linux-kernel - Re: [trace] kernel BUG at kernel/sched/core.c:2881!

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Date:	Tue, 7 Jul 2015 11:06:27 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, LKP <lkp@...org>
Subject: Re: [trace] kernel BUG at kernel/sched/core.c:2881!

On Tue, 30 Jun 2015 22:18:03 +0800
Fengguang Wu <fengguang.wu@...el.com> wrote:

> Hi Rostedt,
> 
> FYI, this merge changes kernel crash to some more obvious kernel BUG
> message. If it's still not helpful, I can try bisect the old crash
> or split up the merge and bisect into them.
> 
> git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> 

This has been a bug for some time. Does this fix it?

-- Steve

diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index f060716b02ae..74bde81601a9 100644
--- 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 a87b43f49eb4..720ed604882e 100644
--- a/kernel/trace/trace_branch.c
+++ b/kernel/trace/trace_branch.c
@@ -49,7 +49,11 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
 	if (unlikely(!tr))
 		return;
 
+	if (current->trace_recursion & TRACE_BRANCH_BIT)
+		return;
+
 	local_irq_save(flags);
+	current->trace_recursion |= TRACE_BRANCH_BIT;
 	cpu = raw_smp_processor_id();
 	data = per_cpu_ptr(tr->trace_buffer.data, cpu);
 	if (atomic_inc_return(&data->disabled) != 1)
@@ -82,6 +86,7 @@ probe_likely_condition(struct ftrace_branch_data *f, int val, int expect)
 
  out:
 	atomic_dec(&data->disabled);
+	current->trace_recursion &= ~TRACE_BRANCH_BIT;
 	local_irq_restore(flags);
 }
 
--
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