On Fri, Aug 25, 2023 at 10:28:37AM +0800, Z qiang wrote: > > > > On Thu, Aug 24, 2023 at 04:42:06PM +0800, Zqiang wrote: > > > Currently, the maxcpu is set by traversing online CPUs, however, if > > > the rcutorture.onoff_holdoff is set zero and onoff_interval is set > > > non-zero, and the some CPUs with larger cpuid has been offline before > > > setting maxcpu, for these CPUs, even if they are online again, also > > > cannot be offload or deoffload. > > > > > > This commit therefore use for_each_possible_cpu() instead of > > > for_each_online_cpu() in rcu_nocb_toggle(). > > > > > > Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx> > > > --- > > > kernel/rcu/rcutorture.c | 2 +- > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c > > > index a58372bdf0c1..b75d0fe558ce 100644 > > > --- a/kernel/rcu/rcutorture.c > > > +++ b/kernel/rcu/rcutorture.c > > > @@ -2131,7 +2131,7 @@ static int rcu_nocb_toggle(void *arg) > > > VERBOSE_TOROUT_STRING("rcu_nocb_toggle task started"); > > > while (!rcu_inkernel_boot_has_ended()) > > > schedule_timeout_interruptible(HZ / 10); > > > - for_each_online_cpu(cpu) > > > + for_each_possible_cpu(cpu) > > > > Last I checked, bad things could happen if the code attempted to > > nocb_toggle a CPU that had not yet come online. Has that changed? > > For example, there are 8 online CPUs in the system, before we traversing online > CPUs and set maxcpu, CPU7 has been offline, this causes us to miss nocb_toggle > for CPU7(maxcpu=6) > > Even though we still use for_each_online_cpu(), the things described > above also happen. before we toggle the CPU, this CPU has been offline. Suppose we have a system whose possible CPUs are 0, 1, 2, and 3. However, only 0 and 1 are present in this system, and until some manual action is taken, only 0 and 1 will ever be online. (Yes, this really can happen!) In that state, won't toggling CPU 2 and 3 result in failures? Thanx, Paul > Thanks > Zqiang > > > > > > Thanx, Paul > > > > > maxcpu = cpu; > > > WARN_ON(maxcpu < 0); > > > if (toggle_interval > ULONG_MAX) > > > -- > > > 2.17.1 > > >