[v3] accel: Preparatory cleanups for split-accel

[PATCH v3 56/68] accel/tcg: Unregister the RCU before exiting RR thread

Philippe Mathieu-Daudé posted 68 patches 7 months, 1 week ago

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Maintainers: Richard Henderson <richard.henderson@linaro.org>, Paolo Bonzini <pbonzini@redhat.com>, Cameron Esfahani <dirty@apple.com>, Roman Bolshakov <rbolshakov@ddn.com>, Phil Dennis-Jordan <phil@philjordan.eu>, Fabiano Rosas <farosas@suse.de>, Laurent Vivier <lvivier@redhat.com>, Stefano Stabellini <sstabellini@kernel.org>, Anthony PERARD <anthony@xenproject.org>, Paul Durrant <paul@xen.org>, "Edgar E. Iglesias" <edgar.iglesias@gmail.com>, Warner Losh <imp@bsdimp.com>, Kyle Evans <kevans@freebsd.org>, "Alex Bennée" <alex.bennee@linaro.org>, "Philippe Mathieu-Daudé" <philmd@linaro.org>, "Dr. David Alan Gilbert" <dave@treblig.org>, Eduardo Habkost <eduardo@habkost.net>, Marcel Apfelbaum <marcel.apfelbaum@gmail.com>, Yanan Wang <wangyanan55@huawei.com>, Zhao Liu <zhao1.liu@intel.com>, Reinoud Zandijk <reinoud@netbsd.org>, Sunil Muthuswamy <sunilmut@microsoft.com>, Eric Blake <eblake@redhat.com>, Markus Armbruster <armbru@redhat.com>, Peter Xu <peterx@redhat.com>, David Hildenbrand <david@redhat.com>, Peter Maydell <peter.maydell@linaro.org>, Alexander Graf <agraf@csgraf.de>

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[PATCH v3 56/68] accel/tcg: Unregister the RCU before exiting RR thread

Posted by Philippe Mathieu-Daudé 7 months, 1 week ago

Although unreachable, still unregister the RCU before exiting
the thread, as documented in "qemu/rcu.h":

 /*
  * Important !
  *
  * Each thread containing read-side critical sections must be registered
  * with rcu_register_thread() before calling rcu_read_lock().
  * rcu_unregister_thread() should be called before the thread exits.
  */

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
---
 accel/tcg/tcg-accel-ops-rr.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/accel/tcg/tcg-accel-ops-rr.c b/accel/tcg/tcg-accel-ops-rr.c
index 9578bc639cb..57a4bcab203 100644
--- a/accel/tcg/tcg-accel-ops-rr.c
+++ b/accel/tcg/tcg-accel-ops-rr.c
@@ -304,6 +304,8 @@ static void *rr_cpu_thread_fn(void *arg)
         rr_deal_with_unplugged_cpus();
     }
 
+    rcu_unregister_thread();
+
     g_assert_not_reached();
 }
 
-- 
2.49.0

Re: [PATCH v3 56/68] accel/tcg: Unregister the RCU before exiting RR thread

Posted by Richard Henderson 7 months, 1 week ago

On 7/1/25 08:40, Philippe Mathieu-Daudé wrote:
> Although unreachable, still unregister the RCU before exiting
> the thread, as documented in "qemu/rcu.h":
> 
>   /*
>    * Important !
>    *
>    * Each thread containing read-side critical sections must be registered
>    * with rcu_register_thread() before calling rcu_read_lock().
>    * rcu_unregister_thread() should be called before the thread exits.
>    */
> 
> Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> ---
>   accel/tcg/tcg-accel-ops-rr.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/accel/tcg/tcg-accel-ops-rr.c b/accel/tcg/tcg-accel-ops-rr.c
> index 9578bc639cb..57a4bcab203 100644
> --- a/accel/tcg/tcg-accel-ops-rr.c
> +++ b/accel/tcg/tcg-accel-ops-rr.c
> @@ -304,6 +304,8 @@ static void *rr_cpu_thread_fn(void *arg)
>           rr_deal_with_unplugged_cpus();
>       }
>   
> +    rcu_unregister_thread();
> +
>       g_assert_not_reached();
>   }
>   

I suppose.  This isn't like some clean exit or anything... we're about to abort.

Acked-by: Richard Henderson <richard.henderson@linaro.org>

r~