linux-kernel - [PATCH 2/5] context_tracking: Don't implement exception_enter/exit() on CONFIG_HAVE_CONTEXT_TRACKING

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Date:   Tue, 27 Oct 2020 16:08:24 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Phil Auld <pauld@...hat.com>,
        Marcelo Tosatti <mtosatti@...hat.com>
Subject: [PATCH 2/5] context_tracking:  Don't implement exception_enter/exit() on CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK

An architecture that provides this Kconfig feature doesn't need to
store the context tracking state on the task stack because its entry
code has been sanitized such that fragile path aren't preemptible
and special use of tracing and RCU read side critical sections in these
areas have been explicitly annotated.

Hence the exception_enter()/exception_exit() couple doesn't need to be
implemented in this case.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Paul E. McKenney <paulmck@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Phil Auld <pauld@...hat.com>
Cc: Thomas Gleixner <tglx@...utronix.de>
---
 include/linux/context_tracking.h | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/linux/context_tracking.h b/include/linux/context_tracking.h
index d53cd331c4dd..bceb06498521 100644
--- a/include/linux/context_tracking.h
+++ b/include/linux/context_tracking.h
@@ -51,7 +51,8 @@ static inline enum ctx_state exception_enter(void)
 {
 	enum ctx_state prev_ctx;
 
-	if (!context_tracking_enabled())
+	if (IS_ENABLED(CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK) ||
+	    !context_tracking_enabled())
 		return 0;
 
 	prev_ctx = this_cpu_read(context_tracking.state);
@@ -63,7 +64,8 @@ static inline enum ctx_state exception_enter(void)
 
 static inline void exception_exit(enum ctx_state prev_ctx)
 {
-	if (context_tracking_enabled()) {
+	if (!IS_ENABLED(CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK) &&
+	    context_tracking_enabled()) {
 		if (prev_ctx != CONTEXT_KERNEL)
 			context_tracking_enter(prev_ctx);
 	}
-- 
2.25.1