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xen: short-cut for recursive event handling

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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 <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Jeremy Fitzhardinge 2008-03-17 16:37:20 -07:00 committed by Ingo Molnar
parent ee8fa1c67f
commit 229664bee6
1 changed files with 30 additions and 16 deletions
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46
arch/x86/xen/events.c
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@ -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();
}