Make the odb race-free

This change adds all the necessary locking to the odb to avoid races in
the backends.

Part of: #5592

script/thread-sanitizer.supp

@@ -8,11 +8,6 @@ deadlock:attr_cache_lock
 # data races.
 called_from_lib:libc.so.6
 
-# TODO(#5595): Remove these once the fixes land.
-race:src/odb.c
-race:git_repository_odb__weakptr
-race:cache_store
-
-# TODO(#5595): Investigate and fix this. It can be triggered by the `thread`
+# TODO(#5592): Investigate and fix this. It can be triggered by the `thread`
 # test suite.
 race:git_filter_list__load_ext

src/config_cache.c

@@ -111,17 +111,18 @@ int git_config__configmap_lookup(int *out, git_config *config, git_configmap_ite
 
 int git_repository__configmap_lookup(int *out, git_repository *repo, git_configmap_item item)
 {
-	*out = repo->configmap_cache[(int)item];
+	*out = (int)(intptr_t)git__load(repo->configmap_cache[(int)item]);
 
 	if (*out == GIT_CONFIGMAP_NOT_CACHED) {
 		int error;
+		int oldval = GIT_CONFIGMAP_NOT_CACHED;
 		git_config *config;
 
 		if ((error = git_repository_config__weakptr(&config, repo)) < 0 ||
 			(error = git_config__configmap_lookup(out, config, item)) < 0)
 			return error;
 
-		repo->configmap_cache[(int)item] = *out;
+		git__compare_and_swap(&repo->configmap_cache[(int)item], &oldval, out);
 	}
 
 	return 0;

src/odb.c

@@ -450,12 +450,18 @@ int git_odb_new(git_odb **out)
 	git_odb *db = git__calloc(1, sizeof(*db));
 	GIT_ERROR_CHECK_ALLOC(db);
 
+	if (git_mutex_init(&db->lock) < 0) {
+		git__free(db);
+		return -1;
+	}
 	if (git_cache_init(&db->own_cache) < 0) {
+		git_mutex_free(&db->lock);
 		git__free(db);
 		return -1;
 	}
 	if (git_vector_init(&db->backends, 4, backend_sort_cmp) < 0) {
 		git_cache_dispose(&db->own_cache);
+		git_mutex_free(&db->lock);
 		git__free(db);
 		return -1;
 	}
@@ -487,13 +493,18 @@ static int add_backend_internal(
 	internal->is_alternate = is_alternate;
 	internal->disk_inode = disk_inode;
 
+	if (git_mutex_lock(&odb->lock) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return -1;
+	}
 	if (git_vector_insert(&odb->backends, internal) < 0) {
+		git_mutex_unlock(&odb->lock);
 		git__free(internal);
 		return -1;
 	}
-
 	git_vector_sort(&odb->backends);
 	internal->backend->odb = odb;
+	git_mutex_unlock(&odb->lock);
 	return 0;
 }
 
@@ -509,8 +520,19 @@ int git_odb_add_alternate(git_odb *odb, git_odb_backend *backend, int priority)
 
 size_t git_odb_num_backends(git_odb *odb)
 {
+	size_t length;
+	bool locked = true;
+
 	GIT_ASSERT_ARG(odb);
-	return odb->backends.length;
+
+	if (git_mutex_lock(&odb->lock) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		locked = false;
+	}
+	length = odb->backends.length;
+	if (locked)
+		git_mutex_unlock(&odb->lock);
+	return length;
 }
 
 static int git_odb__error_unsupported_in_backend(const char *action)
@@ -524,19 +546,28 @@ static int git_odb__error_unsupported_in_backend(const char *action)
 int git_odb_get_backend(git_odb_backend **out, git_odb *odb, size_t pos)
 {
 	backend_internal *internal;
+	int error;
 
 	GIT_ASSERT_ARG(out);
 	GIT_ASSERT_ARG(odb);
 
