x86/irq: Plug vector setup race

Hogan reported a vector setup race, which overwrites the interrupt
descriptor in the per CPU vector array resulting in a disfunctional device.

CPU0				CPU1
				interrupt is raised in APIC IRR
				but not handled
  free_irq()
    per_cpu(vector_irq, CPU1)[vector] = VECTOR_SHUTDOWN;

  request_irq()			common_interrupt()
  				  d = this_cpu_read(vector_irq[vector]);

    per_cpu(vector_irq, CPU1)[vector] = desc;

    				  if (d == VECTOR_SHUTDOWN)
				    this_cpu_write(vector_irq[vector], VECTOR_UNUSED);

free_irq() cannot observe the pending vector in the CPU1 APIC as there is
no way to query the remote CPUs APIC IRR.

This requires that request_irq() uses the same vector/CPU as the one which
was freed, but this also can be triggered by a spurious interrupt.

Interestingly enough this problem managed to be hidden for more than a
decade.

Prevent this by reevaluating vector_irq under the vector lock, which is
held by the interrupt activation code when vector_irq is updated.

To avoid ifdeffery or IS_ENABLED() nonsense, move the
[un]lock_vector_lock() declarations out under the
CONFIG_IRQ_DOMAIN_HIERARCHY guard as it's only provided when
CONFIG_X86_LOCAL_APIC=y.

The current CONFIG_IRQ_DOMAIN_HIERARCHY guard is selected by
CONFIG_X86_LOCAL_APIC, but can also be selected by other parts of the
Kconfig system, which makes 32-bit UP builds with CONFIG_X86_LOCAL_APIC=n
fail.

Can we just get rid of this !APIC nonsense once and forever?

Fixes: 9345005 ("x86/irq: Fix do_IRQ() interrupt warning for cpu hotplug retriggered irqs")
Reported-by: Hogan Wang <[email protected]>
Signed-off-by: Thomas Gleixner <[email protected]>
Tested-by: Hogan Wang <[email protected]>
Link: https://lore.kernel.org/all/draft-87ikjhrhhh.ffs@tglx

Author: KAGA-KOKO

arch/x86/include/asm/hw_irq.h

@@ -92,21 +92,23 @@ struct irq_cfg {
 
 extern struct irq_cfg *irq_cfg(unsigned int irq);
 extern struct irq_cfg *irqd_cfg(struct irq_data *irq_data);
-extern void lock_vector_lock(void);
-extern void unlock_vector_lock(void);
 #ifdef CONFIG_SMP
 extern void vector_schedule_cleanup(struct irq_cfg *);
 extern void irq_complete_move(struct irq_cfg *cfg);
 #else
 static inline void vector_schedule_cleanup(struct irq_cfg *c) { }
 static inline void irq_complete_move(struct irq_cfg *c) { }
 #endif
-
 extern void apic_ack_edge(struct irq_data *data);
-#else	/*  CONFIG_IRQ_DOMAIN_HIERARCHY */
+#endif /* CONFIG_IRQ_DOMAIN_HIERARCHY */
+
+#ifdef CONFIG_X86_LOCAL_APIC
+extern void lock_vector_lock(void);
+extern void unlock_vector_lock(void);
+#else
 static inline void lock_vector_lock(void) {}
 static inline void unlock_vector_lock(void) {}
-#endif	/* CONFIG_IRQ_DOMAIN_HIERARCHY */
+#endif
 
 /* Statistics */
 extern atomic_t irq_err_count;

arch/x86/kernel/irq.c

@@ -256,26 +256,59 @@ static __always_inline void handle_irq(struct irq_desc *desc,
 		__handle_irq(desc, regs);
 }
 
-static __always_inline int call_irq_handler(int vector, struct pt_regs *regs)
+static struct irq_desc *reevaluate_vector(int vector)
 {
-	struct irq_desc *desc;
-	int ret = 0;
+	struct irq_desc *desc = __this_cpu_read(vector_irq[vector]);
+
+	if (!IS_ERR_OR_NULL(desc))
+		return desc;
+
+	if (desc == VECTOR_UNUSED)
+		pr_emerg_ratelimited("No irq handler for %d.%u\n", smp_processor_id(), vector);
+	else
+		__this_cpu_write(vector_irq[vector], VECTOR_UNUSED);
+	return NULL;
+}
+
+static __always_inline bool call_irq_handler(int vector, struct pt_regs *regs)
+{
+	struct irq_desc *desc = __this_cpu_read(vector_irq[vector]);
 
-	desc = __this_cpu_read(vector_irq[vector]);
 	if (likely(!IS_ERR_OR_NULL(desc))) {
 		handle_irq(desc, regs);
-	} else {
-		ret = -EINVAL;
-		if (desc == VECTOR_UNUSED) {
-			pr_emerg_ratelimited("%s: %d.%u No irq handler for vector\n",
-					     __func__, smp_processor_id(),
-					     vector);
-		} else {
-			__this_cpu_write(vector_irq[vector], VECTOR_UNUSED);
-		}
+		return true;
 	}
 
-	return ret;
+	/*
+	 * Reevaluate with vector_lock held to prevent a race against
+	 * request_irq() setting up the vector:
+	 *
+	 * CPU0				CPU1
+	 *				interrupt is raised in APIC IRR
+	 *				but not handled
+	 * free_irq()
+	 *   per_cpu(vector_irq, CPU1)[vector] = VECTOR_SHUTDOWN;
+	 *
+	 * request_irq()		common_interrupt()
+	 *				  d = this_cpu_read(vector_irq[vector]);
+	 *
+	 * per_cpu(vector_irq, CPU1)[vector] = desc;
+	 *
+	 *				  if (d == VECTOR_SHUTDOWN)
+	 *				    this_cpu_write(vector_irq[vector], VECTOR_UNUSED);
+	 *
+	 * This requires that the same vector on the same target CPU is
+	 * handed out or that a spurious interrupt hits that CPU/vector.
+	 */
+	lock_vector_lock();
+	desc = reevaluate_vector(vector);
+	unlock_vector_lock();
+
+	if (!desc)
+		return false;
+
+	handle_irq(desc, regs);
+	return true;
 }
 
 /*
@@ -289,7 +322,7 @@ DEFINE_IDTENTRY_IRQ(common_interrupt)
 	/* entry code tells RCU that we're not quiescent.  Check it. */
 	RCU_LOCKDEP_WARN(!rcu_is_watching(), "IRQ failed to wake up RCU");
 
-	if (unlikely(call_irq_handler(vector, regs)))
+	if (unlikely(!call_irq_handler(vector, regs)))
 		apic_eoi();
 
 	set_irq_regs(old_regs);