• Thomas Gleixner's avatar
    genirq: Add optional hardware synchronization for shutdown · 62e04686
    Thomas Gleixner authored
    free_irq() ensures that no hardware interrupt handler is executing on a
    different CPU before actually releasing resources and deactivating the
    interrupt completely in a domain hierarchy.
    
    But that does not catch the case where the interrupt is on flight at the
    hardware level but not yet serviced by the target CPU. That creates an
    interesing race condition:
    
       CPU 0                  CPU 1               IRQ CHIP
    
                                                  interrupt is raised
                                                  sent to CPU1
    			  Unable to handle
    			  immediately
    			  (interrupts off,
    			   deep idle delay)
       mask()
       ...
       free()
         shutdown()
         synchronize_irq()
         release_resources()
                              do_IRQ()
                                -> resources are not available
    
    That might be harmless and just trigger a spurious interrupt warning, but
    some interrupt chips might get into a wedged state.
    
    Utilize the existing irq_get_irqchip_state() callback for the
    synchronization in free_irq().
    
    synchronize_hardirq() is not using this mechanism as it might actually
    deadlock unter certain conditions, e.g. when called with interrupts
    disabled and the target CPU is the one on which the synchronization is
    invoked. synchronize_irq() uses it because that function cannot be called
    from non preemtible contexts as it might sleep.
    
    No functional change intended and according to Marc the existing GIC
    implementations where the driver supports the callback should be able
    to cope with that core change. Famous last words.
    
    Fixes: 464d1230 ("x86/vector: Switch IOAPIC to global reservation mode")
    Reported-by: default avatarRobert Hodaszi <Robert.Hodaszi@digi.com>
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Reviewed-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    Tested-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    Link: https://lkml.kernel.org/r/20190628111440.279463375@linutronix.de
    62e04686
internals.h 13.9 KB