x86/irq: Handle spurious interrupt after shutdown gracefully

Since the rework of the vector management, warnings about spurious
interrupts have been reported. Robert provided some more information and
did an initial analysis. The following situation leads to these warnings:

   CPU 0                  CPU 1               IO_APIC

                                              interrupt is raised
                                              sent to CPU1
			  Unable to handle
			  immediately
			  (interrupts off,
			   deep idle delay)
   mask()
   ...
   free()
     shutdown()
     synchronize_irq()
     clear_vector()
                          do_IRQ()
                            -> vector is clear

Before the rework the vector entries of legacy interrupts were statically
assigned and occupied precious vector space while most of them were
unused. Due to that the above situation was handled silently because the
vector was handled and the core handler of the assigned interrupt
descriptor noticed that it is shut down and returned.

While this has been usually observed with legacy interrupts, this situation
is not limited to them. Any other interrupt source, e.g. MSI, can cause the
same issue.

After adding proper synchronization for level triggered interrupts, this
can only happen for edge triggered interrupts where the IO-APIC obviously
cannot provide information about interrupts in flight.

While the spurious warning is actually harmless in this case it worries
users and driver developers.

Handle it gracefully by marking the vector entry as VECTOR_SHUTDOWN instead
of VECTOR_UNUSED when the vector is freed up.

If that above late handling happens the spurious detector will not complain
and switch the entry to VECTOR_UNUSED. Any subsequent spurious interrupt on
that line will trigger the spurious warning as before.

Fixes: 464d12309e1b ("x86/vector: Switch IOAPIC to global reservation mode")
Reported-by: Robert Hodaszi <Robert.Hodaszi@digi.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>-
Tested-by: Robert Hodaszi <Robert.Hodaszi@digi.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Link: https://lkml.kernel.org/r/20190628111440.459647741@linutronix.de

diff --git a/arch/x86/include/asm/hw_irq.h b/arch/x86/include/asm/hw_irq.h
index 32e666e1231e77f128252b2f9354f708081cafdb..626e1ac6516ee63628765d83187011afff887d49 100644 (file)
--- a/arch/x86/include/asm/hw_irq.h
+++ b/arch/x86/include/asm/hw_irq.h
@@ -151,7 +151,8 @@ extern char irq_entries_start[];
 #endif
 
 #define VECTOR_UNUSED          NULL
-#define VECTOR_RETRIGGERED     ((void *)~0UL)
+#define VECTOR_SHUTDOWN                ((void *)~0UL)
+#define VECTOR_RETRIGGERED     ((void *)~1UL)
 
 typedef struct irq_desc* vector_irq_t[NR_VECTORS];
 DECLARE_PER_CPU(vector_irq_t, vector_irq);

diff --git a/arch/x86/kernel/apic/vector.c b/arch/x86/kernel/apic/vector.c
index 3173e07d3791bef133a94563db30299c1b53abca..1c6d1d5f28d3fdaeb1c9e047658b2d5767ff2f13 100644 (file)
--- a/arch/x86/kernel/apic/vector.c
+++ b/arch/x86/kernel/apic/vector.c
@@ -343,7 +343,7 @@ static void clear_irq_vector(struct irq_data *irqd)
        trace_vector_clear(irqd->irq, vector, apicd->cpu, apicd->prev_vector,
                           apicd->prev_cpu);
 
-       per_cpu(vector_irq, apicd->cpu)[vector] = VECTOR_UNUSED;
+       per_cpu(vector_irq, apicd->cpu)[vector] = VECTOR_SHUTDOWN;
        irq_matrix_free(vector_matrix, apicd->cpu, vector, managed);
        apicd->vector = 0;
 
@@ -352,7 +352,7 @@ static void clear_irq_vector(struct irq_data *irqd)
        if (!vector)
                return;
 
-       per_cpu(vector_irq, apicd->prev_cpu)[vector] = VECTOR_UNUSED;
+       per_cpu(vector_irq, apicd->prev_cpu)[vector] = VECTOR_SHUTDOWN;
        irq_matrix_free(vector_matrix, apicd->prev_cpu, vector, managed);
        apicd->prev_vector = 0;
        apicd->move_in_progress = 0;

diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index 59b5f2ea7c2f32d8c02181be432262b2df97ea1a..a975246074b5c571e7346228553467e8f8244895 100644 (file)
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -246,7 +246,7 @@ __visible unsigned int __irq_entry do_IRQ(struct pt_regs *regs)
        if (!handle_irq(desc, regs)) {
                ack_APIC_irq();
 
-               if (desc != VECTOR_RETRIGGERED) {
+               if (desc != VECTOR_RETRIGGERED && desc != VECTOR_SHUTDOWN) {
                        pr_emerg_ratelimited("%s: %d.%d No irq handler for vector\n",
                                             __func__, smp_processor_id(),
                                             vector);