Merge branch 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-fixes-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  generic-ipi: use per cpu data for single cpu ipi calls
  cpumask: convert lib/smp_processor_id to new cpumask ops
  signals, debug: fix BUG: using smp_processor_id() in preemptible code in print_fatal_signal()

2 files changed, 35 insertions, 3 deletions

diff --git a/kernel/signal.c b/kernel/signal.c
index e73759783dc8..b6b36768b758 100644
--- a/kernel/signal.c
+++ b/kernel/signal.c
@@ -909,7 +909,9 @@ static void print_fatal_signal(struct pt_regs *regs, int signr)
         }
 #endif
         printk("\n");
+        preempt_disable();
         show_regs(regs);
+        preempt_enable();
 }
 
 static int __init setup_print_fatal_signals(char *str)
diff --git a/kernel/smp.c b/kernel/smp.c
index 5cfa0e5e3e88..bbedbb7efe32 100644
--- a/kernel/smp.c
+++ b/kernel/smp.c
@@ -18,6 +18,7 @@ __cacheline_aligned_in_smp DEFINE_SPINLOCK(call_function_lock);
 enum {
         CSD_FLAG_WAIT           = 0x01,
         CSD_FLAG_ALLOC          = 0x02,
+        CSD_FLAG_LOCK           = 0x04,
 };
 
 struct call_function_data {
@@ -186,6 +187,9 @@ void generic_smp_call_function_single_interrupt(void)
                         if (data_flags & CSD_FLAG_WAIT) {
                                 smp_wmb();
                                 data->flags &= ~CSD_FLAG_WAIT;
+                        } else if (data_flags & CSD_FLAG_LOCK) {
+                                smp_wmb();
+                                data->flags &= ~CSD_FLAG_LOCK;
                         } else if (data_flags & CSD_FLAG_ALLOC)
                                 kfree(data);
                 }
@@ -196,6 +200,8 @@ void generic_smp_call_function_single_interrupt(void)
         }
 }
 
+static DEFINE_PER_CPU(struct call_single_data, csd_data);
+
 /*
  * smp_call_function_single - Run a function on a specific CPU
  * @func: The function to run. This must be fast and non-blocking.
@@ -224,14 +230,38 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
                 func(info);
                 local_irq_restore(flags);
         } else if ((unsigned)cpu < nr_cpu_ids && cpu_online(cpu)) {
-                struct call_single_data *data = NULL;
+                struct call_single_data *data;
 
                 if (!wait) {
+                        /*
+                         * We are calling a function on a single CPU
+                         * and we are not going to wait for it to finish.
+                         * We first try to allocate the data, but if we
+                         * fail, we fall back to use a per cpu data to pass
+                         * the information to that CPU. Since all callers
+                         * of this code will use the same data, we must
+                         * synchronize the callers to prevent a new caller
+                         * from corrupting the data before the callee
+                         * can access it.
+                         *
+                         * The CSD_FLAG_LOCK is used to let us know when
+                         * the IPI handler is done with the data.
+                         * The first caller will set it, and the callee
+                         * will clear it. The next caller must wait for
+                         * it to clear before we set it again. This
+                         * will make sure the callee is done with the
+                         * data before a new caller will use it.
+                         */
                         data = kmalloc(sizeof(*data), GFP_ATOMIC);
                         if (data)
                                 data->flags = CSD_FLAG_ALLOC;
-                }
-                if (!data) {
+                        else {
+                                data = &per_cpu(csd_data, me);
+                                while (data->flags & CSD_FLAG_LOCK)
+                                        cpu_relax();
+                                data->flags = CSD_FLAG_LOCK;
+                        }
+                } else {
                         data = &d;
                         data->flags = CSD_FLAG_WAIT;
                 }