[PATCH 3/6] sched/preempt: simplify irqentry_exit_cond_resched() callers

Mark Rutland
2021-11-09T17:26:07Z

Currently callers of irqentry_exit_cond_resched() need to be aware of
whether the function should be indirected via a static call, leading to
ugly ifdeffery in callers.

Save them the hassle with a static inline wrapper that does the right
thing. The raw_irqentry_exit_cond_resched() will also be useful in
subsequent patches which will add conditional wrappers for preemption
functions.

Note: in arch/x86/entry/common.c, xen_pv_evtchn_do_upcall() always calls
irqentry_exit_cond_resched() directly, even when PREEMPT_DYNAMIC is in
use. I believe this is a latent bug (which this patch corrects), but I'm
not entirely certain this wasn't deliberate.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
---
include/linux/entry-common.h | 9 ++++++---
kernel/entry/common.c | 12 ++++--------
2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
index a01ac1a0a292..dfd84c59b144 100644
--- a/include/linux/entry-common.h
+++ b/include/linux/entry-common.h
@@ -454,11 +454,14 @@ irqentry_state_t noinstr irqentry_enter(struct pt_regs *regs);
*
* Conditional reschedule with additional sanity checks.
*/
-void irqentry_exit_cond_resched(void);
+void raw_irqentry_exit_cond_resched(void);
#ifdef CONFIG_PREEMPT_DYNAMIC
-#define irqentry_exit_cond_resched_dynamic_enabled irqentry_exit_cond_resched
+#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, irqentry_exit_cond_resched);
+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()
#endif

/**
diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index d5a61d565ad5..3be0526e003d 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -380,7 +380,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
return ret;
}

-void irqentry_exit_cond_resched(void)
+void raw_irqentry_exit_cond_resched(void)
{
if (!preempt_count()) {
/* Sanity check RCU and thread stack */
@@ -392,7 +392,7 @@ void irqentry_exit_cond_resched(void)
}
}
#ifdef CONFIG_PREEMPT_DYNAMIC
-DEFINE_STATIC_CALL(irqentry_exit_cond_resched, irqentry_exit_cond_resched);
+DEFINE_STATIC_CALL(irqentry_exit_cond_resched, raw_irqentry_exit_cond_resched);
#endif

noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
@@ -420,13 +420,9 @@ noinstr void irqentry_exit(struct pt_regs *regs, irqentry_state_t state)
}

instrumentation_begin();
- if (IS_ENABLED(CONFIG_PREEMPTION)) {
-#ifdef CONFIG_PREEMPT_DYNAMIC
- static_call(irqentry_exit_cond_resched)();
-#else
+ if (IS_ENABLED(CONFIG_PREEMPTION))
irqentry_exit_cond_resched();
-#endif
- }
+
/* Covers both tracing and lockdep */
trace_hardirqs_on();
instrumentation_end();
--
2.11.0