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

* 'tracing-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip: (28 commits)
  ftrace: Add function names to dangling } in function graph tracer
  tracing: Simplify memory recycle of trace_define_field
  tracing: Remove unnecessary variable in print_graph_return
  tracing: Fix typo of info text in trace_kprobe.c
  tracing: Fix typo in prof_sysexit_enable()
  tracing: Remove CONFIG_TRACE_POWER from kernel config
  tracing: Fix ftrace_event_call alignment for use with gcc 4.5
  ftrace: Remove memory barriers from NMI code when not needed
  tracing/kprobes: Add short documentation for HAVE_REGS_AND_STACK_ACCESS_API
  s390: Add pt_regs register and stack access API
  tracing/kprobes: Make Kconfig dependencies generic
  tracing: Unify arch_syscall_addr() implementations
  tracing: Add notrace to TRACE_EVENT implementation functions
  ftrace: Allow to remove a single function from function graph filter
  tracing: Add correct/incorrect to sort keys for branch annotation output
  tracing: Simplify test for function_graph tracing start point
  tracing: Drop the tr check from the graph tracing path
  tracing: Add stack dump to trace_printk if stacktrace option is set
  tracing: Use appropriate perl constructs in recordmcount.pl
  tracing: optimize recordmcount.pl for offsets-handling
  ...

3 files changed, 29 insertions, 10 deletions

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index eb4092568f9e..0896008f7509 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -45,6 +45,7 @@ config X86
         select HAVE_GENERIC_DMA_COHERENT if X86_32
         select HAVE_EFFICIENT_UNALIGNED_ACCESS
         select USER_STACKTRACE_SUPPORT
+        select HAVE_REGS_AND_STACK_ACCESS_API
         select HAVE_DMA_API_DEBUG
         select HAVE_KERNEL_GZIP
         select HAVE_KERNEL_BZIP2
diff --git a/arch/x86/include/asm/syscall.h b/arch/x86/include/asm/syscall.h
index 8d33bc5462d1..c4a348f7bd43 100644
--- a/arch/x86/include/asm/syscall.h
+++ b/arch/x86/include/asm/syscall.h
@@ -16,6 +16,8 @@
 #include <linux/sched.h>
 #include <linux/err.h>
 
+extern const unsigned long sys_call_table[];
+
 /*
  * Only the low 32 bits of orig_ax are meaningful, so we return int.
  * This importantly ignores the high bits on 64-bit, so comparisons
diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c
index 309689245431..cd37469b54ee 100644
--- a/arch/x86/kernel/ftrace.c
+++ b/arch/x86/kernel/ftrace.c
@@ -30,14 +30,32 @@
 
 #ifdef CONFIG_DYNAMIC_FTRACE
 
+/*
+ * modifying_code is set to notify NMIs that they need to use
+ * memory barriers when entering or exiting. But we don't want
+ * to burden NMIs with unnecessary memory barriers when code
+ * modification is not being done (which is most of the time).
+ *
+ * A mutex is already held when ftrace_arch_code_modify_prepare
+ * and post_process are called. No locks need to be taken here.
+ *
+ * Stop machine will make sure currently running NMIs are done
+ * and new NMIs will see the updated variable before we need
+ * to worry about NMIs doing memory barriers.
+ */
+static int modifying_code __read_mostly;
+static DEFINE_PER_CPU(int, save_modifying_code);
+
 int ftrace_arch_code_modify_prepare(void)
 {
         set_kernel_text_rw();
+        modifying_code = 1;
         return 0;
 }
 
 int ftrace_arch_code_modify_post_process(void)
 {
+        modifying_code = 0;
         set_kernel_text_ro();
         return 0;
 }
@@ -149,6 +167,11 @@ static void ftrace_mod_code(void)
 
 void ftrace_nmi_enter(void)
 {
+        __get_cpu_var(save_modifying_code) = modifying_code;
+
+        if (!__get_cpu_var(save_modifying_code))
+                return;
+
         if (atomic_inc_return(&nmi_running) & MOD_CODE_WRITE_FLAG) {
                 smp_rmb();
                 ftrace_mod_code();
@@ -160,6 +183,9 @@ void ftrace_nmi_enter(void)
 
 void ftrace_nmi_exit(void)
 {
+        if (!__get_cpu_var(save_modifying_code))
+                return;
+
         /* Finish all executions before clearing nmi_running */
         smp_mb();
         atomic_dec(&nmi_running);
@@ -484,13 +510,3 @@ void prepare_ftrace_return(unsigned long *parent, unsigned long self_addr,
         }
 }
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */
-
-#ifdef CONFIG_FTRACE_SYSCALLS
-
-extern unsigned long *sys_call_table;
-
-unsigned long __init arch_syscall_addr(int nr)
-{
-        return (unsigned long)(&sys_call_table)[nr];
-}
-#endif