On Fri, Mar 08, 2024 at 09:53:07PM +0530, Anand Jain wrote: > It's a bit complex, as Boris discovered and has provided a testcase > for here: > > https://lore.kernel.org/fstests/f40e347d5a4b4b28201b1a088d38a3c75dd10ebd.1709251328.git.boris@xxxxxx/ > > In essence: > > - Create two devices, d1 and d2. > - Both devices will be scanned into the kernel by Mfks. > - Use an external method to alter the devt of the d2 device. > - Mount using d1. > - You end up with a 2 devices Btrfs with an incorrect device->devt. > - Delete d1. > - Now you have a single-device Btrfs on d2 with a stale device->devt. But how do you get mismatching devices in this exact place? - bdev->bd_dev is immutable and never updated - device->devt can be changed by device_list_add, but if that happens underneath us here between btrfs_get_bdev_and_sb and the code a few lines below the call to it in btrfs_open_one_device there is a huge synchronization problem
