linux-kernel - [PATCH v2 3/7] sched/preempt: simplify irqentry_exit_cond

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Date:   Fri,  4 Feb 2022 15:05:53 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     ardb@...nel.org, bp@...en8.de, catalin.marinas@....com,
        dave.hansen@...ux.intel.com, frederic@...nel.org,
        james.morse@....com, joey.gouly@....com, juri.lelli@...hat.com,
        linux-kernel@...r.kernel.org, luto@...nel.org,
        mark.rutland@....com, mingo@...hat.com, peterz@...radead.org,
        tglx@...utronix.de, valentin.schneider@....com, will@...nel.org
Subject: [PATCH v2 3/7] sched/preempt: simplify irqentry_exit_cond_resched() callers

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@....com>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Ard Biesheuvel <ardb@...nel.org>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Cc: Frederic Weisbecker <frederic@...nel.org>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Juri Lelli <juri.lelli@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Valentin Schneider <valentin.schneider@....com>
---
 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 bad713684c2e..1739ca79613b 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();
-- 
2.30.2