On Wed, Feb 08, 2023 at 01:57:42PM +0800, Ziyang Zhang wrote: > On 2023/2/7 23:07, Ming Lei wrote: > > Inside ublk_ctrl_del_dev(), when the device is removed, we wait > > until the device number is freed with holding global lock of > > ublk_ctl_mutex, this way isn't friendly from user viewpoint: > > > > 1) if device is in-use, the current delete command hangs in > > ublk_ctrl_del_dev(), and user can't break from the handling > > because wait_event() is used > > > > 2) global lock is held, so any new device can't be added and > > other old devices can't be removed. > > > > Improve the deleting handling by the following way, suggested by > > Nadav: > > > > 1) wait without holding the global lock > > > > 2) replace wait_event() with wait_event_interruptible() > > > > Reported-by: Nadav Amit <nadav.amit@xxxxxxxxx> > > Suggested-by: Nadav Amit <nadav.amit@xxxxxxxxx> > > Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx> > > Hi Ming, > > I tried this patch. And the folloing NPE bug was trigged by: > > (0) dd if=/dev/zero of=/root/img bs=4096 count=1024768 > (1) ublk add -t loop -f /root/img > (2) mkdir -p /root/ublk > (3) mount /dev/ublkb0 /root/ublk > (4) echo "hello" > /root/ublk > (5) ./ublk del -n 0 > > So I delete the ublk device while it is mounting as > an ext4 filesystem. I think ublk should handle this > by (1) returning -EBUSY or (2) blocking incoming IO. That isn't ublk unique, and is one recent block layer regression, see the following report: https://lore.kernel.org/linux-block/20230208063552.GA15030@xxxxxx/T/#u Thanks, Ming
