btrfs: deny freezing a device while it is being added

btrfs_init_new_device() opens and claims the new device on a live
superblock without holding the write count, so a bdev_freeze() racing the
window between the claim being published and the device becoming a member
could freeze the filesystem through a claim the add may still abort and tear
down.

Add btrfs_open_device_deny_freeze(): it opens the device once
non-exclusively to take the freeze deny, then claims it by the same dev_t,
so the holder is only ever published while the device is already
unfreezable.  Keep it denied until the add is durable: bdev_allow_freeze()
on each success return (the device is now a committed member),
btrfs_release_device_allow_freeze() on the error unwind.  The deny spans the
whole add, including the seeding tail whose late failures still release the
device.  A device already frozen when the add starts is refused with -EBUSY.

Link: https://patch.msgid.link/20260616-work-super-freeze_deny_upstream-v2-4-b3567c7f994b@kernel.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions