xen: add some debug output for failed multicalls

Multicalls are expected to never fail, and the normal response to a
failed multicall is very terse.  In the interests of better
debuggability, add some more verbose output.  It may be worth turning
this off once it all seems more tested.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
index ce9c4b41f02d..5e6f36f6d876 100644
--- a/arch/x86/xen/multicalls.c
+++ b/arch/x86/xen/multicalls.c
@@ -26,11 +26,16 @@
 
 #include "multicalls.h"
 
+#define MC_DEBUG        1
+
 #define MC_BATCH        32
 #define MC_ARGS         (MC_BATCH * 16 / sizeof(u64))
 
 struct mc_buffer {
         struct multicall_entry entries[MC_BATCH];
+#if MC_DEBUG
+        struct multicall_entry debug[MC_BATCH];
+#endif
         u64 args[MC_ARGS];
         struct callback {
                 void (*fn)(void *);
@@ -56,11 +61,31 @@ void xen_mc_flush(void)
         local_irq_save(flags);
 
         if (b->mcidx) {
+#if MC_DEBUG
+                memcpy(b->debug, b->entries,
+                       b->mcidx * sizeof(struct multicall_entry));
+#endif
+
                 if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
                         BUG();
                 for (i = 0; i < b->mcidx; i++)
                         if (b->entries[i].result < 0)
                                 ret++;
+
+#if MC_DEBUG
+                if (ret) {
+                        printk(KERN_ERR "%d multicall(s) failed: cpu %d\n",
+                               ret, smp_processor_id());
+                        for(i = 0; i < b->mcidx; i++) {
+                                printk("  call %2d/%d: op=%lu arg=[%lx] result=%ld\n",
+                                       i+1, b->mcidx,
+                                       b->debug[i].op,
+                                       b->debug[i].args[0],
+                                       b->entries[i].result);
+                        }
+                }
+#endif
+
                 b->mcidx = 0;
                 b->argidx = 0;
         } else