+
+	if ((error = git_mutex_lock(&odb->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
 	internal = git_vector_get(&odb->backends, pos);
 
-	if (internal && internal->backend) {
-		*out = internal->backend;
-		return 0;
-	}
+	if (!internal || !internal->backend) {
+		git_mutex_unlock(&odb->lock);
 
-	git_error_set(GIT_ERROR_ODB, "no ODB backend loaded at index %" PRIuZ, pos);
-	return GIT_ENOTFOUND;
+		git_error_set(GIT_ERROR_ODB, "no ODB backend loaded at index %" PRIuZ, pos);
+		return GIT_ENOTFOUND;
+	}
+	*out = internal->backend;
+	git_mutex_unlock(&odb->lock);
+
+	return 0;
 }
 
 int git_odb__add_default_backends(
@@ -567,11 +598,18 @@ int git_odb__add_default_backends(
 
 	inode = st.st_ino;
 
+	if (git_mutex_lock(&db->lock) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return -1;
+	}
 	for (i = 0; i < db->backends.length; ++i) {
 		backend_internal *backend = git_vector_get(&db->backends, i);
-		if (backend->disk_inode == inode)
+		if (backend->disk_inode == inode) {
+			git_mutex_unlock(&db->lock);
 			return 0;
+		}
 	}
+	git_mutex_unlock(&db->lock);
 #endif
 
 	/* add the loose object backend */
@@ -687,7 +725,12 @@ int git_odb__set_caps(git_odb *odb, int caps)
 static void odb_free(git_odb *db)
 {
 	size_t i;
+	bool locked = true;
 
+	if (git_mutex_lock(&db->lock) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		locked = false;
+	}
 	for (i = 0; i < db->backends.length; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *backend = internal->backend;
@@ -696,9 +739,12 @@ static void odb_free(git_odb *db)
 
 		git__free(internal);
 	}
+	if (locked)
+		git_mutex_unlock(&db->lock);
 
 	git_vector_free(&db->backends);
 	git_cache_dispose(&db->own_cache);
+	git_mutex_free(&db->lock);
 
 	git__memzero(db, sizeof(*db));
 	git__free(db);
@@ -719,7 +765,12 @@ static int odb_exists_1(
 {
 	size_t i;
 	bool found = false;
+	int error;
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
 	for (i = 0; i < db->backends.length && !found; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -730,6 +781,7 @@ static int odb_exists_1(
 		if (b->exists != NULL)
 			found = (bool)b->exists(b, id);
 	}
+	git_mutex_unlock(&db->lock);
 
 	return (int)found;
 }
@@ -741,7 +793,12 @@ static int odb_freshen_1(
 {
 	size_t i;
 	bool found = false;
+	int error;
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
 	for (i = 0; i < db->backends.length && !found; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -754,6 +811,7 @@ static int odb_freshen_1(
 		else if (b->exists != NULL)
 			found = b->exists(b, id);
 	}
+	git_mutex_unlock(&db->lock);
 
 	return (int)found;
 }
@@ -805,6 +863,11 @@ static int odb_exists_prefix_1(git_oid *out, git_odb *db,
 	int error = GIT_ENOTFOUND, num_found = 0;
 	git_oid last_found = {{0}}, found;
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
+	error = GIT_ENOTFOUND;
 	for (i = 0; i < db->backends.length; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -818,18 +881,23 @@ static int odb_exists_prefix_1(git_oid *out, git_odb *db,
 		error = b->exists_prefix(&found, b, key, len);
 		if (error == GIT_ENOTFOUND || error == GIT_PASSTHROUGH)
 			continue;
-		if (error)
+		if (error) {
+			git_mutex_unlock(&db->lock);
 			return error;
+		}
 
