6.6-stable review patch. If anyone has any objections, please let me know.
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From: Juergen Gross jgross@suse.com
[ Upstream commit e64e7c74b99ec9e439abca75f522f4b98f220bd1 ]
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@amazon.co.uk Signed-off-by: Juergen Gross jgross@suse.com Tested-by: David Woodhouse dwmw@amazon.co.uk Acked-by: Stefano Stabellini sstabellini@kernel.org Signed-off-by: Juergen Gross jgross@suse.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/xen/events/events_base.c | 12 ++++++++---- 1 file changed, 8 insertions(+), 4 deletions(-)
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c index 1b2136fe0fa51..2cf0c2b693861 100644 --- a/drivers/xen/events/events_base.c +++ b/drivers/xen/events/events_base.c @@ -164,6 +164,8 @@ static DEFINE_PER_CPU(int [NR_VIRQS], virq_to_irq) = {[0 ... NR_VIRQS-1] = -1};
/* IRQ <-> IPI mapping */ static DEFINE_PER_CPU(int [XEN_NR_IPIS], ipi_to_irq) = {[0 ... XEN_NR_IPIS-1] = -1}; +/* Cache for IPI event channels - needed for hot cpu unplug (avoid RCU usage). */ +static DEFINE_PER_CPU(evtchn_port_t [XEN_NR_IPIS], ipi_to_evtchn) = {[0 ... XEN_NR_IPIS-1] = 0};
/* Event channel distribution data */ static atomic_t channels_on_cpu[NR_CPUS]; @@ -366,6 +368,7 @@ static int xen_irq_info_ipi_setup(unsigned cpu, info->u.ipi = ipi;
per_cpu(ipi_to_irq, cpu)[ipi] = irq; + per_cpu(ipi_to_evtchn, cpu)[ipi] = evtchn;
return xen_irq_info_common_setup(info, irq, IRQT_IPI, evtchn, 0); } @@ -981,6 +984,7 @@ static void __unbind_from_irq(unsigned int irq) break; case IRQT_IPI: per_cpu(ipi_to_irq, cpu)[ipi_from_irq(irq)] = -1; + per_cpu(ipi_to_evtchn, cpu)[ipi_from_irq(irq)] = 0; break; case IRQT_EVTCHN: dev = info->u.interdomain; @@ -1631,7 +1635,7 @@ EXPORT_SYMBOL_GPL(evtchn_put);
void xen_send_IPI_one(unsigned int cpu, enum ipi_vector vector) { - int irq; + evtchn_port_t evtchn;
#ifdef CONFIG_X86 if (unlikely(vector == XEN_NMI_VECTOR)) { @@ -1642,9 +1646,9 @@ void xen_send_IPI_one(unsigned int cpu, enum ipi_vector vector) return; } #endif - irq = per_cpu(ipi_to_irq, cpu)[vector]; - BUG_ON(irq < 0); - notify_remote_via_irq(irq); + evtchn = per_cpu(ipi_to_evtchn, cpu)[vector]; + BUG_ON(evtchn == 0); + notify_remote_via_evtchn(evtchn); }
struct evtchn_loop_ctrl {