Re: [PATCH] rcu: Use an intermediate irq_work to start process_srcu()

[Joel Fernandes <joelagnelf@nvidia.com>]

On 3/20/2026 2:14 PM, Boqun Feng wrote:
> Since commit c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms
> of SRCU-fast") we switched to SRCU in BPF. However as BPF instrument can
> happen basically everywhere (including where a scheduler lock is held),
> call_srcu() now needs to avoid acquiring scheduler lock because
> otherwise it could cause deadlock [1]. Fix this by following what the
> previous RCU Tasks Trace did: using an irq_work to delay the queuing of
> the work to start process_srcu().
> 
> [boqun: Apply Joel's feedback]
> 
> Reported-by: Andrea Righi <arighi@nvidia.com>
> Closes: https://lore.kernel.org/all/abjzvz_tL_siV17s@gpd4/
> Fixes: commit c27cea4416a3 ("rcu: Re-implement RCU Tasks Trace in terms of SRCU-fast")
> Link: https://lore.kernel.org/rcu/3c4c5a29-24ea-492d-aeee-e0d9605b4183@nvidia.com/ [1]
> Suggested-by: Zqiang <qiang.zhang@linux.dev>
> Signed-off-by: Boqun Feng <boqun@kernel.org>
> ---
> @Zqiang, I put your name as Suggested-by because you proposed the same
> idea, let me know if you rather not have it.
> 
> @Joel, I did two updates (including your test feedback, other one is
> call irq_work_sync() when we clean the srcu_struct), please give it a
> try.

Thanks Boqun, I applied it for testing further. It would be good if Andrea and
Kumar can try this patch as well to confirm that the BPF issues are gone.

thanks,

--
Joel Fernandes