 		/* make sure found item doesn't introduce ambiguity */
 		if (num_found) {
-			if (git_oid__cmp(&last_found, &found))
+			if (git_oid__cmp(&last_found, &found)) {
+				git_mutex_unlock(&db->lock);
 				return git_odb__error_ambiguous("multiple matches for prefix");
+			}
 		} else {
 			git_oid_cpy(&last_found, &found);
 			num_found++;
 		}
 	}
+	git_mutex_unlock(&db->lock);
 
 	if (!num_found)
 		return GIT_ENOTFOUND;
@@ -971,6 +1039,10 @@ static int odb_read_header_1(
 		return 0;
 	}
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
 	for (i = 0; i < db->backends.length; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -992,9 +1064,11 @@ static int odb_read_header_1(
 		case GIT_ENOTFOUND:
 			break;
 		default:
+			git_mutex_unlock(&db->lock);
 			return error;
 		}
 	}
+	git_mutex_unlock(&db->lock);
 
 	return passthrough ? GIT_PASSTHROUGH : GIT_ENOTFOUND;
 }
@@ -1067,6 +1141,10 @@ static int odb_read_1(git_odb_object **out, git_odb *db, const git_oid *id,
 			return error;
 	}
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
 	for (i = 0; i < db->backends.length && !found; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -1079,12 +1157,15 @@ static int odb_read_1(git_odb_object **out, git_odb *db, const git_oid *id,
 			if (error == GIT_PASSTHROUGH || error == GIT_ENOTFOUND)
 				continue;
 
-			if (error < 0)
+			if (error < 0) {
+				git_mutex_unlock(&db->lock);
 				return error;
+			}
 
 			found = true;
 		}
 	}
+	git_mutex_unlock(&db->lock);
 
 	if (!found)
 		return GIT_ENOTFOUND;
@@ -1177,6 +1258,10 @@ static int read_prefix_1(git_odb_object **out, git_odb *db,
 	bool found = false;
 	git_odb_object *object;
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
 	for (i = 0; i < db->backends.length; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -1193,8 +1278,10 @@ static int read_prefix_1(git_odb_object **out, git_odb *db,
 				continue;
 			}
 
-			if (error)
+			if (error) {
+				git_mutex_unlock(&db->lock);
 				goto out;
+			}
 
 			git__free(data);
 			data = raw.data;
@@ -1209,6 +1296,7 @@ static int read_prefix_1(git_odb_object **out, git_odb *db,
 
 				error = git_odb__error_ambiguous(buf.ptr);
 				git_buf_dispose(&buf);
+				git_mutex_unlock(&db->lock);
 				goto out;
 			}
 
@@ -1216,6 +1304,7 @@ static int read_prefix_1(git_odb_object **out, git_odb *db,
 			found = true;
 		}
 	}
+	git_mutex_unlock(&db->lock);
 
 	if (!found)
 		return GIT_ENOTFOUND;
@@ -1283,16 +1372,32 @@ int git_odb_read_prefix(
 int git_odb_foreach(git_odb *db, git_odb_foreach_cb cb, void *payload)
 {
 	unsigned int i;
+	git_vector backends = GIT_VECTOR_INIT;
 	backend_internal *internal;
+	int error = 0;
 
-	git_vector_foreach(&db->backends, i, internal) {
+	/* Make a copy of the backends vector to invoke the callback without holding the lock. */
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		goto cleanup;
+	}
+	error = git_vector_dup(&backends, &db->backends, NULL);
+	git_mutex_unlock(&db->lock);
+
+	if (error < 0)
+		goto cleanup;
+
+	git_vector_foreach(&backends, i, internal) {
 		git_odb_backend *b = internal->backend;
-		int error = b->foreach(b, cb, payload);
+		error = b->foreach(b, cb, payload);
 		if (error != 0)
-			return error;
+			goto cleanup;
 	}
 
