# HG changeset patch
# User kfraser@xxxxxxxxxxxxxxxxxxxxx
# Date 1166612996 0
# Node ID 3a28be71b667a336c7589cbb7056841f9e42df6a
# Parent 516e4faac066437af4b41014da831d2ad8ae0493
[LINUX] Disallow nested event delivery.
This eliminates the risk of overflowing the kernel stack and is a
reasonable policy given that we have no concept of priorities among
event sources.
Signed-off-by: Keir Fraser <keir@xxxxxxxxxxxxx>
---
linux-2.6-xen-sparse/drivers/xen/core/evtchn.c | 51 +++++++++++++++----------
1 files changed, 32 insertions(+), 19 deletions(-)
diff -r 516e4faac066 -r 3a28be71b667
linux-2.6-xen-sparse/drivers/xen/core/evtchn.c
--- a/linux-2.6-xen-sparse/drivers/xen/core/evtchn.c Wed Dec 20 10:41:33
2006 +0000
+++ b/linux-2.6-xen-sparse/drivers/xen/core/evtchn.c Wed Dec 20 11:09:56
2006 +0000
@@ -208,38 +208,51 @@ void force_evtchn_callback(void)
/* Not a GPL symbol: used in ubiquitous macros, so too restrictive. */
EXPORT_SYMBOL(force_evtchn_callback);
+static DEFINE_PER_CPU(unsigned int, upcall_count) = { 0 };
+
/* NB. Interrupts are disabled on entry. */
asmlinkage void evtchn_do_upcall(struct pt_regs *regs)
{
unsigned long l1, l2;
- unsigned int l1i, l2i, port;
+ unsigned int l1i, l2i, port, count;
int irq, cpu = smp_processor_id();
shared_info_t *s = HYPERVISOR_shared_info;
vcpu_info_t *vcpu_info = &s->vcpu_info[cpu];
- vcpu_info->evtchn_upcall_pending = 0;
+ do {
+ /* Avoid a callback storm when we reenable delivery. */
+ vcpu_info->evtchn_upcall_pending = 0;
+
+ /* Nested invocations bail immediately. */
+ if (unlikely(per_cpu(upcall_count, cpu)++))
+ return;
#ifndef CONFIG_X86 /* No need for a barrier -- XCHG is a barrier on x86. */
- /* Clear master pending flag /before/ clearing selector flag. */
- rmb();
+ /* Clear master flag /before/ clearing selector flag. */
+ rmb();
#endif
- l1 = xchg(&vcpu_info->evtchn_pending_sel, 0);
- while (l1 != 0) {
- l1i = __ffs(l1);
- l1 &= ~(1UL << l1i);
-
- while ((l2 = active_evtchns(cpu, s, l1i)) != 0) {
- l2i = __ffs(l2);
-
- port = (l1i * BITS_PER_LONG) + l2i;
- if ((irq = evtchn_to_irq[port]) != -1)
- do_IRQ(irq, regs);
- else {
- exit_idle();
- evtchn_device_upcall(port);
+ l1 = xchg(&vcpu_info->evtchn_pending_sel, 0);
+ while (l1 != 0) {
+ l1i = __ffs(l1);
+ l1 &= ~(1UL << l1i);
+
+ while ((l2 = active_evtchns(cpu, s, l1i)) != 0) {
+ l2i = __ffs(l2);
+
+ port = (l1i * BITS_PER_LONG) + l2i;
+ if ((irq = evtchn_to_irq[port]) != -1)
+ do_IRQ(irq, regs);
+ else {
+ exit_idle();
+ evtchn_device_upcall(port);
+ }
}
}
- }
+
+ /* If there were nested callbacks then we have more to do. */
+ count = per_cpu(upcall_count, cpu);
+ per_cpu(upcall_count, cpu) = 0;
+ } while (unlikely(count != 1));
}
static int find_unbound_irq(void)
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