UCM/BISTRO: Increase grace time to reduce patch race

src/ucm/api/ucm.h

@@ -219,6 +219,8 @@ typedef struct ucm_global_config {
     int                  dlopen_process_rpath;        /* Process RPATH section in dlopen hook */
     int                  module_unload_prevent_mode;  /* Module unload prevention mode */
     int                  bistro_force_far_jump;       /* Force far jump with bistro patching */
+    double               bistro_grace_duration;       /* Grace duration for bistro patching 
+                                                       * in seconds */
 } ucm_global_config_t;
 
 

src/ucm/bistro/bistro.c

@@ -70,8 +70,7 @@ void ucm_bistro_modify_code(void *dst, const ucm_bistro_lock_t *bytes)
 ucs_status_t
 ucm_bistro_apply_patch_atomic(void *dst, const void *patch, size_t len)
 {
-    size_t skip           = sizeof(ucm_bistro_lock_t);
-    double grace_duration = 5e-3;
+    size_t skip = sizeof(ucm_bistro_lock_t);
     double deadline;
     ucs_status_t status;
 
@@ -84,7 +83,7 @@ ucm_bistro_apply_patch_atomic(void *dst, const void *patch, size_t len)
     ucm_bistro_patch_lock(dst);
     ucs_clear_cache(dst, UCS_PTR_BYTE_OFFSET(dst, len));
 
-    deadline = ucm_get_time() + grace_duration;
+    deadline = ucm_get_time() + ucm_global_opts.bistro_grace_duration;
     while (ucm_get_time() < deadline) {
         sched_yield();
     }

src/ucs/config/ucm_opts.c

@@ -112,6 +112,13 @@ static ucs_config_field_t ucm_global_config_table[] = {
    ucs_offsetof(ucm_global_config_t, bistro_force_far_jump),
    UCS_CONFIG_TYPE_BOOL},
 
+  {"BISTRO_GRACE_DURATION", "50ms",
+   "Grace period duration to wait for existing code flows to complete when\n"
+   "applying bistro patches. This allows threads currently executing patched\n"
+   "code to finish before the patch is applied.",
+   ucs_offsetof(ucm_global_config_t, bistro_grace_duration),
+   UCS_CONFIG_TYPE_TIME},
+
   {NULL}
 };