[PATCH RT] sched: let softirq_count() return !0 if inside local_bh_disable()ed section

[PATCH RT] sched: let softirq_count() return !0 if inside local_bh_disable()ed section

[Sebastian Andrzej Siewior]

I don't see a reason why softirq_count() shouldn't reflect the fact that
we are within a local_bh_disable() section. I *think* it was done
primary because in RT the softirq is slightly different (and
preemptible) and it broke some of RCU's assumptions.
I don't see any fallout with this change. Furthermore, all checks like
"WARN_ON(!softirq_count())" will work and we can drop the workaround we
currently have in the queue.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 include/linux/preempt.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/preempt.h b/include/linux/preempt.h
index 0591df500e9d..d8c05a2626ca 100644
--- a/include/linux/preempt.h
+++ b/include/linux/preempt.h
@@ -91,7 +91,7 @@
 # define softirq_count()	(preempt_count() & SOFTIRQ_MASK)
 # define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
 #else
-# define softirq_count()	(0UL)
+# define softirq_count()	(current->softirq_nestcnt)
 extern int in_serving_softirq(void);
 #endif
 
-- 
2.17.0

Re: [PATCH RT] sched: let softirq_count() return !0 if inside local_bh_disable()ed section

[Steven Rostedt]

On Thu, 17 May 2018 12:22:14 +0200
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> I don't see a reason why softirq_count() shouldn't reflect the fact that
> we are within a local_bh_disable() section. I *think* it was done
> primary because in RT the softirq is slightly different (and
> preemptible) and it broke some of RCU's assumptions.
> I don't see any fallout with this change. Furthermore, all checks like
> "WARN_ON(!softirq_count())" will work and we can drop the workaround we
> currently have in the queue.

Looks to keep the paradigm closer to vanilla Linux to me.

Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>

-- Steve

> 
> Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> ---
>  include/linux/preempt.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/preempt.h b/include/linux/preempt.h
> index 0591df500e9d..d8c05a2626ca 100644
> --- a/include/linux/preempt.h
> +++ b/include/linux/preempt.h
> @@ -91,7 +91,7 @@
>  # define softirq_count()	(preempt_count() & SOFTIRQ_MASK)
>  # define in_serving_softirq()	(softirq_count() & SOFTIRQ_OFFSET)
>  #else
> -# define softirq_count()	(0UL)
> +# define softirq_count()	(current->softirq_nestcnt)
>  extern int in_serving_softirq(void);
>  #endif
>