[PATCH 3/3] xen/events: schedule if the interrupted task is in a preemptible hypercall

[David Vrabel <david.vrabel@citrix.com>]

From: Andrew Cooper <andrew.cooper3@citrix.com>

In evtchn_do_upcall(), if the interrupted task was in a preemptible
hypercall add a conditional schedule point.

This allows tasks in long running preemptible hypercalls to be
descheduled.  Allowing other tasks to run and prevents long running
hypercalls issued via the privcmd driver from triggering soft lockups.

Signed-off-by: Andrew Cooper <andrew.cooper3.citrix.com>
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
---
 drivers/xen/events/events_base.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/drivers/xen/events/events_base.c b/drivers/xen/events/events_base.c
index 4672e00..0b5df37 100644
--- a/drivers/xen/events/events_base.c
+++ b/drivers/xen/events/events_base.c
@@ -1254,6 +1254,12 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
 
 	irq_exit();
 	set_irq_regs(old_regs);
+
+#ifndef CONFIG_PREEMPT
+	if ( __this_cpu_read(xed_nesting_count) == 0
+	     && is_preemptible_hypercall(regs) )
+		_cond_resched();
+#endif
 }
 
 void xen_hvm_evtchn_do_upcall(void)
-- 
1.7.2.5