linux-kernel - [PATCH] tracing/irqtrace: only call trace_hardirqs

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Message-Id: <20171116161506.19691-1-npiggin@gmail.com>
Date:   Fri, 17 Nov 2017 02:15:06 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     unlisted-recipients:; (no To-header on input)
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: [PATCH] tracing/irqtrace: only call trace_hardirqs_on/off when state changes

In local_irq_save and local_irq_restore, only call irq tracing when
the flag state acutally changes. It is not unexpected for the state
to go disable->disable.

This allows the irq tracing code to better track superfluous
enables and disables, and in future could issue warnings. For the
most part they are harmless, but they can indicate that the caller
has lost track of its irq state.

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: linux-kernel@...r.kernel.org
Signed-off-by: Nicholas Piggin <npiggin@...il.com>
---
I wonder what you think of this patch? After a small fix to
init/main.c and some powerpc fixes, I was able to use this patch 
and a change to warn in the lockdep code in case of redundant ops,
to verify there were no local_irq_enable() when enabled, or
local_irq_disable() when disabled (which was implicated in a bug).

Lots of code to verify so we can't do this immediately, but I
think it's cleaner to enforce the rule?

Thanks,
Nick

 include/linux/irqflags.h | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/include/linux/irqflags.h b/include/linux/irqflags.h
index 46cb57d5eb13..82287e1c6c52 100644
--- a/include/linux/irqflags.h
+++ b/include/linux/irqflags.h
@@ -110,7 +110,8 @@ do {						\
 #define local_irq_save(flags)				\
 	do {						\
 		raw_local_irq_save(flags);		\
-		trace_hardirqs_off();			\
+		if (!raw_irqs_disabled_flags(flags))	\
+			trace_hardirqs_off();		\
 	} while (0)
 
 
@@ -118,9 +119,11 @@ do {						\
 	do {						\
 		if (raw_irqs_disabled_flags(flags)) {	\
 			raw_local_irq_restore(flags);	\
-			trace_hardirqs_off();		\
+			if (!irqs_disabled())		\
+				trace_hardirqs_off();	\
 		} else {				\
-			trace_hardirqs_on();		\
+			if (irqs_disabled())		\
+				trace_hardirqs_on();	\
 			raw_local_irq_restore(flags);	\
 		}					\
 	} while (0)
-- 
2.15.0