erts: release dirty runqueue lock before entering endless loop when BEAM is shutting down

This patch fixes a problem happening when BEAM is shutting down. It is possible for a dirty scheduler to take the lock, and keep it, when the system is shutting down. It may also happen that a normal scheduler decides to schedule some dirty job (example is major garbage collection that results in migrating the process into dirty CPU queue), and hangs trying to take the lock that will never be released.

To fix the problem, either release the lock before entering endless wait loop, or reverse the order in which schedulers are stopped. Either fix works, and, of course, it works even better to apply both.

1 files changed, 2 insertions, 1 deletions

diff --git a/erts/emulator/beam/erl_process.c b/erts/emulator/beam/erl_process.c
index 6779d9f218..5b6885f18e 100644
--- a/erts/emulator/beam/erl_process.c
+++ b/erts/emulator/beam/erl_process.c
@@ -10550,6 +10550,7 @@ Process *erts_schedule(ErtsSchedulerData *esdp, Process *p, int calls)
 
 	if (!is_normal_sched & !!(flags & ERTS_RUNQ_FLG_HALTING)) {
 	    /* Wait for emulator to terminate... */
+	    erts_runq_unlock(rq);
 	    while (1)
 		erts_milli_sleep(1000*1000);
 	}
@@ -14593,12 +14594,12 @@ void erts_halt(int code)
     if (-1 == erts_smp_atomic32_cmpxchg_acqb(&erts_halt_progress,
 					     erts_no_schedulers,
 					     -1)) {
+        notify_reap_ports_relb();
 #ifdef ERTS_DIRTY_SCHEDULERS
         ERTS_RUNQ_FLGS_SET(ERTS_DIRTY_CPU_RUNQ, ERTS_RUNQ_FLG_HALTING);
         ERTS_RUNQ_FLGS_SET(ERTS_DIRTY_IO_RUNQ, ERTS_RUNQ_FLG_HALTING);
 #endif
 	erts_halt_code = code;
-	notify_reap_ports_relb();
     }
 }