Avoid bad sparse warning in lock_invalidate()

This is another example of refactoring a loop to avoid sparse warnings
from doing something in the else of a failed trylock if.  We want to
drop and reacquire the lock if the trylock fails so we do it every loop
iteration.  This shouldn't be experiencing much contention because most
of the cov users are usually done under locks and invalidation has
excluded lock holders.  So the additional lock and unlock noise should
be local.

Signed-off-by: Zach Brown <zab@versity.com>

kmod/src/lock.c

@@ -168,7 +168,6 @@ static int lock_invalidate(struct super_block *sb, struct scoutfs_lock *lock,
 			   enum scoutfs_lock_mode prev, enum scoutfs_lock_mode mode)
 {
 	struct scoutfs_lock_coverage *cov;
-	struct scoutfs_lock_coverage *tmp;
 	u64 ino, last;
 	int ret = 0;
 
@@ -192,19 +191,22 @@ static int lock_invalidate(struct super_block *sb, struct scoutfs_lock *lock,
 
 	/* have to invalidate if we're not in the only usable case */
 	if (!(prev == SCOUTFS_LOCK_WRITE && mode == SCOUTFS_LOCK_READ)) {
-retry:
-		/* remove cov items to tell users that their cache is stale */
+		/*
+		 * Remove cov items to tell users that their cache is
+		 * stale.  The unlock pattern comes from avoiding bad
+		 * sparse warnings when taking else in a failed trylock.
+		 */
 		spin_lock(&lock->cov_list_lock);
-		list_for_each_entry_safe(cov, tmp, &lock->cov_list, head) {
-			if (!spin_trylock(&cov->cov_lock)) {
-				spin_unlock(&lock->cov_list_lock);
-				cpu_relax();
-				goto retry;
+		while ((cov = list_first_entry_or_null(&lock->cov_list,
+						       struct scoutfs_lock_coverage, head))) {
+			if (spin_trylock(&cov->cov_lock)) {
+				list_del_init(&cov->head);
+				cov->lock = NULL;
+				spin_unlock(&cov->cov_lock);
+				scoutfs_inc_counter(sb, lock_invalidate_coverage);
 			}
-			list_del_init(&cov->head);
-			cov->lock = NULL;
-			spin_unlock(&cov->cov_lock);
-			scoutfs_inc_counter(sb, lock_invalidate_coverage);
+			spin_unlock(&lock->cov_list_lock);
+			spin_lock(&lock->cov_list_lock);
 		}
 		spin_unlock(&lock->cov_list_lock);