Commit 8e12ab7c authored Feb 14, 2022 by Mark Rutland Committed by Peter Zijlstra Feb 19, 2022

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@arm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/r/20220214165216.2231574-7-mark.rutland@arm.com

parent 99cf983c

arch/arm64/kernel/entry-common.c

+11 −9

Original line number	Diff line number	Diff line
		@@ -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
		@@ -438,13 +447,6 @@ 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();

		exit_to_kernel_mode(regs);