task #29600094

commit acd26bcf362708594ea081ef55140e37d0854ed2 upstream.
Backport summary: for 4.19 kernel ICX PCIe Gen4 support.

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: NThomas Gleixner <tglx@linutronix.de>
Tested-by: NKuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Reviewed-by: NKuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Acked-by: NMarc Zyngier <maz@kernel.org>
Link: https://lkml.kernel.org/r/20200306130623.990928309@linutronix.de

(cherry picked from commit acd26bcf362708594ea081ef55140e37d0854ed2)
Signed-off-by: NEthan Zhao <haifeng.zhao@intel.com>

Conflicts:
	include/linux/interrupt.h
	kernel/irq/debugfs.c
Signed-off-by: NArtie Ding <artie.ding@linux.alibaba.com>
Acked-by: NCaspar Zhang <caspar@linux.alibaba.com>