On Tue, May 06, 2025 at 03:36:03PM +0200, Klara Modin wrote: > 25: 49 8b 44 24 60 mov 0x60(%r12),%rax rax = fc->root > 2a:* 48 8b 78 68 mov 0x68(%rax),%rdi <-- trapping instruction rdi = rax->d_sb, hitting rax == 0 > > - mnt = fc_mount(dup_fc); > > - if (IS_ERR(mnt)) { > > - put_fs_context(dup_fc); > > - return PTR_ERR(mnt); > > + ret = vfs_get_tree(dup_fc); > > + if (!ret) { > > + ret = btrfs_reconfigure_for_mount(dup_fc); > > + up_write(&fc->root->d_sb->s_umount); ... here. D'oh... Should be dup_fc, obviously - fc->root hadn't been set yet. Make that line up_write(&dup_fc->root->d_sb->s_umount); and see if it helps. Sorry about the braino...