genirq: Provide interrupt injection mechanism

Error injection mechanisms need a half ways safe way to inject interrupts as
invoking generic_handle_irq() or the actual device interrupt handler
directly from e.g. a debugfs write is not guaranteed to be safe.

On x86 generic_handle_irq() is unsafe due to the hardware trainwreck which
is the base of x86 interrupt delivery and affinity management.

Move the irq debugfs injection code into a separate function which can be
used by error injection code as well.

The implementation prevents at least that state is corrupted, but it cannot
close a very tiny race window on x86 which might result in a stale and not
serviced device interrupt under very unlikely circumstances.

This is explicitly for debugging and testing and not for production use or
abuse in random driver code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Link: https://lkml.kernel.org/r/20200306130623.990928309@linutronix.de

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index c5fe60ec6b84..80f637c3a6f3 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -248,6 +248,8 @@ extern void enable_percpu_nmi(unsigned int irq, unsigned int type);
 extern int prepare_percpu_nmi(unsigned int irq);
 extern void teardown_percpu_nmi(unsigned int irq);
 
+extern int irq_inject_interrupt(unsigned int irq);
+
 /* The following three functions are for the core kernel use only. */
 extern void suspend_device_irqs(void);
 extern void resume_device_irqs(void);