On Thu, Sep 24, 2020 at 01:25:06PM -0400, Mathieu Desnoyers wrote: > diff --git a/kernel/exit.c b/kernel/exit.c > index 733e80f334e7..0767a2dbf245 100644 > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -475,7 +475,19 @@ static void exit_mm(void) > BUG_ON(mm != current->active_mm); > /* more a memory barrier than a real lock */ > task_lock(current); > + /* > + * When a thread stops operating on an address space, the loop > + * in membarrier_private_expedited() may not observe that > + * tsk->mm, and the loop in membarrier_global_expedited() may > + * not observe a MEMBARRIER_STATE_GLOBAL_EXPEDITED > + * rq->membarrier_state, so those would not issue an IPI. > + * Membarrier requires a memory barrier after accessing > + * user-space memory, before clearing tsk->mm or the > + * rq->membarrier_state. > + */ > + smp_mb__after_spinlock(); > current->mm = NULL; > + membarrier_update_current_mm(NULL); > mmap_read_unlock(mm); > enter_lazy_tlb(mm, current); > task_unlock(current); This site seems to be lacking in IRQ disabling. As proposed it will explode on RT. Something like so to match kthread_unuse_mm(). --- a/kernel/exit.c +++ b/kernel/exit.c @@ -486,11 +486,13 @@ static void exit_mm(void) * rq->membarrier_state. */ smp_mb__after_spinlock(); + local_irq_disable() current->mm = NULL; membarrier_update_current_mm(NULL); - mmap_read_unlock(mm); enter_lazy_tlb(mm, current); + local_irq_enable(); task_unlock(current); + mmap_read_unlock(mm); mm_update_next_owner(mm); mmput(mm); if (test_thread_flag(TIF_MEMDIE))
