From 18c03b13d1a53282e69160fa71a7195a11e84392 Mon Sep 17 00:00:00 2001 From: Rickard Green Date: Thu, 7 Aug 2014 22:02:25 +0200 Subject: Fix emigrate bug in erts_port_task_schedule() While current run-queue lock is unlocked in the call to erts_check_emigration_need() from erts_port_task_schedule() the port can be migrated to another run-queue by another thread. The code in erts_port_task_schedule() needs to check if this has occurred when returning from erts_check_emigration_need(), and if so respect the migration decision. When this was not done, the thread calling erts_port_task_schedule() held the wrong run-queue lock which caused invalid updates of the port task queue. This bug was automatically fixed by the rewrites in the branch rickard/r16b/port-optimizations-fixes/OTP-10336 (commit 56cef897ca3ad2377e34a6ea5800a54a28cbeb6e) introduced in erts-5.10 and do not effect erts versions after that. --- erts/emulator/beam/erl_port_task.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-) (limited to 'erts') diff --git a/erts/emulator/beam/erl_port_task.c b/erts/emulator/beam/erl_port_task.c index 3dc7c14faf..11027dda7a 100644 --- a/erts/emulator/beam/erl_port_task.c +++ b/erts/emulator/beam/erl_port_task.c @@ -576,8 +576,20 @@ erts_port_task_schedule(Eterm id, if (!pp->sched.taskq && !pp->sched.exe_taskq) { #ifdef ERTS_SMP ErtsRunQueue *xrunq = erts_check_emigration_need(runq, ERTS_PORT_PRIO_LEVEL); - if (xrunq) { - /* Port emigrated ... */ + ERTS_SMP_LC_ASSERT(runq != xrunq); + if (runq != (ErtsRunQueue *) erts_smp_atomic_read_nob(&pp->run_queue)) { + /* + * Someone else migrated this port while we had the run-queue + * lock on runq unlocked in erts_check_emigration_need(). Respect + * that migration decision... + */ + erts_smp_runq_unlock(runq); + if (xrunq) + erts_smp_runq_unlock(xrunq); + runq = erts_port_runq(pp); + } + else if (xrunq) { + /* Emigrate port... */ erts_smp_atomic_set_nob(&pp->run_queue, (erts_aint_t) xrunq); erts_smp_runq_unlock(runq); runq = xrunq; @@ -929,6 +941,8 @@ erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp) #ifdef ERTS_SMP xrunq = erts_check_emigration_need(runq, ERTS_PORT_PRIO_LEVEL); + ERTS_SMP_LC_ASSERT(runq != xrunq); + ERTS_SMP_LC_ASSERT(runq == (ErtsRunQueue *) erts_smp_atomic_read_nob(&pp->run_queue)); if (!xrunq) { #endif enqueue_port(runq, pp); @@ -938,7 +952,7 @@ erts_port_task_execute(ErtsRunQueue *runq, Port **curr_port_pp) #ifdef ERTS_SMP } else { - /* Port emigrated ... */ + /* Emigrate port... */ erts_smp_atomic_set_nob(&pp->run_queue, (erts_aint_t) xrunq); enqueue_port(xrunq, pp); ASSERT(pp->sched.exe_taskq); -- cgit v1.2.3