Take profile lock after suspending thread

Author: tkf

src/signals-unix.c

@@ -750,7 +750,6 @@ static void *signal_listener(void *arg)
         // sample each thread, round-robin style in reverse order
         // (so that thread zero gets notified last)
         if (critical || profile) {
-            jl_lock_profile();
             if (!critical)
                 jl_shuffle_int_array_inplace(profile_round_robin_thread_order, jl_n_threads, &profile_cong_rng_seed);
             for (int idx = jl_n_threads; idx-- > 0; ) {
@@ -759,6 +758,10 @@ static void *signal_listener(void *arg)
                 // notify thread to stop
                 jl_thread_suspend_and_get_state(i, &signal_context);
 
+                // Taking profile lock after to avoid deadlock in case the i-th thread is
+                // trying to take the lock when signalled.
+                jl_lock_profile();
+
                 // do backtrace on thread contexts for critical signals
                 // this part must be signal-handler safe
                 if (critical) {
@@ -810,10 +813,11 @@ static void *signal_listener(void *arg)
                     }
                 }
 
+                jl_unlock_profile();
+
                 // notify thread to resume
                 jl_thread_resume(i, sig);
             }
-            jl_unlock_profile();
         }
 #ifndef HAVE_MACH
         if (profile && running) {