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