The patch below does not apply to the 4.4-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 3de218ff39b9e3f0d453fe3154f12a174de44b25 Mon Sep 17 00:00:00 2001
From: Juergen Gross jgross@suse.com Date: Wed, 23 Jun 2021 15:09:13 +0200 Subject: [PATCH] xen/events: reset active flag for lateeoi events later
In order to avoid a race condition for user events when changing cpu affinity reset the active flag only when EOI-ing the event.
This is working fine as all user events are lateeoi events. Note that lateeoi_ack_mask_dynirq() is not modified as there is no explicit call to xen_irq_lateeoi() expected later.
Cc: stable@vger.kernel.org Reported-by: Julien Grall julien@xen.org Fixes: b6622798bc50b62 ("xen/events: avoid handling the same event on two cpus at the same time") Tested-by: Julien Grall julien@xen.org Signed-off-by: Juergen Gross jgross@suse.com Reviewed-by: Boris Ostrovsky boris.ostrvsky@oracle.com Link: https://lore.kernel.org/r/20210623130913.9405-1-jgross@suse.com Signed-off-by: Juergen Gross jgross@suse.com
diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c index 7bbfd58958bc..d7e361fb0548 100644 --- a/drivers/xen/events/events_base.c +++ b/drivers/xen/events/events_base.c @@ -642,6 +642,9 @@ static void xen_irq_lateeoi_locked(struct irq_info *info, bool spurious) }
info->eoi_time = 0; + + /* is_active hasn't been reset yet, do it now. */ + smp_store_release(&info->is_active, 0); do_unmask(info, EVT_MASK_REASON_EOI_PENDING); }
@@ -811,6 +814,7 @@ static void xen_evtchn_close(evtchn_port_t port) BUG(); }
+/* Not called for lateeoi events. */ static void event_handler_exit(struct irq_info *info) { smp_store_release(&info->is_active, 0); @@ -1883,7 +1887,12 @@ static void lateeoi_ack_dynirq(struct irq_data *data)
if (VALID_EVTCHN(evtchn)) { do_mask(info, EVT_MASK_REASON_EOI_PENDING); - event_handler_exit(info); + /* + * Don't call event_handler_exit(). + * Need to keep is_active non-zero in order to ignore re-raised + * events after cpu affinity changes while a lateeoi is pending. + */ + clear_evtchn(evtchn); } }