Impact: stop ftrace_special from recursion

The ftrace_special is used to help debug areas of the kernel.
Because of this, if it is put in certain locations, the fact that
it allows recursion can become a problem if the kernel developer
using does not realize that.

This patch changes ftrace_special to not allow recursion into itself
to make it more robust.

It also changes from preempt disable interrupts disable to prevent
any loss of trace entries.

Signed-off-by: Steven Rostedt
---
kernel/trace/trace.c | 8 +++++---
1 files changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5d3dd8a..50f3237 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -960,6 +960,7 @@ ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3)
{
struct trace_array *tr = &global_trace;
struct trace_array_cpu *data;
+ unsigned long flags;
int cpu;
int pc;

@@ -967,14 +968,15 @@ ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3)
return;

pc = preempt_count();
- preempt_disable_notrace();
+ local_irq_save(flags);
cpu = raw_smp_processor_id();
data = tr->data[cpu];

- if (likely(!atomic_read(&data->disabled)))
+ if (likely(atomic_inc_return(&data->disabled) == 1))
ftrace_trace_special(tr, data, arg1, arg2, arg3, pc);

- preempt_enable_notrace();
+ atomic_dec(&data->disabled);
+ local_irq_restore(flags);
}

#ifdef CONFIG_FUNCTION_TRACER
--
1.5.6.5

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