New locking paradigm for fellow_cache_lru_work

src/fellow_cache.c

@@ -2988,7 +2988,17 @@ fellow_cache_lru_work(struct worker *wrk, struct fellow_cache_lru *lru)
 	struct buddy_ptr_extent alloc;
 	int r;
 
-	//lint --e{456} flexelint does not grok trylock
+	/*lint --e{454,455,456}
+	 *
+	 * flexelint does not understand the locking structure here:
+	 *
+	 * - it dies not understand trylock
+	 * - we leave the loop either with break
+	 *   - mtx unlocked
+	 *   - fcs != NULL
+	 * - or foreach finishes, then fcs == NULL and the mtx
+	 *   needs to be unlocked
+	 */
 
 	CHECK_OBJ_NOTNULL(lru, FELLOW_CACHE_LRU_MAGIC);
 	buddy = lru->fc->membuddy;
@@ -3012,6 +3022,7 @@ fellow_cache_lru_work(struct worker *wrk, struct fellow_cache_lru *lru)
 			fellow_cache_lru_seg_evict_locked(fcs,
 			    &alloc, lru);
 			AZ(pthread_mutex_unlock(&fco->mtx));
+			AZ(pthread_mutex_unlock(&lru->lru_mtx));
 			fco = NULL;
 			break;
 		}
@@ -3024,6 +3035,7 @@ fellow_cache_lru_work(struct worker *wrk, struct fellow_cache_lru *lru)
 				/* mutate was successful
 				 * VSC_C_main->n_lru_nuked++; // XXX per lru ?
 				 */
+				AZ(pthread_mutex_unlock(&lru->lru_mtx));
 				break;
 			}
 			oc = NULL;
@@ -3033,9 +3045,9 @@ fellow_cache_lru_work(struct worker *wrk, struct fellow_cache_lru *lru)
 		AZ(pthread_mutex_unlock(&fco->mtx));
 		WRONG("fcs state in lru");
 	}
-	AZ(pthread_mutex_unlock(&lru->lru_mtx));
 
 	if (fcs == NULL) {
+		AZ(pthread_mutex_unlock(&lru->lru_mtx));
 //		VSLb(wrk->vsl, SLT_ExpKill, "LRU_Fail");
 		AZ(alloc.ptr);
 		AZ(oc);