linux-kernel - [PATCH RT] sched: let softirq_count() return !0 if inside local_bh

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Message-ID: <20180517102214.orea3ol6dj7wvpf5@linutronix.de>
Date:   Thu, 17 May 2018 12:22:14 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-rt-users@...r.kernel.org
Cc:     linux-kernel@...r.kernel.org, tglx@...utronix.de,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH RT] sched: let softirq_count() return !0 if inside
 local_bh_disable()ed section

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@...utronix.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