From 229664bee6126e01f8662976a5fe2e79813b77c8 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Mon, 17 Mar 2008 16:37:20 -0700 Subject: [PATCH] xen: short-cut for recursive event handling If an event comes in while events are currently being processed, then just increment the counter and have the outer event loop reprocess the pending events. This prevents unbounded recursion on heavy event loads (of course massive event storms will cause infinite loops). Signed-off-by: Jeremy Fitzhardinge Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner --- arch/x86/xen/events.c | 46 ++++++++++++++++++++++++++++--------------- 1 file changed, 30 insertions(+), 16 deletions(-) diff --git a/arch/x86/xen/events.c b/arch/x86/xen/events.c index f73b53bd65b7..85bac298b3cb 100644 --- a/arch/x86/xen/events.c +++ b/arch/x86/xen/events.c @@ -517,29 +517,43 @@ void xen_evtchn_do_upcall(struct pt_regs *regs) int cpu = get_cpu(); struct shared_info *s = HYPERVISOR_shared_info; struct vcpu_info *vcpu_info = __get_cpu_var(xen_vcpu); - unsigned long pending_words; + static DEFINE_PER_CPU(unsigned, nesting_count); + unsigned count; - vcpu_info->evtchn_upcall_pending = 0; + do { + unsigned long pending_words; - /* NB. No need for a barrier here -- XCHG is a barrier on x86. */ - pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0); - while (pending_words != 0) { - unsigned long pending_bits; - int word_idx = __ffs(pending_words); - pending_words &= ~(1UL << word_idx); + vcpu_info->evtchn_upcall_pending = 0; - while ((pending_bits = active_evtchns(cpu, s, word_idx)) != 0) { - int bit_idx = __ffs(pending_bits); - int port = (word_idx * BITS_PER_LONG) + bit_idx; - int irq = evtchn_to_irq[port]; + if (__get_cpu_var(nesting_count)++) + goto out; - if (irq != -1) { - regs->orig_ax = ~irq; - do_IRQ(regs); + /* NB. No need for a barrier here -- XCHG is a barrier on x86. */ + pending_words = xchg(&vcpu_info->evtchn_pending_sel, 0); + while (pending_words != 0) { + unsigned long pending_bits; + int word_idx = __ffs(pending_words); + pending_words &= ~(1UL << word_idx); + + while ((pending_bits = active_evtchns(cpu, s, word_idx)) != 0) { + int bit_idx = __ffs(pending_bits); + int port = (word_idx * BITS_PER_LONG) + bit_idx; + int irq = evtchn_to_irq[port]; + + if (irq != -1) { + regs->orig_ax = ~irq; + do_IRQ(regs); + } } } - } + BUG_ON(!irqs_disabled()); + + count = __get_cpu_var(nesting_count); + __get_cpu_var(nesting_count) = 0; + } while(count != 1); + +out: put_cpu(); } -- 2.39.2