On 1/5/2026 10:31 AM, Steven Rostedt wrote:
> On Fri, 2 Jan 2026 19:23:30 -0500
> Joel Fernandes <[email protected]> wrote:
>
>> Add a WARN_ON_ONCE to detect this invariant violation. If this
>> warning ever fires, it indicates a bug where a task was added to
>> a blocked list without properly setting the blocked flag first.
>>
>> Signed-off-by: Joel Fernandes <[email protected]>
>> ---
>> kernel/rcu/tree_plugin.h | 1 +
>> 1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
>> index dbe2d02be824..73ba5f4a968d 100644
>> --- a/kernel/rcu/tree_plugin.h
>> +++ b/kernel/rcu/tree_plugin.h
>> @@ -846,6 +846,7 @@ void exit_rcu(void)
>> if (unlikely(!list_empty(¤t->rcu_node_entry))) {
>> rcu_preempt_depth_set(1);
>> barrier();
>> + WARN_ON_ONCE(!t->rcu_read_unlock_special.b.blocked);
>> WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
Right, so it is ever not set then we are trying to "right" a "wrong", so..
>
> If we warn when it is not set, could we just remove setting it?
> Or do:
>
> if (WARN_ON_ONCE(!t->rcu_read_unlock_special.b.blocked))
> WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true);
.. we could just do this. I'll apply the suggestion, thanks!
- Joel
