[RFC PATCH 7/8] preempt/dynamic: Provide irqentry_exit_cond_resched() static call

[Frederic Weisbecker]

From: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx>

Provide static call to control IRQ preemption (called in CONFIG_PREEMPT)
so that we can override its behaviour when preempt= is overriden.

Since the default behaviour is full preemption, its call is
initialized to provide IRQ preemption when preempt= isn't passed.

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
---
 include/linux/entry-common.h |  4 ++++
 kernel/entry/common.c        | 10 +++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index ca86a00abe86..1401c93b65e1 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -2,6 +2,7 @@
 #ifndef __LINUX_ENTRYCOMMON_H
 #define __LINUX_ENTRYCOMMON_H
 
+#include <linux/static_call_types.h>
 #include <linux/tracehook.h>
 #include <linux/syscalls.h>
 #include <linux/seccomp.h>
@@ -453,6 +454,9 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
  * Conditional reschedule with additional sanity checks.
  */
 void irqentry_exit_cond_resched(void);
+#ifdef CONFIG_PREEMPT_DYNAMIC
+DECLARE_STATIC_CALL(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+#endif
 
 /**
  * irqentry_exit - Handle return from exception that used irqentry_enter()
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 378341642f94..84fa7ec28c36 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -393,6 +393,9 @@ void irqentry_exit_cond_resched(void)
 			preempt_schedule_irq();
 	}
 }
+#ifdef CONFIG_PREEMPT_DYNAMIC
+DEFINE_STATIC_CALL(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+#endif
 
 noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
 {
@@ -419,8 +422,13 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
 		}
 
 		instrumentation_begin();
-		if (IS_ENABLED(CONFIG_PREEMPTION))
+		if (IS_ENABLED(CONFIG_PREEMPTION)) {
+#ifdef CONFIG_PREEMT_DYNAMIC
+			static_call(irqentry_exit_cond_resched)();
+#else
 			irqentry_exit_cond_resched();
+#endif
+		}
 		/* Covers both tracing and lockdep */
 		trace_hardirqs_on();
 		instrumentation_end();
-- 
2.25.1