On 08/07/2015 08:42 AM, Daniel Wagner wrote:
> On 08/05/2015 03:30 PM, Daniel Wagner wrote:
>> My test system didn't crash or showed any obvious defects, so I
>> decided to apply some benchmarks utilizing mmtests. I have picked some
>
> As it turns out, this is not really true. I forgot to enable lockdep:
[...]
> If I decoded this correctly the call to rcu_future_gp_cleanup() is
> supposed to run with IRQs disabled. swake_up_all() though will reenable the
> IRQs:
>
> rcu_gp_cleanup()
> rcu_for_each_node_breadth_first(rsp, rnp) {
> raw_spin_lock_irq(&rnp->lock);
>
> nocb += rcu_future_gp_cleanup(rsp, rnp);
> raw_spin_unlock_irq(&rnp->lock);
> }
>
> rcu_future_gp_cleanup()
> rcu_nocb_gp_cleanup()
> swake_up_all()
>
>
> With IRQs enabled again and we end up in rcu_process_callbacks
> under SOFTIRQ. rcu_process_callbacks aquires the RCU lock again.
>
> Not sure what to do here.
Not really knowing if this is okay but I think the call to
rcu_nocb_gp_cleanup() inside rcu_future_gp_cleanup() doesn't need to be
protected by rnp->lock. At least lockdep and rcutorture is still happy.
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d424378..9411fc3 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1569,7 +1569,6 @@ static int rcu_future_gp_cleanup(struct rcu_state
*rsp, struct rcu_node *rnp)
int needmore;
struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
- rcu_nocb_gp_cleanup(rsp, rnp);
rnp->need_future_gp[c & 0x1] = 0;
needmore = rnp->need_future_gp[(c + 1) & 0x1];
trace_rcu_future_gp(rnp, rdp, c,
@@ -1992,6 +1991,7 @@ static void rcu_gp_cleanup(struct rcu_state *rsp)
/* smp_mb() provided by prior unlock-lock pair. */
nocb += rcu_future_gp_cleanup(rsp, rnp);
raw_spin_unlock_irq(&rnp->lock);
+ rcu_nocb_gp_cleanup(rsp, rnp);
cond_resched_rcu_qs();
WRITE_ONCE(rsp->gp_activity, jiffies);
rcu_gp_slow(rsp, gp_cleanup_delay);
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