This patch changes the orphans mutex to a spinlock since commit
c288745f ("dlm: avoid blocking receive at the end of recovery") is
using a rwlock_t to lock the DLM message receive path and do_purge() can
be called while this lock is held that forbids to sleep.

We need to use spin_lock_bh() because also a user context that calls
dlm_user_purge() can call do_purge() and since commit 92d59adf
("dlm: do message processing in softirq context") the DLM message
receive path is done under softirq context.

Fixes: c288745f ("dlm: avoid blocking receive at the end of recovery")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/gfs2/9ad928eb-2ece-4ad9-a79c-d2bce228e4bc@moroto.mountain/Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>