[PATCH 1/4] vinyl: fix EQ check in run iterator

[Vladimir Davydov <vdavydov.dev@gmail.com>]

vy_run_iterator_seek() is supposed to check that the resulting statement
matches the search key in case of ITER_EQ, but if the search key lies at
the beginning of the slice, it doesn't. As a result, vy_point_lookup()
may fail to find an existing tuple as demonstrated below.

Suppose we are looking for key {10} in the primary index which consists
of an empty mem and two runs:

    run 1: DELETE{15}
    run 2: INSERT{10}

vy_run_iterator_next() returns DELETE{15} for run 1 because of the
missing EQ check and vy_point_lookup() stops at run 1 (since the
terminal statement is found) and mistakenly returns NULL.

The issue manifests itself as crash in vinyl_iterator_secondary_next(),
when we fail to find the tuple in the primary index corresponding to a
statement found in a secondary index.

Part of #3393
---
 src/box/vy_run.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/box/vy_run.c b/src/box/vy_run.c
index 587cb002..8c922895 100644
--- a/src/box/vy_run.c
+++ b/src/box/vy_run.c
@@ -1316,6 +1316,7 @@ vy_run_iterator_seek(struct vy_run_iterator *itr,
 {
 	const struct key_def *cmp_def = itr->cmp_def;
 	struct vy_slice *slice = itr->slice;
+	const struct tuple *check_eq_key = NULL;
 	int cmp;
 
 	if (slice->begin != NULL &&
@@ -1340,6 +1341,8 @@ vy_run_iterator_seek(struct vy_run_iterator *itr,
 			return 0;
 		}
 		if (cmp < 0 || (cmp == 0 && iterator_type != ITER_GT)) {
+			if (iterator_type == ITER_EQ)
+				check_eq_key = key;
 			iterator_type = ITER_GE;
 			key = slice->begin;
 		}
@@ -1365,7 +1368,15 @@ vy_run_iterator_seek(struct vy_run_iterator *itr,
 		}
 	}
 
-	return vy_run_iterator_do_seek(itr, iterator_type, key, ret);
+	if (vy_run_iterator_do_seek(itr, iterator_type, key, ret) != 0)
+		return -1;
+
+	if (check_eq_key != NULL && *ret != NULL &&
+	    vy_stmt_compare(check_eq_key, *ret, cmp_def) != 0) {
+		vy_run_iterator_stop(itr);
+		*ret = NULL;
+	}
+	return 0;
 }
 
 /* }}} vy_run_iterator vy_run_iterator support functions */
-- 
2.11.0