genirq: prevent wakeup of freed irq thread

free_irq() can remove an irqaction while the corresponding interrupt
is in progress, but free_irq() sets action->thread to NULL
unconditionally, which might lead to a NULL pointer dereference in
handle_IRQ_event() when the hard interrupt context tries to wake up
the handler thread.

Prevent this by moving the thread stop after synchronize_irq(). No
need to set action->thread to NULL either as action is going to be
freed anyway.

This fixes a boot crash reported against preempt-rt which uses the
mainline irq threads code to implement full irq threading.

[ tglx: removed local irqthread variable ]

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 61c679d..d222515 100644 (file)
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -761,7 +761,6 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
 {
        struct irq_desc *desc = irq_to_desc(irq);
        struct irqaction *action, **action_ptr;
-       struct task_struct *irqthread;
        unsigned long flags;
 
        WARN(in_interrupt(), "Trying to free IRQ %d from IRQ context!\n", irq);
@@ -809,9 +808,6 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
                        desc->chip->disable(irq);
        }
 
-       irqthread = action->thread;
-       action->thread = NULL;
-
        spin_unlock_irqrestore(&desc->lock, flags);
 
        unregister_handler_proc(irq, action);
@@ -819,12 +815,6 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
        /* Make sure it's not being used on another CPU: */
        synchronize_irq(irq);
 
-       if (irqthread) {
-               if (!test_bit(IRQTF_DIED, &action->thread_flags))
-                       kthread_stop(irqthread);
-               put_task_struct(irqthread);
-       }
-
 #ifdef CONFIG_DEBUG_SHIRQ
        /*
         * It's a shared IRQ -- the driver ought to be prepared for an IRQ
@@ -840,6 +830,13 @@ static struct irqaction *__free_irq(unsigned int irq, void *dev_id)
                local_irq_restore(flags);
        }
 #endif
+
+       if (action->thread) {
+               if (!test_bit(IRQTF_DIED, &action->thread_flags))
+                       kthread_stop(action->thread);
+               put_task_struct(action->thread);
+       }
+
        return action;
 }