Merge tag 'trace-v4.2-rc1-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/roste...

Pull tracing fix from Steven Rostedt:
 "Fengguang Wu discovered a crash that happened to be because of the
  branch tracer (traces unlikely and likely branches) when enabled with
  certain debug options.

  What happened was that various debug options like lockdep and
  DEBUG_PREEMPT can cause parts of the branch tracer to recurse outside
  its recursion protection.  In fact, part of its recursion protection
  used these features that caused the lockup.  This cleans up the code a
  little and makes the recursion protection a bit more robust"

* tag 'trace-v4.2-rc1-fix' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Have branch tracer use recursive field of task struct

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index f060716b02ae25b45494b0f350df6fe2fc0f369b..74bde81601a902759e5714b04a5a987ddbde2d15 100644 (file)
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -444,6 +444,7 @@ enum {
 
        TRACE_CONTROL_BIT,
 
+       TRACE_BRANCH_BIT,
 /*
  * Abuse of the trace_recursion.
  * As we need a way to maintain state if we are tracing the function

diff --git a/kernel/trace/trace_branch.c b/kernel/trace/trace_branch.c
index a87b43f49eb448afa3f1cc2bc44763d71f06dd52..e2e12ad3186f440f7841819a9f260509d5afde43 100644 (file)
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -36,9 +36,12 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
        struct trace_branch *entry;
        struct ring_buffer *buffer;
        unsigned long flags;
-       int cpu, pc;
+       int pc;
        const char *p;
 
+       if (current->trace_recursion & TRACE_BRANCH_BIT)
+               return;
+
        /*
         * I would love to save just the ftrace_likely_data pointer, but
         * this code can also be used by modules. Ugly things can happen
@@ -49,10 +52,10 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
        if (unlikely(!tr))
                return;
 
-       local_irq_save(flags);
-       cpu = raw_smp_processor_id();
-       data = per_cpu_ptr(tr->trace_buffer.data, cpu);
-       if (atomic_inc_return(&data->disabled) != 1)
+       raw_local_irq_save(flags);
+       current->trace_recursion |= TRACE_BRANCH_BIT;
+       data = this_cpu_ptr(tr->trace_buffer.data);
+       if (atomic_read(&data->disabled))
                goto out;
 
        pc = preempt_count();
@@ -81,8 +84,8 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
                __buffer_unlock_commit(buffer, event);
 
  out:
-       atomic_dec(&data->disabled);
-       local_irq_restore(flags);
+       current->trace_recursion &= ~TRACE_BRANCH_BIT;
+       raw_local_irq_restore(flags);
 }
 
 static inline