Re: [PATCH] xen/events: avoid using info_for_irq() in xen_send_IPI_one()

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 30 Oct 2023, Juergen Gross wrote:
> xen_send_IPI_one() is being used by cpuhp_report_idle_dead() after
> it calls rcu_report_dead(), meaning that any RCU usage by
> xen_send_IPI_one() is a bad idea.
> 
> Unfortunately xen_send_IPI_one() is using notify_remote_via_irq()
> today, which is using irq_get_chip_data() via info_for_irq(). And
> irq_get_chip_data() in turn is using a maple-tree lookup requiring
> RCU.
> 
> Avoid this problem by caching the ipi event channels in another
> percpu variable, allowing the use notify_remote_via_evtchn() in
> xen_send_IPI_one().
> 
> Fixes: 721255b9826b ("genirq: Use a maple tree for interrupt descriptor 
> management")
> Reported-by: David Woodhouse <dwmw@xxxxxxxxxxxx>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Tested-by: David Woodhouse <dwmw@xxxxxxxxxxxx>

Acked-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>