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sched: Reverse sched_class layout

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Because GCC-12 is fully stupid about array bounds and it's just really
hard to get a solid array definition from a linker script, flip the
array order to avoid needing negative offsets :-/

This makes the whole relational pointer magic a little less obvious, but
alas.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lkml.kernel.org/r/YoOLLmLG7HRTXeEm@hirez.programming.kicks-ass.net
This commit is contained in:
Peter Zijlstra 2022-05-17 13:46:54 +02:00
parent 734387ec2f
commit 546a3fee17
3 changed files with 20 additions and 19 deletions
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12
include/asm-generic/vmlinux.lds.h
View File

@ -126,13 +126,13 @@
*/
#define SCHED_DATA \
STRUCT_ALIGN(); \
__begin_sched_classes = .; \
*(__idle_sched_class) \
*(__fair_sched_class) \
*(__rt_sched_class) \
*(__dl_sched_class) \
__sched_class_highest = .; \
*(__stop_sched_class) \
__end_sched_classes = .;
*(__dl_sched_class) \
*(__rt_sched_class) \
*(__fair_sched_class) \
*(__idle_sched_class) \
__sched_class_lowest = .;
/* The actual configuration determine if the init/exit sections
* are handled as text/data or they can be discarded (which

12
kernel/sched/core.c
View File

@ -2193,7 +2193,7 @@ void check_preempt_curr(struct rq *rq, struct task_struct *p, int flags)
{
if (p->sched_class == rq->curr->sched_class)
rq->curr->sched_class->check_preempt_curr(rq, p, flags);
else if (p->sched_class > rq->curr->sched_class)
else if (sched_class_above(p->sched_class, rq->curr->sched_class))
resched_curr(rq);
/*
@ -5692,7 +5692,7 @@ __pick_next_task(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
* higher scheduling class, because otherwise those lose the
* opportunity to pull in more work from other CPUs.
*/
if (likely(prev->sched_class <= &fair_sched_class &&
if (likely(!sched_class_above(prev->sched_class, &fair_sched_class) &&
rq->nr_running == rq->cfs.h_nr_running)) {
p = pick_next_task_fair(rq, prev, rf);
@ -9472,11 +9472,11 @@ void __init sched_init(void)
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);
BUG_ON(&idle_sched_class != &fair_sched_class + 1 ||
&fair_sched_class != &rt_sched_class + 1 ||
&rt_sched_class != &dl_sched_class + 1);
#ifdef CONFIG_SMP
BUG_ON(&dl_sched_class + 1 != &stop_sched_class);
BUG_ON(&dl_sched_class != &stop_sched_class + 1);
#endif
wait_bit_init();

15
kernel/sched/sched.h
View File

@ -2177,6 +2177,8 @@ static inline void set_next_task(struct rq *rq, struct task_struct *next)
*
* include/asm-generic/vmlinux.lds.h
*
* *CAREFUL* they are laid out in *REVERSE* order!!!
*
* Also enforce alignment on the instance, not the type, to guarantee layout.
*/
#define DEFINE_SCHED_CLASS(name) \
@ -2185,17 +2187,16 @@ const struct sched_class name##_sched_class \
__section("__" #name "_sched_class")
/* 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)
extern struct sched_class __sched_class_highest[];
extern struct sched_class __sched_class_lowest[];
#define for_class_range(class, _from, _to) \
for (class = (_from); class != (_to); class--)
for (class = (_from); class < (_to); class++)
#define for_each_class(class) \
for_class_range(class, sched_class_highest, sched_class_lowest)
for_class_range(class, __sched_class_highest, __sched_class_lowest)
#define sched_class_above(_a, _b) ((_a) < (_b))
extern const struct sched_class stop_sched_class;
extern const struct sched_class dl_sched_class;