fs: dlm: use spin lock instead of mutex

There is no need to use a mutex in those hot path sections. We change it
to spin lock to serve callbacks more faster by not allowing schedule.
The locked sections will not be locked for a long time.
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/ast.c

@@ -190,7 +190,7 @@ void dlm_add_cb(struct dlm_lkb *lkb, uint32_t flags, int mode, int status,
 		return;
 	}
 
-	mutex_lock(&lkb->lkb_cb_mutex);
+	spin_lock(&lkb->lkb_cb_lock);
 	prev_seq = lkb->lkb_callbacks[0].seq;
 
 	rv = dlm_add_lkb_callback(lkb, flags, mode, status, sbflags, new_seq);
@@ -209,7 +209,7 @@ void dlm_add_cb(struct dlm_lkb *lkb, uint32_t flags, int mode, int status,
 		spin_unlock(&ls->ls_cb_lock);
 	}
  out:
-	mutex_unlock(&lkb->lkb_cb_mutex);
+	spin_unlock(&lkb->lkb_cb_lock);
 }
 
 void dlm_callback_work(struct work_struct *work)
@@ -223,7 +223,7 @@ void dlm_callback_work(struct work_struct *work)
 
 	memset(&callbacks, 0, sizeof(callbacks));
 
-	mutex_lock(&lkb->lkb_cb_mutex);
+	spin_lock(&lkb->lkb_cb_lock);
 	if (!lkb->lkb_callbacks[0].seq) {
 		/* no callback work exists, shouldn't happen */
 		log_error(ls, "dlm_callback_work %x no work", lkb->lkb_id);
@@ -244,7 +244,7 @@ void dlm_callback_work(struct work_struct *work)
 		dlm_print_lkb(lkb);
 		dlm_dump_lkb_callbacks(lkb);
 	}
-	mutex_unlock(&lkb->lkb_cb_mutex);
+	spin_unlock(&lkb->lkb_cb_lock);
 
 	castfn = lkb->lkb_astfn;
 	bastfn = lkb->lkb_bastfn;

fs/dlm/dlm_internal.h

@@ -268,7 +268,7 @@ struct dlm_lkb {
 	unsigned long		lkb_timeout_cs;
 #endif
 
-	struct mutex		lkb_cb_mutex;
+	spinlock_t		lkb_cb_lock;
 	struct work_struct	lkb_cb_work;
 	struct list_head	lkb_cb_list; /* for ls_cb_delay or proc->asts */
 	struct dlm_callback	lkb_callbacks[DLM_CALLBACKS_SIZE];

fs/dlm/lock.c

@@ -1218,7 +1218,7 @@ static int _create_lkb(struct dlm_ls *ls, struct dlm_lkb **lkb_ret,
 	INIT_LIST_HEAD(&lkb->lkb_time_list);
 #endif
 	INIT_LIST_HEAD(&lkb->lkb_cb_list);
-	mutex_init(&lkb->lkb_cb_mutex);
+	spin_lock_init(&lkb->lkb_cb_lock);
 	INIT_WORK(&lkb->lkb_cb_work, dlm_callback_work);
 
 	idr_preload(GFP_NOFS);