Hi Frederic,
On 9/4/2022 5:01 PM, Frederic Weisbecker wrote:
> On Sat, Sep 03, 2022 at 10:00:29PM +0000, Joel Fernandes wrote:
>> On Fri, Sep 02, 2022 at 05:21:32PM +0200, Frederic Weisbecker wrote:
>> +
>> + raw_spin_lock_irqsave(&my_rdp->nocb_gp_lock, flags);
>
> This is locking during the whole group iteration potentially contending call_rcu(),
> idle loop, resume to userspace on all rdp in the group...
>
> How about not overwriting timers instead and only set the RCU_NOCB_WAKE_LAZY
> timer when it is previously in RCU_NOCB_WAKE_NOT state? After all if the timer is armed,
> it's because we have regular callbacks queued and thus we don't need to wait
> before processing the lazy callbacks since we are going to start a grace period
> anyway.
>
> Thanks.
I like your idea better. I think it will work well to resolve the race you
described.
Thanks!
- Joel
>
>
>> list_for_each_entry_rcu(rdp, &my_rdp->nocb_head_rdp, nocb_entry_rdp, 1) {
>> bool needwake_state = false;
>> bool flush_bypass = false;
>> @@ -855,14 +870,15 @@ static void nocb_gp_wait(struct rcu_data *my_rdp)
>> // If bypass list only has lazy CBs. Add a deferred
>> // lazy wake up.
>> if (lazy && !bypass) {
>> - wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_LAZY,
>> + wake_nocb_gp_defer_locked(my_rdp, RCU_NOCB_WAKE_LAZY,
>> TPS("WakeLazyIsDeferred"));
>> // Otherwise add a deferred bypass wake up.
>> } else if (bypass) {
>> - wake_nocb_gp_defer(my_rdp, RCU_NOCB_WAKE_BYPASS,
>> + wake_nocb_gp_defer_locked(my_rdp, RCU_NOCB_WAKE_BYPASS,
>> TPS("WakeBypassIsDeferred"));
>> }
>> }
>> + raw_spin_unlock_irqrestore(&my_rdp->nocb_gp_lock, flags);
>>
>> if (rcu_nocb_poll) {
>> /* Polling, so trace if first poll in the series. */
>> --
>> 2.37.2.789.g6183377224-goog
>>