-	return 0;
+cleanup:
+	git_vector_free(&backends);
+
+	return error;
 }
 
 int git_odb_write(
@@ -1314,6 +1419,10 @@ int git_odb_write(
 	if (git_odb__freshen(db, oid))
 		return 0;
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
 	for (i = 0, error = GIT_ERROR; i < db->backends.length && error < 0; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -1325,6 +1434,7 @@ int git_odb_write(
 		if (b->write != NULL)
 			error = b->write(b, oid, data, len, type);
 	}
+	git_mutex_unlock(&db->lock);
 
 	if (!error || error == GIT_PASSTHROUGH)
 		return 0;
@@ -1366,6 +1476,11 @@ int git_odb_open_wstream(
 	GIT_ASSERT_ARG(stream);
 	GIT_ASSERT_ARG(db);
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
+	error = GIT_ERROR;
 	for (i = 0; i < db->backends.length && error < 0; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -1382,6 +1497,7 @@ int git_odb_open_wstream(
 			error = init_fake_wstream(stream, b, size, type);
 		}
 	}
+	git_mutex_unlock(&db->lock);
 
 	if (error < 0) {
 		if (error == GIT_PASSTHROUGH)
@@ -1477,6 +1593,11 @@ int git_odb_open_rstream(
 	GIT_ASSERT_ARG(stream);
 	GIT_ASSERT_ARG(db);
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
+	error = GIT_ERROR;
 	for (i = 0; i < db->backends.length && error < 0; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -1486,6 +1607,7 @@ int git_odb_open_rstream(
 			error = b->readstream(stream, len, type, b, oid);
 		}
 	}
+	git_mutex_unlock(&db->lock);
 
 	if (error == GIT_PASSTHROUGH)
 		error = 0;
@@ -1503,6 +1625,11 @@ int git_odb_write_pack(struct git_odb_writepack **out, git_odb *db, git_indexer_
 	GIT_ASSERT_ARG(out);
 	GIT_ASSERT_ARG(db);
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
+	error = GIT_ERROR;
 	for (i = 0; i < db->backends.length && error < 0; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
@@ -1516,6 +1643,7 @@ int git_odb_write_pack(struct git_odb_writepack **out, git_odb *db, git_indexer_
 			error = b->writepack(out, b, db, progress_cb, progress_payload);
 		}
 	}
+	git_mutex_unlock(&db->lock);
 
 	if (error == GIT_PASSTHROUGH)
 		error = 0;
@@ -1547,19 +1675,27 @@ void git_odb_backend_data_free(git_odb_backend *backend, void *data)
 int git_odb_refresh(struct git_odb *db)
 {
 	size_t i;
+	int error;
 
 	GIT_ASSERT_ARG(db);
 
+	if ((error = git_mutex_lock(&db->lock)) < 0) {
+		git_error_set(GIT_ERROR_ODB, "failed to acquire the odb lock");
+		return error;
+	}
 	for (i = 0; i < db->backends.length; ++i) {
 		backend_internal *internal = git_vector_get(&db->backends, i);
 		git_odb_backend *b = internal->backend;
 
 		if (b->refresh != NULL) {
 			int error = b->refresh(b);
-			if (error < 0)
+			if (error < 0) {
+				git_mutex_unlock(&db->lock);
 				return error;
+			}
 		}
 	}
+	git_mutex_unlock(&db->lock);
 
 	return 0;
 }

src/odb.h

@@ -40,6 +40,7 @@ struct git_odb_object {
 /* EXPORT */
 struct git_odb {
 	git_refcount rc;
+	git_mutex lock;  /* protects backends */
 	git_vector backends;
 	git_cache own_cache;
 	unsigned int do_fsync :1;

src/pack.c

@@ -12,6 +12,7 @@
 #include "mwindow.h"
 #include "odb.h"
 #include "oid.h"
+#include "oidarray.h"
 
 /* Option to bypass checking existence of '.keep' files */
 bool git_disable_pack_keep_file_checks = false;
@@ -195,7 +196,8 @@ static void pack_index_free(struct git_pack_file *p)
 	}
 }
 
