On 08/01, Thomas Gleixner wrote: > > On Thu, 1 Aug 2019, Oleg Nesterov wrote: > > On 08/01, Thomas Gleixner wrote: > > > > > > @@ -8172,6 +8174,10 @@ static int vcpu_run(struct kvm_vcpu *vcp > > > ++vcpu->stat.signal_exits; > > > break; > > > } > > > + > > > + if (notify_resume_pending()) > > > + tracehook_handle_notify_resume(); > > > > shouldn't you drop kvm->srcu before tracehook_handle_notify_resume() ? > > > > I don't understand this code at all, but vcpu_run() does this even before > > cond_resched(). > > Yeah, I noticed that it's dropped around cond_resched(). > > My understanding is that for voluntary giving up the CPU via cond_resched() > it needs to be dropped. I am not sure it really needs, but this doesn't matter. tracehook_handle_notify_resume() can do "anything", say it can run the works queued by systemtap. I don't think it should delay synchronize_srcu(). And may be this is simply unsafe, even if I don't think a task_work can ever call synchronize_srcu(kvm->srcu) directly. Oleg.
