On Mon, Apr 03, 2023 at 01:46:08PM +0800, Anand Jain wrote:
commit 50d281fc434cb8e2497f5e70a309ccca6b1a09f0 upstream.
This fixes mkfs/mount/check failures due to race with systemd-udevd scan.
During the device scan initiated by systemd-udevd, other user space EXCL operations such as mkfs, mount, or check may get blocked and result in a "Device or resource busy" error. This is because the device scan process opens the device with the EXCL flag in the kernel.
Two reports were received:
btrfs/179 test case, where the fsck command failed with the -EBUSY error
LTP pwritev03 test case, where mkfs.vfs failed with the -EBUSY error, when mkfs.vfs tried to overwrite old btrfs filesystem on the device.
In both cases, fsck and mkfs (respectively) were racing with a systemd-udevd device scan, and systemd-udevd won, resulting in the -EBUSY error for fsck and mkfs.
Reproducing the problem has been difficult because there is a very small window during which these userspace threads can race to acquire the exclusive device open. Even on the system where the problem was observed, the problem occurrences were anywhere between 10 to 400 iterations and chances of reproducing decreases with debug printk()s.
However, an exclusive device open is unnecessary for the scan process, as there are no write operations on the device during scan. Furthermore, during the mount process, the superblock is re-read in the below function call chain:
btrfs_mount_root btrfs_open_devices open_fs_devices btrfs_open_one_device btrfs_get_bdev_and_sb
So, to fix this issue, removes the FMODE_EXCL flag from the scan operation, and add a comment.
The case where mkfs may still write to the device and a scan is running, the btrfs signature is not written at that time so scan will not recognize such device.
Reported-by: Sherry Yang sherry.yang@oracle.com Reported-by: kernel test robot oliver.sang@intel.com Link: https://lore.kernel.org/oe-lkp/202303170839.fdf23068-oliver.sang@intel.com CC: stable@vger.kernel.org # 5.4+ Signed-off-by: Anand Jain anand.jain@oracle.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Anand Jain anand.jain@oracle.com
The upstream commit 50d281fc434cb8e2497f5e70a309ccca6b1a09f0 can be applied without conflict to LTS stable-5.15.y and stable-6.1.y. However, on LTS stable-5.4.y and stable-5.15.y, a conflict fix is required since the zoned device support commits are not present in these versions. This patch resolves the conflicts.
Now queued up, thanks.
greg k-h