powerpc/powernv: Make opal_event_shutdown() callable from IRQ context

[Michael Ellerman]

On Fri, 2017-09-29 at 03:58:02 UTC, Michael Ellerman wrote:
> In opal_event_shutdown() we free all the IRQs hanging off the
> opal_event_irqchip. However it's not safe to do so if we're called
> from IRQ context, because free_irq() wants to synchronise versus IRQ
> context. This can lead to warnings and a stuck system.
> 
> For example from sysrq-b:
> 
>   Trying to free IRQ 17 from IRQ context!
>   ------------[ cut here ]------------
>   WARNING: CPU: 0 PID: 0 at kernel/irq/manage.c:1461 __free_irq+0x398/0x8d0
>   ...
>   NIP __free_irq+0x398/0x8d0
>   LR __free_irq+0x394/0x8d0
>   Call Trace:
>     __free_irq+0x394/0x8d0 (unreliable)
>     free_irq+0xa4/0x140
>     opal_event_shutdown+0x128/0x180
>     opal_shutdown+0x1c/0xb0
>     pnv_shutdown+0x20/0x40
>     machine_restart+0x38/0x90
>     emergency_restart+0x28/0x40
>     sysrq_handle_reboot+0x24/0x40
>     __handle_sysrq+0x198/0x590
>     hvc_poll+0x48c/0x8c0
>     hvc_handle_interrupt+0x1c/0x50
>     __handle_irq_event_percpu+0xe8/0x6e0
>     handle_irq_event_percpu+0x34/0xe0
>     handle_irq_event+0xc4/0x210
>     handle_level_irq+0x250/0x770
>     generic_handle_irq+0x5c/0xa0
>     opal_handle_events+0x11c/0x240
>     opal_interrupt+0x38/0x50
>     __handle_irq_event_percpu+0xe8/0x6e0
>     handle_irq_event_percpu+0x34/0xe0
>     handle_irq_event+0xc4/0x210
>     handle_fasteoi_irq+0x174/0xa10
>     generic_handle_irq+0x5c/0xa0
>     __do_irq+0xbc/0x4e0
>     call_do_irq+0x14/0x24
>     do_IRQ+0x18c/0x540
>     hardware_interrupt_common+0x158/0x180
> 
> We can avoid that by using disable_irq_nosync() rather than
> free_irq(). Although it doesn't fully free the IRQ, it should be
> sufficient when we're shutting down, particularly in an emergency.
> 
> Add an in_interrupt() check and use free_irq() when we're shutting
> down normally. It's probably OK to use disable_irq_nosync() in that
> case too, but for now it's safer to leave that behaviour as-is.
> 
> Fixes: 9f0fd0499d30 ("powerpc/powernv: Add a virtual irqchip for opal events")
> Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
> Acked-by: Balbir Singh <bsingharora at gmail.com>

Applied to powerpc next.

https://git.kernel.org/powerpc/c/c6baa077b784c3b37391a8c11f433e

cheers