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.
ring-buffer: Do not poll non allocated cpu buffers
The tracing infrastructure sets up for possible CPUs, but it uses
the ring buffer polling, it is possible to call the ring buffer
polling code with a CPU that hasn't been allocated. This will cause
a kernel oops when it access a ring buffer cpu buffer that is part
of the possible cpus but hasn't been allocated yet as the CPU has never
been online.
Reported-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Tested-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
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