, corrupted directory (invalid entries)
FAT-fs (loop0): Filesystem has been set read-only
This can happen for example during LTP statx04, which creates loop
device, formats it (mkfs.vfat), mounts it and immediately creates
a new directory. In parallel, systemd-udevd is probing new block
device, which leads to async read.
do_mkdirat ksys_read
vfs_mkdir vfs_read
vfat_mkdir __vfs_read
fat_alloc_new_dir new_sync_read
/* init de[0], de[1] */ blkdev_read_iter
generic_file_read_iter
generic_file_buffered_read
blkdev_readpage
block_read_full_page
Faster reproducer (based on LTP statx04):
--------------------------------- 8< ---------------------------------
int main(void)
{
int i, j, ret, fd, loop_fd, ctrl_fd;
int loop_num;
char loopdev[256], tmp[256], testfile[256];
mkdir("/tmp/mntpoint", 0777);
for (i = 0; ; i++) {
printf("Iteration: %d\n", i);
sprintf(testfile, "/tmp/test.img.%d", getpid());
ctrl_fd = open("/dev/loop-control", O_RDWR);
loop_num = ioctl(ctrl_fd, LOOP_CTL_GET_FREE);
close(ctrl_fd);
sprintf(loopdev, "/dev/loop%d", loop_num);
fd = open(testfile, O_WRONLY|O_CREAT|O_TRUNC, 0600);
fallocate(fd, 0, 0, 256*1024*1024);
close(fd);
fd = open(testfile, O_RDWR);
loop_fd = open(loopdev, O_RDWR);
ioctl(loop_fd, LOOP_SET_FD, fd);
close(loop_fd);
close(fd);
sprintf(tmp, "mkfs.vfat %s", loopdev);
system(tmp);
mount(loopdev, "/tmp/mntpoint", "vfat", 0, NULL);
for (j = 0; j < 200; j++) {
sprintf(tmp, "/tmp/mntpoint/testdir%d", j);
ret = mkdir(tmp, 0777);
if (ret) {
perror("mkdir");
break;
}
}
umount("/tmp/mntpoint");
loop_fd = open(loopdev, O_RDWR);
ioctl(loop_fd, LOOP_CLR_FD, fd);
close(loop_fd);
unlink(testfile);
if (ret)
break;
}
return 0;
}
--------------------------------- 8< ---------------------------------
Issue triggers within minute on HPE Apollo 70 (arm64, 64GB RAM, 224 CPUs).
Signed-off-by: Jan Stancek <jstan...@redhat.com>
Cc: OGAWA Hirofumi <hirof...@mail.parknet.co.jp>
---
fs/fat/dir.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/fat/dir.c b/fs/fat/dir.c
index 1bda2ab6745b..474fd6873ec8 100644
--- a/fs/fat/dir.c
+++ b/fs/fat/dir.c
@@ -1149,7 +1149,7 @@ int fat_alloc_new_dir(struct inode *dir, struct
timespec64 *ts)
goto error;
blknr = fat_clus_to_blknr(sbi, cluster);
- bhs[0] = sb_getblk(sb, blknr);
+ bhs[0] = sb_bread(sb, blknr);
if (!bhs[0]) {
err = -ENOMEM;
goto error_free;
--
1.8.3.1
