Commit e3bf756e authored May 28, 2013 by Linus Torvalds

Merge tag 'trace-fixes-v3.10-rc3' of...

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

Pull tracing fixes from Steven Rostedt:
"Two more fixes:

The first one was reported by Mauro Carvalho Chehab, where if a poll()
is done against a trace buffer for a CPU that has never been online,
it will crash the kernel, as buffers are only created when a CPU comes
on line, but the trace files are for all possible CPUs.

This fix is to check if the buffer was allocated and if not return
-EINVAL.

That was the simple fix, the real fix is a bit more complex and not
for a -rc release. We could have the files created when the CPUs come
online. That would require some design changes.

The second one was reported by Peter Zijlstra. If the kernel command
line has ftrace=nop, it will lock up the system on boot up. This is
because the new design for 3.10 has the nop tracer bootstrap the
tracing subsystem. When ftrace=<trace> is defined, when a that tracer
is registered, it starts the tracing, but uses the nop tracer to clear
things out. What happened here was that ftrace=nop caused the
registering of nop to start it and use nop before it was initialized.

The only thing nop needs to have done to initialize it is to have the
tracer point its current_tracer structure member to the nop tracer.
Doing that before registering the nop tracer makes everything work."

* tag 'trace-fixes-v3.10-rc3' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
ring-buffer: Do not poll non allocated cpu buffers
tracing: Fix crash when ftrace=nop on the kernel command line

parents 3c48dd49 6721cb60

kernel/trace/ring_buffer.c

+3 −0

Original line number	Diff line number	Diff line
		@@ -620,6 +620,9 @@ int ring_buffer_poll_wait(struct ring_buffer *buffer, int cpu,
		if (cpu == RING_BUFFER_ALL_CPUS)
		work = &buffer->irq_work;
		else {
		if (!cpumask_test_cpu(cpu, buffer->cpumask))
		return -EINVAL;

		cpu_buffer = buffer->buffers[cpu];
		work = &cpu_buffer->irq_work;
		}

kernel/trace/trace.c

+7 −2

Original line number	Diff line number	Diff line
		@@ -6216,10 +6216,15 @@ __init static int tracer_alloc_buffers(void)

		trace_init_cmdlines();

		register_tracer(&nop_trace);

		/*
		* register_tracer() might reference current_trace, so it
		* needs to be set before we register anything. This is
		* just a bootstrap of current_trace anyway.
		*/
		global_trace.current_trace = &nop_trace;

		register_tracer(&nop_trace);

		/* All seems OK, enable tracing */
		tracing_disabled = 0;

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