Module Name: src
Committed By: riastradh
Date: Fri Nov 10 19:24:17 UTC 2017
Modified Files:
src/sys/arch/xen/xen: evtchn.c
Log Message:
Fix theoretical race in xen_evtchn_trymask.
This now matches ioapic_trymask:
- Caller masks CPU interrupts while the PIC's interrupts are unmasked.
- Trymask masks the PIC's interrupts, and tests whether any were
pending that we missed because the CPU interrupts are masked.
==> If there were any pending, trymask unmasks PIC's interrupts and
returns false.
==> If not, interrupts are masked on the PIC and CPU and there were
none pending and trymask returns true.
No functional change right now because cpu_intr_redistribute is
currently disabled on Xen.
ok cherry
To generate a diff of this commit:
cvs rdiff -u -r1.74 -r1.75 src/sys/arch/xen/xen/evtchn.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/arch/xen/xen/evtchn.c
diff -u src/sys/arch/xen/xen/evtchn.c:1.74 src/sys/arch/xen/xen/evtchn.c:1.75
--- src/sys/arch/xen/xen/evtchn.c:1.74 Sat Nov 4 10:26:14 2017
+++ src/sys/arch/xen/xen/evtchn.c Fri Nov 10 19:24:17 2017
@@ -1,4 +1,4 @@
-/* $NetBSD: evtchn.c,v 1.74 2017/11/04 10:26:14 cherry Exp $ */
+/* $NetBSD: evtchn.c,v 1.75 2017/11/10 19:24:17 riastradh Exp $ */
/*
* Copyright (c) 2006 Manuel Bouyer.
@@ -54,7 +54,7 @@
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: evtchn.c,v 1.74 2017/11/04 10:26:14 cherry Exp $");
+__KERNEL_RCSID(0, "$NetBSD: evtchn.c,v 1.75 2017/11/10 19:24:17 riastradh Exp $");
#include "opt_xen.h"
#include "isa.h"
@@ -505,22 +505,39 @@ xen_evtchn_delroute(struct pic *pic, str
xen_atomic_clear_bit(&ci->ci_evtmask[0], evtchn);
}
+/*
+ * xen_evtchn_trymask(pic, pin)
+ *
+ * If there are interrupts pending on the bus-shared pic, return
+ * false. Otherwise, mask interrupts on the bus-shared pic and
+ * return true.
+ */
static bool
xen_evtchn_trymask(struct pic *pic, int pin)
{
- volatile shared_info_t *s = HYPERVISOR_shared_info;
+ volatile struct shared_info *s = HYPERVISOR_shared_info;
+ unsigned long masked __diagused;
- /* Already masked! */
- if (xen_atomic_test_bit(&s->evtchn_mask[0], pin))
- return true;
-
- /* Pending - bail! */
- if (xen_atomic_test_bit(&s->evtchn_pending[0], pin))
+ /* Mask it. */
+ masked = xen_atomic_test_and_set_bit(&s->evtchn_mask[0], pin);
+
+ /*
+ * Caller is responsible for calling trymask only when the
+ * interrupt pin is not masked, and for serializing calls to
+ * trymask.
+ */
+ KASSERT(!masked);
+
+ /*
+ * Check whether there were any interrupts pending when we
+ * masked it. If there were, unmask and abort.
+ */
+ if (xen_atomic_test_bit(&s->evtchn_pending[0], pin)) {
+ xen_atomic_clear_bit(&s->evtchn_mask[0], pin);
return false;
+ }
- /* XXX: There's a race here - anything we can do about this ? */
- /* Mask it */
- xen_atomic_set_bit(&s->evtchn_mask[0], pin);
+ /* Success: masked, not pending. */
return true;
}
