Re: [PATCH] rcu/tree: consider time a VM was suspended

[Sergey Senozhatsky]

On (21/05/20 17:14), Paul E. McKenney wrote:
> > On a side note.
> > 
> > I wish we didn't have to put kvm_check_and_clear_guest_paused() all
> > over the place.
> > 
> > We do load jiffies at the start of check_cpu_stall(). So, in theory,
> > we can just use that captured jiffies (which can become obsolete but
> > so will grace period timestamps) value and never read current system
> > jiffies because they can jump way forward. IOW
> > 
> > 	jn = j + 3 * rcu_jiffies_till_stall_check() + 3;
> > 
> > instead of
> > 
> > 	jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
> > 
> > Then we probably can remove kvm_check_and_clear_guest_paused().
> > 
> > But that "don't load current jiffies" is rather fragile.
> > 
> > kvm_check_and_clear_guest_paused() is not pretty, but at least it's
> > explicit.
> 
> If this works for you, I am very much in favor!

Oh, no. Sorry for the noise. This is racy and won't work.