Re: [PATCH v2 3/5] powerpc: Use preemption model accessors
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2021-11-11 04:55:34
Also in:
linux-kbuild, lkml
Valentin Schneider [off-list ref] writes:
Per PREEMPT_DYNAMIC, checking CONFIG_PREEMPT doesn't tell you the actual preemption model of the live kernel. Use the newly-introduced accessors instead. sched_init() -> preempt_dynamic_init() happens way before IRQs are set up, so this should be fine.
Despite the name interrupt_exit_kernel_prepare() is called before IRQs are setup, traps and page faults are "interrupts" here. So I'm not sure about adding that call there, because it will trigger a WARN if called early in boot, which will trigger a trap and depending on the context we may not survive. I'd be happier if we can make it a build-time check. cheers
quoted hunk ↗ jump to hunk
diff --git a/arch/powerpc/kernel/interrupt.c b/arch/powerpc/kernel/interrupt.c index de10a2697258..c56c10b59be3 100644 --- a/arch/powerpc/kernel/interrupt.c +++ b/arch/powerpc/kernel/interrupt.c@@ -552,7 +552,7 @@ notrace unsigned long interrupt_exit_kernel_prepare(struct pt_regs *regs) /* Returning to a kernel context with local irqs enabled. */ WARN_ON_ONCE(!(regs->msr & MSR_EE)); again: - if (IS_ENABLED(CONFIG_PREEMPT)) { + if (is_preempt_full()) { /* Return to preemptible kernel context */ if (unlikely(current_thread_info()->flags & _TIF_NEED_RESCHED)) { if (preempt_count() == 0)diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c index aac8c0412ff9..1cb31bbdc925 100644 --- a/arch/powerpc/kernel/traps.c +++ b/arch/powerpc/kernel/traps.c@@ -265,7 +265,7 @@ static int __die(const char *str, struct pt_regs *regs, long err) printk("%s PAGE_SIZE=%luK%s%s%s%s%s%s %s\n", IS_ENABLED(CONFIG_CPU_LITTLE_ENDIAN) ? "LE" : "BE", PAGE_SIZE / 1024, get_mmu_str(), - IS_ENABLED(CONFIG_PREEMPT) ? " PREEMPT" : "", + is_preempt_full() ? " PREEMPT" : "", IS_ENABLED(CONFIG_SMP) ? " SMP" : "", IS_ENABLED(CONFIG_SMP) ? (" NR_CPUS=" __stringify(NR_CPUS)) : "", debug_pagealloc_enabled() ? " DEBUG_PAGEALLOC" : "",-- 2.25.1