[PATCH] pack-objects.c: Initialize read mutex in cmd_pack_objects

[Patrick Hogg <phogg@xxxxxxxxxxxx>]

ac77d0c37 ("pack-objects: shrink size field in struct object_entry",
2018-04-14) added an extra usage of read_lock/read_unlock in the newly
introduced oe_get_size_slow for thread safety in parallel calls to
try_delta(). Unfortunately oe_get_size_slow is also used in serial
code, some of which is called before the first invocation of
ll_find_deltas. As such the read mutex is not guaranteed to be
initialized.

Resolve this by splitting off the read mutex initialization from
init_threaded_search. Instead initialize (and clean up) the read
mutex in cmd_pack_objects.

Signed-off-by: Patrick Hogg <phogg@xxxxxxxxxxxx>
---
 builtin/pack-objects.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 411aefd68..9084bef02 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -2381,22 +2381,30 @@ static pthread_cond_t progress_cond;
  */
 static void init_threaded_search(void)
 {
-	init_recursive_mutex(&read_mutex);
 	pthread_mutex_init(&cache_mutex, NULL);
 	pthread_mutex_init(&progress_mutex, NULL);
 	pthread_cond_init(&progress_cond, NULL);
 	old_try_to_free_routine = set_try_to_free_routine(try_to_free_from_threads);
 }
 
+static void init_read_mutex(void)
+{
+	init_recursive_mutex(&read_mutex);
+}
+
 static void cleanup_threaded_search(void)
 {
 	set_try_to_free_routine(old_try_to_free_routine);
 	pthread_cond_destroy(&progress_cond);
-	pthread_mutex_destroy(&read_mutex);
 	pthread_mutex_destroy(&cache_mutex);
 	pthread_mutex_destroy(&progress_mutex);
 }
 
+static void cleanup_read_mutex(void)
+{
+	pthread_mutex_destroy(&read_mutex);
+}
+
 static void *threaded_find_deltas(void *arg)
 {
 	struct thread_params *me = arg;
@@ -3319,6 +3327,8 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 		OPT_END(),
 	};
 
+	init_read_mutex();
+
 	if (DFS_NUM_STATES > (1 << OE_DFS_STATE_BITS))
 		BUG("too many dfs states, increase OE_DFS_STATE_BITS");
 
@@ -3495,5 +3505,7 @@ int cmd_pack_objects(int argc, const char **argv, const char *prefix)
 			   _("Total %"PRIu32" (delta %"PRIu32"),"
 			     " reused %"PRIu32" (delta %"PRIu32")"),
 			   written, written_delta, reused, reused_delta);
+
+	cleanup_read_mutex();
 	return 0;
 }
-- 
2.20.1.windows.1