[LKP] Re: [mm] 4e2c82a409: ltp.overcommit_memory01.fail

On Mon, Jul 06, 2020 at 06:34:34AM -0700, Andi Kleen wrote: > > ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos); > > - if (ret == 0 && write) > > + if (ret == 0 && write) { > > + if (sysctl_overcommit_memory == OVERCOMMIT_NEVER) > > + schedule_on_each_cpu(sync_overcommit_as); > > The schedule_on_each_cpu is not atomic, so the problem could still happen > in that window. > > I think it may be ok if it eventually resolves, but certainly needs > a comment explaining it. Can you do some stress testing toggling the > policy all the time on different CPUs and running the test on > other CPUs and see if the test fails? For the raw test case reported by 0day, this patch passed in 200 times run. And I will read the ltp code and try stress testing it as you suggested. > The other alternative would be to define some intermediate state > for the sysctl variable and only switch to never once the schedule_on_each_cpu > returned. But that's more complexity. One thought I had is to put this schedule_on_each_cpu() before the proc_dointvec_minmax() to do the sync before sysctl_overcommit_memory is really changed. But the window still exists, as the batch is still the larger one.