Re: [patch 00/13] preempt: Make preempt count unconditional

Matthew Wilcox
2020-09-16T19:26:32Z

On Mon, Sep 14, 2020 at 11:55:24PM +0200, Thomas Gleixner wrote:
> But just look at any check which uses preemptible(), especially those
> which check !preemptible():

hmm.

+++ b/include/linux/preempt.h
@@ -180,7 +180,9 @@ do { \

#define preempt_enable_no_resched() sched_preempt_enable_no_resched()

+#ifndef MODULE
#define preemptible() (preempt_count() == 0 && !irqs_disabled())
+#endif

#ifdef CONFIG_PREEMPTION
#define preempt_enable() \

$ git grep -w preemptible drivers
(slightly trimmed by hand to remove, eg, comments)
drivers/firmware/arm_sdei.c: WARN_ON_ONCE(preemptible());
drivers/firmware/arm_sdei.c: WARN_ON_ONCE(preemptible());
drivers/firmware/arm_sdei.c: WARN_ON_ONCE(preemptible());
drivers/firmware/arm_sdei.c: WARN_ON_ONCE(preemptible());
drivers/firmware/arm_sdei.c: WARN_ON(preemptible());
drivers/firmware/efi/efi-pstore.c: preemptible(), record->size, record->psi->buf);
drivers/irqchip/irq-gic-v4.c: WARN_ON(preemptible());
drivers/irqchip/irq-gic-v4.c: WARN_ON(preemptible());
drivers/scsi/hisi_sas/hisi_sas_main.c: if (!preemptible())
drivers/xen/time.c: BUG_ON(preemptible());

That only looks like two drivers that need more than WARNectomies.

Although maybe rcu_read_load_sched_held() or rcu_read_lock_any_held()
might get called from a module ...