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

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index ef7fcef..2c639b6 100644 (file)
--- 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);
 }