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Date:   Thu, 25 Jun 2020 11:53:25 -0000
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Subject: [tip: sched/core] sched: Have sched_class_highest define by vmlinux.lds.h
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        "Peter Zijlstra (Intel)" <peterz@infradead.org>,
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The following commit has been merged into the sched/core branch of tip:

Commit-ID:     c3a340f7e7eadac7662ab104ceb16432e5a4c6b2
Gitweb:        https://git.kernel.org/tip/c3a340f7e7eadac7662ab104ceb16432e5a4c6b2
Author:        Steven Rostedt (VMware) <rostedt@goodmis.org>
AuthorDate:    Thu, 19 Dec 2019 16:44:53 -05:00
Committer:     Peter Zijlstra <peterz@infradead.org>
CommitterDate: Thu, 25 Jun 2020 13:45:44 +02:00

sched: Have sched_class_highest define by vmlinux.lds.h

Now that the sched_class descriptors are defined by the linker script, and
this needs to be aware of the existance of stop_sched_class when SMP is
enabled or not, as it is used as the "highest" priority when defined. Move
the declaration of sched_class_highest to the same location in the linker
script that inserts stop_sched_class, and this will also make it easier to
see what should be defined as the highest class, as this linker script
location defines the priorities as well.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20191219214558.682913590@goodmis.org
---
 include/asm-generic/vmlinux.lds.h |  5 ++++-
 kernel/sched/core.c               |  8 ++++++++
 kernel/sched/sched.h              | 17 +++++++++--------
 3 files changed, 21 insertions(+), 9 deletions(-)

diff --git a/include/asm-generic/vmlinux.lds.h b/include/asm-generic/vmlinux.lds.h
index 2186d7b..66fb84c 100644
--- a/include/asm-generic/vmlinux.lds.h
+++ b/include/asm-generic/vmlinux.lds.h
@@ -114,11 +114,14 @@
  * relation to each other.
  */
 #define SCHED_DATA				\
+	STRUCT_ALIGN();				\
+	__begin_sched_classes = .;		\
 	*(__idle_sched_class)			\
 	*(__fair_sched_class)			\
 	*(__rt_sched_class)			\
 	*(__dl_sched_class)			\
-	*(__stop_sched_class)
+	*(__stop_sched_class)			\
+	__end_sched_classes = .;
 
 /*
  * Align to a 32 byte boundary equal to the
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 0208b71..81640fe 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6646,6 +6646,14 @@ void __init sched_init(void)
 	unsigned long ptr = 0;
 	int i;
 
+	/* Make sure the linker didn't screw up */
+	BUG_ON(&idle_sched_class + 1 != &fair_sched_class ||
+	       &fair_sched_class + 1 != &rt_sched_class ||
+	       &rt_sched_class + 1   != &dl_sched_class);
+#ifdef CONFIG_SMP
+	BUG_ON(&dl_sched_class + 1 != &stop_sched_class);
+#endif
+
 	wait_bit_init();
 
 #ifdef CONFIG_FAIR_GROUP_SCHED
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3368876..4165c06 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1811,7 +1811,7 @@ struct sched_class {
 #ifdef CONFIG_FAIR_GROUP_SCHED
 	void (*task_change_group)(struct task_struct *p, int type);
 #endif
-};
+} __aligned(32); /* STRUCT_ALIGN(), vmlinux.lds.h */
 
 static inline void put_prev_task(struct rq *rq, struct task_struct *prev)
 {
@@ -1825,17 +1825,18 @@ static inline void set_next_task(struct rq *rq, struct task_struct *next)
 	next->sched_class->set_next_task(rq, next, false);
 }
 
-#ifdef CONFIG_SMP
-#define sched_class_highest (&stop_sched_class)
-#else
-#define sched_class_highest (&dl_sched_class)
-#endif
+/* Defined in include/asm-generic/vmlinux.lds.h */
+extern struct sched_class __begin_sched_classes[];
+extern struct sched_class __end_sched_classes[];
+
+#define sched_class_highest (__end_sched_classes - 1)
+#define sched_class_lowest  (__begin_sched_classes - 1)
 
 #define for_class_range(class, _from, _to) \
-	for (class = (_from); class != (_to); class = class->next)
+	for (class = (_from); class != (_to); class--)
 
 #define for_each_class(class) \
-	for_class_range(class, sched_class_highest, NULL)
+	for_class_range(class, sched_class_highest, sched_class_lowest)
 
 extern const struct sched_class stop_sched_class;
 extern const struct sched_class dl_sched_class;