----- On Sep 9, 2019, at 7:00 AM, Oleg Nesterov [email protected] wrote: > On 09/08, Mathieu Desnoyers wrote: >> >> +static void sync_runqueues_membarrier_state(struct mm_struct *mm) >> +{ >> + int membarrier_state = atomic_read(&mm->membarrier_state); >> + bool fallback = false; >> + cpumask_var_t tmpmask; >> + int cpu; >> + >> + if (atomic_read(&mm->mm_users) == 1 || num_online_cpus() == 1) { >> + WRITE_ONCE(this_rq()->membarrier_state, membarrier_state); > > This doesn't look safe, this caller can migrate to another CPU after > it calculates the per-cpu ptr. > > I think you need do disable preemption or simply use this_cpu_write().
Good point! I'll use this_cpu_write() there and within membarrier_exec_mmap(), which seems to be affected by the same problem. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
