Ping? Any opinion? Honza On Thu 13-01-22 16:47:35, Jan Kara wrote: > Hello, > > Tetsuo has been doing some changes to the loop device shutdown in the > kernel and that broke LTP that is doing essentially the following loop: > > while :; do mount -o loop,ro isofs.iso isofs/; umount isofs/; done > > And this loop is broken because of a subtle interaction with systemd-udev > that also opens the loop device. The race seems to be in mount(8) handling > itself and the altered kernel timing makes it happen. It look like: > > bash systemd-udev > mount -o loop,ro isofs.iso isofs/ > /dev/loop0 is created and bound to isofs.iso, autoclear is set for > loop0 > opens /dev/loop0 > umount isofs/ > loop0 still lives because systemd-udev still has device open > mount -o loop,ro isofs.iso isofs/ > gets to mnt_context_setup_loopdev() > loopcxt_find_overlap() > sees loop0 is still valid and with proper parameters > reuse = true; > close /dev/loop0 > last fd closed => loop0 is > cleaned up > loopcxt_get_fd() > opens loop0 but it is no longer the device we wanted! > calls mount(2) which fails because we cannot read from the loop device > > It seems to me that mnt_context_setup_loopdev() should actually recheck > that loop device parameters still match what we need after opening > /dev/loop0 (if LOOP_GET_STATUS ioctl succeeds on the fd, you are guaranteed > the loop device is in that state and will not be torn down under your > hands). What do you think? > > Honza > -- > Jan Kara <jack@xxxxxxxx> > SUSE Labs, CR -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
