[PATCH] rcu: add deprecation notice about limit on defer queue element size

[Thomas Monjalon]

10/07/2025 16:37, Andre Muezerie:
> On Tue, Jul 01, 2025 at 04:17:20PM +0200, Thomas Monjalon wrote:
> > 23/05/2025 01:37, Andre Muezerie:
> > > The functions rte_rcu_qsbr_dq_create and rte_rcu_qsbr_dq_reclaim establish
> > > no limit on the size of each element in the defer queue.
> > 
> > Very good, we need more unlimited API in DPDK.
> > 
> > > With DPDK 25.11 a hard limit will be set (``RTE_QSBR_ESIZE_MAX``).
> > 
> > I think it is a step in the wrong direction.
> > I prefer having no limit.
> > 
> > > This will allow fixed C arrays to be used in the functions' implementations,
> > > avoiding VLAs and use of alloca().
> > 
> > I don't understand this justification.
> > Why trying to remove the 2 alloca() in the lib RCU?
> > 
> 
> Only because other developer expressed concerns that using alloca() allows
> ill-intended callers to cause a stack overflow.
> I personally also prefer to have no hardcoded limits.

Yes I vote for keeping alloca().