[PATCH] Debug shared irqs

Drivers registering IRQ handlers with SA_SHIRQ really ought to be able to
handle an interrupt happening before request_irq() returns.  They also
ought to be able to handle an interrupt happening during the start of their
call to free_irq().  Let's test that hypothesis....

[bunk@stusta.de: Kconfig fixes]
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 42 insertions, 0 deletions

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 8b961adc3bd2..400b12a63649 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -357,6 +357,7 @@ void free_irq(unsigned int irq, void *dev_id)
         struct irq_desc *desc;
         struct irqaction **p;
         unsigned long flags;
+        irqreturn_t (*handler)(int, void *) = NULL;
 
         WARN_ON(in_interrupt());
         if (irq >= NR_IRQS)
@@ -396,6 +397,8 @@ void free_irq(unsigned int irq, void *dev_id)
 
                         /* Make sure it's not being used on another CPU */
                         synchronize_irq(irq);
+                        if (action->flags & IRQF_SHARED)
+                                handler = action->handler;
                         kfree(action);
                         return;
                 }
@@ -403,6 +406,17 @@ void free_irq(unsigned int irq, void *dev_id)
                 spin_unlock_irqrestore(&desc->lock, flags);
                 return;
         }
+#ifdef CONFIG_DEBUG_SHIRQ
+        if (handler) {
+                /*
+                 * It's a shared IRQ -- the driver ought to be prepared for it
+                 * to happen even now it's being freed, so let's make sure....
+                 * We do this after actually deregistering it, to make sure that
+                 * a 'real' IRQ doesn't run in parallel with our fake
+                 */
+                handler(irq, dev_id);
+        }
+#endif
 }
 EXPORT_SYMBOL(free_irq);
 
@@ -475,6 +489,25 @@ int request_irq(unsigned int irq, irq_handler_t handler,
 
         select_smp_affinity(irq);
 
+#ifdef CONFIG_DEBUG_SHIRQ
+        if (irqflags & IRQF_SHARED) {
+                /*
+                 * It's a shared IRQ -- the driver ought to be prepared for it
+                 * to happen immediately, so let's make sure....
+                 * We do this before actually registering it, to make sure that
+                 * a 'real' IRQ doesn't run in parallel with our fake
+                 */
+                if (irqflags & IRQF_DISABLED) {
+                        unsigned long flags;
+
+                        local_irq_save(flags);
+                        handler(irq, dev_id);
+                        local_irq_restore(flags);
+                } else
+                        handler(irq, dev_id);
+        }
+#endif
+
         retval = setup_irq(irq, action);
         if (retval)
                 kfree(action);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 356a5ab8279c..63f04c15e6f5 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -77,6 +77,15 @@ config DEBUG_KERNEL
           Say Y here if you are developing drivers or trying to debug and
           identify kernel problems.
 
+config DEBUG_SHIRQ
+        bool "Debug shared IRQ handlers"
+        depends on DEBUG_KERNEL && GENERIC_HARDIRQS
+        help
+          Enable this to generate a spurious interrupt as soon as a shared
+          interrupt handler is registered, and just before one is deregistered.
+          Drivers ought to be able to handle interrupts coming in at those
+          points; some don't and need to be caught.
+
 config LOG_BUF_SHIFT
         int "Kernel log buffer size (16 => 64KB, 17 => 128KB)" if DEBUG_KERNEL
         range 12 21