linux-kernel - [tip: sched/core] arm64: entry: Centralize preemption decision

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Date:   Sat, 19 Feb 2022 10:21:24 -0000
From:   "tip-bot2 for Mark Rutland" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: sched/core] arm64: entry: Centralize preemption decision

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     8e12ab7c0e9f73ebfbcd6d37ece738f1825d58c8
Gitweb:        https://git.kernel.org/tip/8e12ab7c0e9f73ebfbcd6d37ece738f1825d58c8
Author:        Mark Rutland <mark.rutland@....com>
AuthorDate:    Mon, 14 Feb 2022 16:52:15 
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Sat, 19 Feb 2022 11:11:08 +01:00

arm64: entry: Centralize preemption decision

For historical reasons, the decision of whether or not to preempt is
spread across arm64_preempt_schedule_irq() and __el1_irq(), and it would
be clearer if this were all in one place.

Also, arm64_preempt_schedule_irq() calls lockdep_assert_irqs_disabled(),
but this is redundant, as we have a subsequent identical assertion in
__exit_to_kernel_mode(), and preempt_schedule_irq() will
BUG_ON(!irqs_disabled()) anyway.

This patch removes the redundant assertion and centralizes the
preemption decision making within arm64_preempt_schedule_irq().

Other than the slight change to assertion behaviour, there should be no
functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@....com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Acked-by: Ard Biesheuvel <ardb@...nel.org>
Acked-by: Catalin Marinas <catalin.marinas@....com>
Acked-by: Frederic Weisbecker <frederic@...nel.org>
Link: https://lore.kernel.org/r/20220214165216.2231574-7-mark.rutland@arm.com
---
 arch/arm64/kernel/entry-common.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index ef7fcef..2c639b6 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -222,7 +222,16 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs *regs)
 
 static void __sched arm64_preempt_schedule_irq(void)
 {
-	lockdep_assert_irqs_disabled();
+	if (!IS_ENABLED(CONFIG_PREEMPTION))
+		return;
+
+	/*
+	 * Note: thread_info::preempt_count includes both thread_info::count
+	 * and thread_info::need_resched, and is not equivalent to
+	 * preempt_count().
+	 */
+	if (READ_ONCE(current_thread_info()->preempt_count) != 0)
+		return;
 
 	/*
 	 * DAIF.DA are cleared at the start of IRQ/FIQ handling, and when GIC
@@ -438,14 +447,7 @@ static __always_inline void __el1_irq(struct pt_regs *regs,
 	do_interrupt_handler(regs, handler);
 	irq_exit_rcu();
 
-	/*
-	 * Note: thread_info::preempt_count includes both thread_info::count
-	 * and thread_info::need_resched, and is not equivalent to
-	 * preempt_count().
-	 */
-	if (IS_ENABLED(CONFIG_PREEMPTION) &&
-	    READ_ONCE(current_thread_info()->preempt_count) == 0)
-		arm64_preempt_schedule_irq();
+	arm64_preempt_schedule_irq();
 
 	exit_to_kernel_mode(regs);
 }