-static int pack_index_check(const char *path, struct git_pack_file *p)
+/* Run with the packfile lock held */
+static int pack_index_check_locked(const char *path, struct git_pack_file *p)
 {
 	struct git_pack_idx_header *hdr;
 	uint32_t version, nr, i, *index;
@@ -301,7 +303,8 @@ static int pack_index_check(const char *path, struct git_pack_file *p)
 	return 0;
 }
 
-static int pack_index_open(struct git_pack_file *p)
+/* Run with the packfile lock held */
+static int pack_index_open_locked(struct git_pack_file *p)
 {
 	int error = 0;
 	size_t name_len;
@@ -324,18 +327,11 @@ static int pack_index_open(struct git_pack_file *p)
 		return -1;
 	}
 
-	if ((error = git_mutex_lock(&p->lock)) < 0) {
-		git_buf_dispose(&idx_name);
-		return error;
-	}
-
 	if (p->index_version == -1)
-		error = pack_index_check(idx_name.ptr, p);
+		error = pack_index_check_locked(idx_name.ptr, p);
 
 	git_buf_dispose(&idx_name);
 
-	git_mutex_unlock(&p->lock);
-
 	return error;
 }
 
@@ -1015,13 +1011,14 @@ static int packfile_open(struct git_pack_file *p)
 	git_oid sha1;
 	unsigned char *idx_sha1;
 
-	if (p->index_version == -1 && pack_index_open(p) < 0)
-		return git_odb__error_notfound("failed to open packfile", NULL, 0);
-
-	/* if mwf opened by another thread, return now */
 	if (git_mutex_lock(&p->lock) < 0)
 		return packfile_error("failed to get lock for open");
 
+	if (pack_index_open_locked(p) < 0) {
+		git_mutex_unlock(&p->lock);
+		return git_odb__error_notfound("failed to open packfile", NULL, 0);
+	}
+
 	if (p->mwf.fd >= 0) {
 		git_mutex_unlock(&p->lock);
 		return 0;
@@ -1210,32 +1207,40 @@ int git_pack_foreach_entry(
 	git_odb_foreach_cb cb,
 	void *data)
 {
-	const unsigned char *index = p->index_map.data, *current;
+	const unsigned char *index, *current;
 	uint32_t i;
 	int error = 0;
+	git_array_oid_t oids = GIT_ARRAY_INIT;
+	git_oid *oid;
 
-	if (index == NULL) {
-		if ((error = pack_index_open(p)) < 0)
-			return error;
+	if (git_mutex_lock(&p->lock) < 0)
+		return packfile_error("failed to get lock for git_pack_foreach_entry");
 
-		GIT_ASSERT(p->index_map.data);
-		index = p->index_map.data;
+	if ((error = pack_index_open_locked(p)) < 0) {
+		git_mutex_unlock(&p->lock);
+		return error;
 	}
 
-	if (p->index_version > 1) {
+	GIT_ASSERT(p->index_map.data);
+	index = p->index_map.data;
+
+	if (p->index_version > 1)
 		index += 8;
-	}
 
 	index += 4 * 256;
 
 	if (p->oids == NULL) {
 		git_vector offsets, oids;
 
-		if ((error = git_vector_init(&oids, p->num_objects, NULL)))
+		if ((error = git_vector_init(&oids, p->num_objects, NULL))) {
+			git_mutex_unlock(&p->lock);
 			return error;
+		}
 
-		if ((error = git_vector_init(&offsets, p->num_objects, git__memcmp4)))
+		if ((error = git_vector_init(&offsets, p->num_objects, git__memcmp4))) {
+			git_mutex_unlock(&p->lock);
 			return error;
+		}
 
 		if (p->index_version > 1) {
 			const unsigned char *off = index + 24 * p->num_objects;
@@ -1256,10 +1261,33 @@ int git_pack_foreach_entry(
 		p->oids = (git_oid **)git_vector_detach(NULL, NULL, &oids);
 	}
 
