Messages in this thread | | | Subject | Re: [PATCH v2 3/8] xen/events: avoid handling the same event on two cpus at the same time | From | Julien Grall <> | Date | Sun, 14 Feb 2021 21:34:31 +0000 |
| |
Hi Juergen,
On 11/02/2021 10:16, Juergen Gross wrote: > When changing the cpu affinity of an event it can happen today that > (with some unlucky timing) the same event will be handled on the old > and the new cpu at the same time. > > Avoid that by adding an "event active" flag to the per-event data and > call the handler only if this flag isn't set. > > Reported-by: Julien Grall <julien@xen.org> > Signed-off-by: Juergen Gross <jgross@suse.com> > --- > V2: > - new patch > --- > drivers/xen/events/events_base.c | 19 +++++++++++++++---- > 1 file changed, 15 insertions(+), 4 deletions(-) > > diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c > index e157e7506830..f7e22330dcef 100644 > --- a/drivers/xen/events/events_base.c > +++ b/drivers/xen/events/events_base.c > @@ -102,6 +102,7 @@ struct irq_info { > #define EVT_MASK_REASON_EXPLICIT 0x01 > #define EVT_MASK_REASON_TEMPORARY 0x02 > #define EVT_MASK_REASON_EOI_PENDING 0x04 > + u8 is_active; /* Is event just being handled? */ > unsigned irq; > evtchn_port_t evtchn; /* event channel */ > unsigned short cpu; /* cpu bound */ > @@ -622,6 +623,7 @@ static void xen_irq_lateeoi_locked(struct irq_info *info, bool spurious) > } > > info->eoi_time = 0; > + smp_store_release(&info->is_active, 0); > do_unmask(info, EVT_MASK_REASON_EOI_PENDING); > } > > @@ -809,13 +811,15 @@ static void pirq_query_unmask(int irq) > > static void eoi_pirq(struct irq_data *data) > { > - evtchn_port_t evtchn = evtchn_from_irq(data->irq); > + struct irq_info *info = info_for_irq(data->irq); > + evtchn_port_t evtchn = info ? info->evtchn : 0; > struct physdev_eoi eoi = { .irq = pirq_from_irq(data->irq) }; > int rc = 0; > > if (!VALID_EVTCHN(evtchn)) > return; > > + smp_store_release(&info->is_active, 0);
Would you mind to explain why you are using the release semantics?
It is also not clear to me if there are any expected ordering between clearing is_active and clearing the pending bit.
> clear_evtchn(evtchn);
The 2 lines here seems to be a common pattern in this patch. So I would suggest to create a new helper.
> > if (pirq_needs_eoi(data->irq)) { > @@ -1640,6 +1644,8 @@ void handle_irq_for_port(evtchn_port_t port, struct evtchn_loop_ctrl *ctrl) > } > > info = info_for_irq(irq); > + if (xchg_acquire(&info->is_active, 1)) > + return; > > if (ctrl->defer_eoi) { > info->eoi_cpu = smp_processor_id(); > @@ -1823,11 +1829,13 @@ static void disable_dynirq(struct irq_data *data) > > static void ack_dynirq(struct irq_data *data) > { > - evtchn_port_t evtchn = evtchn_from_irq(data->irq); > + struct irq_info *info = info_for_irq(data->irq); > + evtchn_port_t evtchn = info ? info->evtchn : 0; > > if (!VALID_EVTCHN(evtchn)) > return; > > + smp_store_release(&info->is_active, 0); > clear_evtchn(evtchn); > } > > @@ -1969,10 +1977,13 @@ static void restore_cpu_ipis(unsigned int cpu) > /* Clear an irq's pending state, in preparation for polling on it */ > void xen_clear_irq_pending(int irq) > { > - evtchn_port_t evtchn = evtchn_from_irq(irq); > + struct irq_info *info = info_for_irq(irq); > + evtchn_port_t evtchn = info ? info->evtchn : 0; > > - if (VALID_EVTCHN(evtchn)) > + if (VALID_EVTCHN(evtchn)) { > + smp_store_release(&info->is_active, 0); > clear_evtchn(evtchn); > + } > } > EXPORT_SYMBOL(xen_clear_irq_pending); > void xen_set_irq_pending(int irq) >
-- Julien Grall
| |