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Subject[RFC PATCH v1.9 05/14] sched: horrible way to detect whether a task has been preempted
Date
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@redhat.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
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