lru_cache: use atomic operations when accessing lc->flags, always

Or, depending on the way locking is implemented at the call sites,
some updates could be lost (has not been observed).
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Link: https://lore.kernel.org/r/20221122134301.69258-2-christoph.boehmwalder@linbit.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

lib/lru_cache.c

@@ -364,7 +364,7 @@ static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, unsig
 	struct lc_element *e;
 
 	PARANOIA_ENTRY();
-	if (lc->flags & LC_STARVING) {
+	if (test_bit(__LC_STARVING, &lc->flags)) {
 		++lc->starving;
 		RETURN(NULL);
 	}
@@ -417,7 +417,7 @@ static struct lc_element *__lc_get(struct lru_cache *lc, unsigned int enr, unsig
 	 * the LRU element, we have to wait ...
 	 */
 	if (!lc_unused_element_available(lc)) {
-		__set_bit(__LC_STARVING, &lc->flags);
+		set_bit(__LC_STARVING, &lc->flags);
 		RETURN(NULL);
 	}