dlm: fix sleep in atomic context

This patch changes the orphans mutex to a spinlock since commit
c288745f1d4a ("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 92d59adfaf71
("dlm: do message processing in softirq context") the DLM message
receive path is done under softirq context.

Fixes: c288745f1d4a ("dlm: avoid blocking receive at the end of recovery")
Reported-by: Dan Carpenter <[e-mail]>
Closes: https://lore.kernel.org/gfs2/[e-mail]/
Signed-off-by: Alexander Aring <[e-mail]>
Signed-off-by: David Teigland <[e-mail]>

fs/dlm/dlm_internal.h

···
 	spinlock_t		ls_waiters_lock;
 	struct list_head	ls_waiters;	/* lkbs needing a reply */
 
-	struct mutex		ls_orphans_mutex;
+	spinlock_t		ls_orphans_lock;
 	struct list_head	ls_orphans;
 
 	spinlock_t		ls_new_rsb_spin;

fs/dlm/lock.c

···
 	int found_other_mode = 0;
 	int rv = 0;
 
-	mutex_lock(&ls->ls_orphans_mutex);
+	spin_lock_bh(&ls->ls_orphans_lock);
 	list_for_each_entry(iter, &ls->ls_orphans, lkb_ownqueue) {
 		if (iter->lkb_resource->res_length != namelen)
 			continue;
···
 		*lkid = iter->lkb_id;
 		break;
 	}
-	mutex_unlock(&ls->ls_orphans_mutex);
+	spin_unlock_bh(&ls->ls_orphans_lock);
 
 	if (!lkb && found_other_mode) {
 		rv = -EAGAIN;
···
 	int error;
 
 	hold_lkb(lkb); /* reference for the ls_orphans list */
-	mutex_lock(&ls->ls_orphans_mutex);
+	spin_lock_bh(&ls->ls_orphans_lock);
 	list_add_tail(&lkb->lkb_ownqueue, &ls->ls_orphans);
-	mutex_unlock(&ls->ls_orphans_mutex);
+	spin_unlock_bh(&ls->ls_orphans_lock);
 
 	set_unlock_args(0, lkb->lkb_ua, &args);
 
···
 {
 	struct dlm_lkb *lkb, *safe;
 
-	mutex_lock(&ls->ls_orphans_mutex);
+	spin_lock_bh(&ls->ls_orphans_lock);
 	list_for_each_entry_safe(lkb, safe, &ls->ls_orphans, lkb_ownqueue) {
 		if (pid && lkb->lkb_ownpid != pid)
 			continue;
···
 		list_del_init(&lkb->lkb_ownqueue);
 		dlm_put_lkb(lkb);
 	}
-	mutex_unlock(&ls->ls_orphans_mutex);
+	spin_unlock_bh(&ls->ls_orphans_lock);
 }
 
 static int send_purge(struct dlm_ls *ls, int nodeid, int pid)

fs/dlm/lockspace.c

···
 	INIT_LIST_HEAD(&ls->ls_waiters);
 	spin_lock_init(&ls->ls_waiters_lock);
 	INIT_LIST_HEAD(&ls->ls_orphans);
-	mutex_init(&ls->ls_orphans_mutex);
+	spin_lock_init(&ls->ls_orphans_lock);
 
 	INIT_LIST_HEAD(&ls->ls_new_rsb);
 	spin_lock_init(&ls->ls_new_rsb_spin);