[PATCH 1.10 1/2] vinyl: clean up region after allocating surrogate statement

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

vy_stmt_new_surrogate_from_key() and vy_stmt_new_surrogate_delete_raw()
allocate temporary objects on the region, but don't clean up after
themselves. Those functions may be called by a vinyl reader threads:

  vy_page_read_cb
    vy_page_find_key
      vy_page_stmt
        vy_stmt_decode

In this case the region will grow infinitely, because reader threads
never call fiber_gc().

The leak was introduced to 1.10 by commit b907231713a7 ("vinyl: lookup
key in reader thread"), which moved vy_page_find_key() invocation to
reader threads for the sake of performance. The fix is trivial - call
region_truncate() from those functions.

Note, neither the master branch nor 2.1 is affected to this issue,
because region_truncate() was added there in the scope of the multikey
index feature.
---
 src/box/vy_stmt.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/box/vy_stmt.c b/src/box/vy_stmt.c
index ca4c55f4..9b7c5551 100644
--- a/src/box/vy_stmt.c
+++ b/src/box/vy_stmt.c
@@ -383,6 +383,7 @@ vy_stmt_new_surrogate_from_key(const char *key, enum iproto_type type,
 	/* UPSERT can't be surrogate. */
 	assert(type != IPROTO_UPSERT);
 	struct region *region = &fiber()->gc;
+	size_t region_svp = region_used(region);
 
 	uint32_t field_count = format->index_field_count;
 	struct iovec *iov = region_alloc(region, sizeof(*iov) * field_count);
@@ -410,7 +411,7 @@ vy_stmt_new_surrogate_from_key(const char *key, enum iproto_type type,
 
 	struct tuple *stmt = vy_stmt_alloc(format, bsize);
 	if (stmt == NULL)
-		return NULL;
+		goto out;
 
 	char *raw = (char *) tuple_data(stmt);
 	uint32_t *field_map = (uint32_t *) raw;
@@ -428,6 +429,8 @@ vy_stmt_new_surrogate_from_key(const char *key, enum iproto_type type,
 	}
 	assert(wpos == raw + bsize);
 	vy_stmt_set_type(stmt, type);
+out:
+	region_truncate(region, region_svp);
 	return stmt;
 }
 
@@ -443,10 +446,13 @@ struct tuple *
 vy_stmt_new_surrogate_delete_raw(struct tuple_format *format,
 				 const char *src_data, const char *src_data_end)
 {
+	struct region *region = &fiber()->gc;
+	size_t region_svp = region_used(region);
+
 	uint32_t src_size = src_data_end - src_data;
 	uint32_t total_size = src_size + format->field_map_size;
 	/* Surrogate tuple uses less memory than the original tuple */
-	char *data = region_alloc(&fiber()->gc, total_size);
+	char *data = region_alloc(region, total_size);
 	if (data == NULL) {
 		diag_set(OutOfMemory, src_size, "region", "tuple");
 		return NULL;
@@ -490,13 +496,14 @@ vy_stmt_new_surrogate_delete_raw(struct tuple_format *format,
 	uint32_t bsize = pos - data;
 	struct tuple *stmt = vy_stmt_alloc(format, bsize);
 	if (stmt == NULL)
-		return NULL;
+		goto out;
 	char *stmt_data = (char *) tuple_data(stmt);
 	char *stmt_field_map_begin = stmt_data - format->field_map_size;
 	memcpy(stmt_data, data, bsize);
 	memcpy(stmt_field_map_begin, field_map_begin, format->field_map_size);
 	vy_stmt_set_type(stmt, IPROTO_DELETE);
-
+out:
+	region_truncate(region, region_svp);
 	return stmt;
 }
 
-- 
2.11.0