-	for (i = 0; i < p->num_objects; i++)
-		if ((error = cb(p->oids[i], data)) != 0)
-			return git_error_set_after_callback(error);
+	/* We need to copy the OIDs to another array before we relinquish the lock to avoid races. */
+	git_array_init_to_size(oids, p->num_objects);
+	if (!oids.ptr) {
+		git_mutex_unlock(&p->lock);
+		git_array_clear(oids);
+		GIT_ERROR_CHECK_ARRAY(oids);
+	}
+	for (i = 0; i < p->num_objects; i++) {
+		oid = git_array_alloc(oids);
+		if (!oid) {
+			git_mutex_unlock(&p->lock);
+			git_array_clear(oids);
+			GIT_ERROR_CHECK_ALLOC(oid);
+		}
+		git_oid_cpy(oid, p->oids[i]);
+	}
 
+	git_mutex_unlock(&p->lock);
+
+	git_array_foreach(oids, i, oid) {
+		if ((error = cb(oid, data)) != 0) {
+			git_error_set_after_callback(error);
+			break;
+		}
+	}
+
+	git_array_clear(oids);
 	return error;
 }
 
@@ -1297,18 +1325,17 @@ static int pack_entry_find_offset(
 	int pos, found = 0;
 	off64_t offset;
 	const unsigned char *current = 0;
+	int error = 0;
 
 	*offset_out = 0;
 
-	if (p->index_version == -1) {
-		int error;
+	if (git_mutex_lock(&p->lock) < 0)
+		return packfile_error("failed to get lock for pack_entry_find_offset");
 
-		if ((error = pack_index_open(p)) < 0)
-			return error;
-
-		GIT_ASSERT(p->index_map.data);
-	}
+	if ((error = pack_index_open_locked(p)) < 0)
+		goto cleanup;
 
+	GIT_ASSERT(p->index_map.data);
 	index = p->index_map.data;
 	level1_ofs = p->index_map.data;
 
@@ -1360,14 +1387,19 @@ static int pack_entry_find_offset(
 		}
 	}
 
-	if (!found)
-		return git_odb__error_notfound("failed to find offset for pack entry", short_oid, len);
-	if (found > 1)
-		return git_odb__error_ambiguous("found multiple offsets for pack entry");
+	if (!found) {
+		error = git_odb__error_notfound("failed to find offset for pack entry", short_oid, len);
+		goto cleanup;
+	}
+	if (found > 1) {
+		error = git_odb__error_ambiguous("found multiple offsets for pack entry");
+		goto cleanup;
+	}
 
 	if ((offset = nth_packed_object_offset(p, pos)) < 0) {
 		git_error_set(GIT_ERROR_ODB, "packfile index is corrupt");
-		return -1;
+		error = -1;
+		goto cleanup;
 	}
 
 	*offset_out = offset;
@@ -1382,7 +1414,9 @@ static int pack_entry_find_offset(
 	}
 #endif
 
-	return 0;
+cleanup:
+	git_mutex_unlock(&p->lock);
+	return error;
 }
 
 int git_pack_entry_find(

src/repository.c

@@ -1107,7 +1107,8 @@ int git_repository_odb__weakptr(git_odb **out, git_repository *repo)
 	GIT_ASSERT_ARG(repo);
 	GIT_ASSERT_ARG(out);
 
-	if (repo->_odb == NULL) {
+	*out = git__load(repo->_odb);
+	if (*out == NULL) {
 		git_buf odb_path = GIT_BUF_INIT;
 		git_odb *odb;
 
@@ -1131,9 +1132,9 @@ int git_repository_odb__weakptr(git_odb **out, git_repository *repo)
 		}
 
 		git_buf_dispose(&odb_path);
+		*out = git__load(repo->_odb);
 	}
 
-	*out = repo->_odb;
 	return error;
 }