ftrace: use raw_smp_processor_id for mcount functions

Due to debug hooks in the kernel that can change the way smp_processor_id
works, use raw_smp_processor_id in mcount called functions (namely
ftrace_record_ip). Currently we annotate most debug functions from calling
mcount, but we should not rely on that to prevent kernel lockups.

This patch uses the raw_smp_processor_id to prevent a recusive crash
that can happen if a debug hook in smp_processor_id calls mcount.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 11 insertions, 4 deletions

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 40f64f7cd850..af5ad8949abb 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -267,6 +267,7 @@ ftrace_record_ip(unsigned long ip)
         unsigned long key;
         int resched;
         int atomic;
+        int cpu;
 
         if (!ftrace_enabled || ftrace_disabled)
                 return;
@@ -274,9 +275,15 @@ ftrace_record_ip(unsigned long ip)
         resched = need_resched();
         preempt_disable_notrace();
 
-        /* We simply need to protect against recursion */
-        __get_cpu_var(ftrace_shutdown_disable_cpu)++;
-        if (__get_cpu_var(ftrace_shutdown_disable_cpu) != 1)
+        /*
+         * We simply need to protect against recursion.
+         * Use the the raw version of smp_processor_id and not
+         * __get_cpu_var which can call debug hooks that can
+         * cause a recursive crash here.
+         */
+        cpu = raw_smp_processor_id();
+        per_cpu(ftrace_shutdown_disable_cpu, cpu)++;
+        if (per_cpu(ftrace_shutdown_disable_cpu, cpu) != 1)
                 goto out;
 
         if (unlikely(ftrace_record_suspend))
@@ -317,7 +324,7 @@ ftrace_record_ip(unsigned long ip)
  out_unlock:
         spin_unlock_irqrestore(&ftrace_shutdown_lock, flags);
  out:
-        __get_cpu_var(ftrace_shutdown_disable_cpu)--;
+        per_cpu(ftrace_shutdown_disable_cpu, cpu)--;
 
         /* prevent recursion with scheduler */
         if (resched)