fs: dlm: handle lkb wait count as atomic_t

Currently the lkb_wait_count is locked by the rsb lock and it should be
fine to handle lkb_wait_count as non atomic_t value. However for the
overall process of reducing locking this patch converts it to an
atomic_t value.

Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

Author: Alexander Aring

fs/dlm/dlm_internal.h

@@ -246,7 +246,7 @@ struct dlm_lkb {
 	int8_t			lkb_highbast;	/* highest mode bast sent for */
 
 	int8_t			lkb_wait_type;	/* type of reply waiting for */
-	int8_t			lkb_wait_count;
+	atomic_t		lkb_wait_count;
 	int			lkb_wait_nodeid; /* for debugging */
 
 	struct list_head	lkb_statequeue;	/* rsb g/c/w list */

fs/dlm/lock.c

@@ -1407,6 +1407,7 @@ static int add_to_waiters(struct dlm_lkb *lkb, int mstype, int to_nodeid)
 {
 	struct dlm_ls *ls = lkb->lkb_resource->res_ls;
 	int error = 0;
+	int wc;
 
 	mutex_lock(&ls->ls_waiters_mutex);
 
@@ -1428,20 +1429,17 @@ static int add_to_waiters(struct dlm_lkb *lkb, int mstype, int to_nodeid)
 			error = -EBUSY;
 			goto out;
 		}
-		lkb->lkb_wait_count++;
+		wc = atomic_inc_return(&lkb->lkb_wait_count);
 		hold_lkb(lkb);
 
 		log_debug(ls, "addwait %x cur %d overlap %d count %d f %x",
-			  lkb->lkb_id, lkb->lkb_wait_type, mstype,
-			  lkb->lkb_wait_count, dlm_iflags_val(lkb));
+			  lkb->lkb_id, lkb->lkb_wait_type, mstype, wc,
+			  dlm_iflags_val(lkb));
 		goto out;
 	}
 
-	DLM_ASSERT(!lkb->lkb_wait_count,
-		   dlm_print_lkb(lkb);
-		   printk("wait_count %d\n", lkb->lkb_wait_count););
-
-	lkb->lkb_wait_count++;
+	wc = atomic_fetch_inc(&lkb->lkb_wait_count);
+	DLM_ASSERT(!wc, dlm_print_lkb(lkb); printk("wait_count %d\n", wc););
 	lkb->lkb_wait_type = mstype;
 	lkb->lkb_wait_nodeid = to_nodeid; /* for debugging */
 	hold_lkb(lkb);
@@ -1504,7 +1502,7 @@ static int _remove_from_waiters(struct dlm_lkb *lkb, int mstype,
 		log_debug(ls, "remwait %x convert_reply zap overlap_cancel",
 			  lkb->lkb_id);
 		lkb->lkb_wait_type = 0;
-		lkb->lkb_wait_count--;
+		atomic_dec(&lkb->lkb_wait_count);
 		unhold_lkb(lkb);
 		goto out_del;
 	}
@@ -1531,16 +1529,15 @@ static int _remove_from_waiters(struct dlm_lkb *lkb, int mstype,
 	if (overlap_done && lkb->lkb_wait_type) {
 		log_error(ls, "remwait error %x reply %d wait_type %d overlap",
 			  lkb->lkb_id, mstype, lkb->lkb_wait_type);
-		lkb->lkb_wait_count--;
+		atomic_dec(&lkb->lkb_wait_count);
 		unhold_lkb(lkb);
 		lkb->lkb_wait_type = 0;
 	}
 
-	DLM_ASSERT(lkb->lkb_wait_count, dlm_print_lkb(lkb););
+	DLM_ASSERT(atomic_read(&lkb->lkb_wait_count), dlm_print_lkb(lkb););
 
 	clear_bit(DLM_IFL_RESEND_BIT, &lkb->lkb_iflags);
-	lkb->lkb_wait_count--;
-	if (!lkb->lkb_wait_count)
+	if (atomic_dec_and_test(&lkb->lkb_wait_count))
 		list_del_init(&lkb->lkb_wait_reply);
 	unhold_lkb(lkb);
 	return 0;
@@ -2669,7 +2666,7 @@ static int validate_lock_args(struct dlm_ls *ls, struct dlm_lkb *lkb,
 			goto out;
 
 		/* lock not allowed if there's any op in progress */
-		if (lkb->lkb_wait_type || lkb->lkb_wait_count)
+		if (lkb->lkb_wait_type || atomic_read(&lkb->lkb_wait_count))
 			goto out;
 
 		if (is_overlap(lkb))
@@ -2731,7 +2728,7 @@ static int validate_unlock_args(struct dlm_lkb *lkb, struct dlm_args *args)
 
 	/* normal unlock not allowed if there's any op in progress */
 	if (!(args->flags & (DLM_LKF_CANCEL | DLM_LKF_FORCEUNLOCK)) &&
-	    (lkb->lkb_wait_type || lkb->lkb_wait_count))
+	    (lkb->lkb_wait_type || atomic_read(&lkb->lkb_wait_count)))
 		goto out;
 
 	/* an lkb may be waiting for an rsb lookup to complete where the
@@ -5066,10 +5063,9 @@ int dlm_recover_waiters_post(struct dlm_ls *ls)
 		/* drop all wait_count references we still
 		 * hold a reference for this iteration.
 		 */
-		while (lkb->lkb_wait_count) {
-			lkb->lkb_wait_count--;
+		while (!atomic_dec_and_test(&lkb->lkb_wait_count))
 			unhold_lkb(lkb);
-		}
+
 		mutex_lock(&ls->ls_waiters_mutex);
 		list_del_init(&lkb->lkb_wait_reply);
 		mutex_unlock(&ls->ls_waiters_mutex);