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

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Date:   Wed, 16 Sep 2020 20:23:52 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
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Subject: Re: [patch 00/13] preempt: Make preempt count unconditional

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 ...