staging: lustre: obdclass: hoist locking in lu_context_exit()

Hoist lu_keys_guard locking out of the for loop in lu_context_exit().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-8918
Reviewed-on: https://review.whamcloud.com/24217
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/obdclass/lu_object.c

@@ -1721,10 +1721,11 @@ void lu_context_exit(struct lu_context *ctx)
 	LINVRNT(ctx->lc_state == LCS_ENTERED);
 	ctx->lc_state = LCS_LEFT;
 	if (ctx->lc_tags & LCT_HAS_EXIT && ctx->lc_value) {
+		/* could race with key quiescency */
+		if (ctx->lc_tags & LCT_REMEMBER)
+			read_lock(&lu_keys_guard);
+
 		for (i = 0; i < ARRAY_SIZE(lu_keys); ++i) {
-			/* could race with key quiescency */
-			if (ctx->lc_tags & LCT_REMEMBER)
-				read_lock(&lu_keys_guard);
 			if (ctx->lc_value[i]) {
 				struct lu_context_key *key;
 
@@ -1733,9 +1734,10 @@ void lu_context_exit(struct lu_context *ctx)
 					key->lct_exit(ctx,
 						      key, ctx->lc_value[i]);
 			}
-			if (ctx->lc_tags & LCT_REMEMBER)
-				read_unlock(&lu_keys_guard);
 		}
+
+		if (ctx->lc_tags & LCT_REMEMBER)
+			read_unlock(&lu_keys_guard);
 	}
 }
 EXPORT_SYMBOL(lu_context_exit);