linux-kernel - [RFC PATCH v1.9 05/14] sched: horrible way to detect whether a task has been preempted

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Date:	Fri, 25 Mar 2016 14:34:52 -0500
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Jiri Kosina <jikos@...nel.org>, Jessica Yu <jeyu@...hat.com>,
	Miroslav Benes <mbenes@...e.cz>
Cc:	linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
	Vojtech Pavlik <vojtech@...e.com>
Subject: [RFC PATCH v1.9 05/14] sched: horrible way to detect whether a task has been preempted

This is a horrible way to detect whether a task has been preempted.
Come up with something better: task flag?  or is there already an
existing mechanism?

Signed-off-by: Josh Poimboeuf <jpoimboe@...hat.com>
---
 include/linux/sched.h | 11 ++++++++++-
 kernel/sched/core.c   | 26 ++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 589c478..62d0961 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -3239,4 +3239,13 @@ struct update_util_data {
 void cpufreq_set_update_util_data(int cpu, struct update_util_data *data);
 #endif /* CONFIG_CPU_FREQ */
 
-#endif
+#ifdef CONFIG_PREEMPT
+extern bool in_preempt_schedule_irq(unsigned long addr);
+#else
+static inline bool in_preempt_schedule_irq(unsigned long addr)
+{
+	return false;
+}
+#endif /* CONFIG_PREEMPT */
+
+#endif /* _LINUX_SCHED_H */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d8465ee..be1ef22 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3334,8 +3334,6 @@ asmlinkage __visible void __sched notrace preempt_schedule_notrace(void)
 }
 EXPORT_SYMBOL_GPL(preempt_schedule_notrace);
 
-#endif /* CONFIG_PREEMPT */
-
 /*
  * this is the entry point to schedule() from kernel preemption
  * off of irq context.
@@ -3360,8 +3358,32 @@ asmlinkage __visible void __sched preempt_schedule_irq(void)
 	} while (need_resched());
 
 	exception_exit(prev_state);
+
+	asm("preempt_schedule_irq_end:");
 }
 
+/*
+ * in_preempt_schedule_irq - determine if instruction address is inside the
+ *			     preempt_schedule_irq() function
+ *
+ * This is used when walking the stack of a task to determine whether an
+ * interrupt frame exists.
+ *
+ * NOTE: This function could return false if the address is in the function
+ * epilogue.  But it's good enough for our purposes, because we only care about
+ * addresses which have been saved on a stack.  If preempt_schedule_irq() is on
+ * the stack of a task, the saved address will always be prior to the epilogue.
+ */
+bool in_preempt_schedule_irq(unsigned long addr)
+{
+	extern void *preempt_schedule_irq_end;
+
+	return (addr >= (unsigned long)preempt_schedule_irq &&
+		addr <  (unsigned long)preempt_schedule_irq_end);
+}
+
+#endif /* CONFIG_PREEMPT */
+
 int default_wake_function(wait_queue_t *curr, unsigned mode, int wake_flags,
 			  void *key)
 {
-- 
2.4.3