On Mon, Feb 07, 2022 at 12:57:08PM +0100, Frederic Weisbecker wrote:

On Fri, Feb 04, 2022 at 03:05:55PM +0000, Mark Rutland wrote:

quoted

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index dfd84c59b144..141952f4fee8 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h

@@ -456,13 +456,19 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
  */
 void raw_irqentry_exit_cond_resched(void);
 #ifdef CONFIG_PREEMPT_DYNAMIC
+#if defined(CONFIG_HAVE_PREEMPT_DYNAMIC_CALL)
 #define irqentry_exit_cond_resched_dynamic_enabled	raw_irqentry_exit_cond_resched
 #define irqentry_exit_cond_resched_dynamic_disabled	NULL
 DECLARE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
 #define irqentry_exit_cond_resched()	static_call(irqentry_exit_cond_resched)()
-#else
-#define irqentry_exit_cond_resched()	raw_irqentry_exit_cond_resched()
+#elif defined(CONFIG_HAVE_PREEMPT_DYNAMIC_KEY)
+DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);

If CONFIG_PREEMPT && CONFIG_PREEMPT_DYNAMIC and no "preempt=" parameter is
passed, nothing is overriden on boot. So you need to either have cond_resched
and might_resched initially disabled (STATIC_KEY_FALSE?) or call
sched_dynamic_update() from preempt_dynamic_init() also when CONFIG_PREEMPT=y.

Ah; good spot. I'd missed that those were initialized to RET0.

I've changed those two to DECLARE_STATIC_KEY_FALSE(), which defaults those to
disabled, e.g.

| <dynamic_cond_resched>:
|        bti     c
|        nop     // <-------- `b <dynamic_cond_resched+0x10>` when enabled
|        mov     w0, #0x0
|        ret
|        mrs     x0, sp_el0
|        ldr     x0, [x0, #8]
|        cbnz    x0, 9d8 <dynamic_cond_resched+0x8>
|        paciasp
|        stp     x29, x30, [sp, #-16]!
|        mov     x29, sp
|        bl      900 <preempt_schedule_common>
|        mov     w0, #0x1
|        ldp     x29, x30, [sp], #16
|        autiasp
|        ret

Thanks,
Mark.

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