Merge tag 'trace-fixes-v3.10-rc3-v3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:
 "This contains 4 fixes.

  The first two fix the case where full RCU debugging is enabled,
  enabling function tracing causes a live lock of the system.  This is
  due to the added debug checks in rcu_dereference_raw() that is used by
  the function tracer.  These checks are also traced by the function
  tracer as well as cause enough overhead to the function tracer to slow
  down the system enough that the time to finish an interrupt can take
  longer than when the next interrupt is triggered, causing a live lock
  from the timer interrupt.

  Talking this over with Paul McKenney, we came up with a fix that adds
  a new rcu_dereference_raw_notrace() that does not perform these added
  checks, and let the function tracer use that.

  The third commit fixes a failed compile when branch tracing is
  enabled, due to the conversion of the trace_test_buffer() selftest
  that the branch trace wasn't converted for.

  The forth patch fixes a bug caught by the RCU lockdep code where a
  rcu_read_lock() is performed when rcu is disabled (either going to or
  from idle, or user space).  This happened on the irqsoff tracer as it
  calls task_uid().  The fix here was to use current_uid() when possible
  that doesn't use rcu locking.  Which luckily, is always used when
  irqsoff calls this code."

* tag 'trace-fixes-v3.10-rc3-v3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  tracing: Use current_uid() for critical time tracing
  tracing: Fix bad parameter passed in branch selftest
  ftrace: Use the rcu _notrace variants for rcu_dereference_raw() and friends
  rcu: Add _notrace variation of rcu_dereference_raw() and hlist_for_each_entry_rcu()

1 files changed, 9 insertions, 1 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 4d79485b3237..1a41023a1f88 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -843,7 +843,15 @@ __update_max_tr(struct trace_array *tr, struct task_struct *tsk, int cpu)
 
 	memcpy(max_data->comm, tsk->comm, TASK_COMM_LEN);
 	max_data->pid = tsk->pid;
-	max_data->uid = task_uid(tsk);
+	/*
+	 * If tsk == current, then use current_uid(), as that does not use
+	 * RCU. The irq tracer can be called out of RCU scope.
+	 */
+	if (tsk == current)
+		max_data->uid = current_uid();
+	else
+		max_data->uid = task_uid(tsk);
+
 	max_data->nice = tsk->static_prio - 20 - MAX_RT_PRIO;
 	max_data->policy = tsk->policy;
 	max_data->rt_priority = tsk->rt_priority;