> Currently, if we freeze a filesystem with "fsfreeze" and unmount it, the > mount point is removed, but the filesystem stays active and it is leaked. > You can't unfreeze it with "fsfreeze --unfreeze" because the mount point > is gone. (the only way how to recover it is "echo j>/proc/sysrq-trigger"). You can of course always remount and unfreeze it. > > IOW, you'd also hang on any umount of a bind-mount. IOW, every > > single container making use of this filesystems via bind-mounts would > > hang on umount and shutdown. > > bind-mount doesn't modify "s->s_writers.frozen", so the patch does nothing > in this case. I tried unmounting bind-mounts and there was no deadlock. With your patch what happens if you do the following? #!/bin/sh -ex modprobe brd rd_size=4194304 vgcreate vg /dev/ram0 lvcreate -L 16M -n lv vg mkfs.ext4 /dev/vg/lv mount -t ext4 /dev/vg/lv /mnt/test mount --bind /mnt/test /opt mount --make-private /opt dmsetup suspend /dev/vg/lv (sleep 1; dmsetup resume /dev/vg/lv) & umount /opt # I'd expect this to hang md5sum /dev/vg/lv md5sum /dev/vg/lv dmsetup remove_all rmmod brd > BTW. what do you think that unmount of a frozen filesystem should properly > do? Fail with -EBUSY? Or, unfreeze the filesystem and unmount it? Or > something else? In my opinion we should refuse to unmount frozen filesystems and log an error that the filesystem is frozen. Waiting forever isn't a good idea in my opinion. But this is a significant uapi change afaict so this would need to be hidden behind a config option, a sysctl, or it would have to be a new flag to umount2() MNT_UNFROZEN which would allow an administrator to use this flag to not unmount a frozen filesystems.
