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
