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SubjectRe: [PATCH v2 1/1] ftrace: do not update max buffer with no users

* Steven Rostedt <rostedt@goodmis.org> wrote:

> Impact: only use max latency buffer when a user is configured
>
> Pekka reported a bug with the resizing of the buffers when only the
> MMIO tracer was configured. The issue was, to save memory, the max
> latency trace buffer was only initialized if a tracer that uses it
> is configured in.
>
> What happened was that the max latency buffer was never initialized
> when only the MMIO tracer was configurued. The MMIO tracer does not
> use the max tracer, which kept it from being initialized. But the
> resize code still tried to resize the max latency buffers, but
> because they were never allocated, the resize code was passed a NULL
> pointer.
>
> This patch checks if the max tracer is NULL before resizing it. It
> also hides the modification functions of the max tracer behind the
> TRACER_MAX_TRACE config.
>
> Reported-by: Pekka Paalanen <pq@iki.fi>
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> ---
> kernel/trace/trace.c | 171 ++++++++++++++++++++++++++------------------------
> 1 files changed, 88 insertions(+), 83 deletions(-)

This is _way_ too much churn for .28, we need a much simpler solution.

Ingo


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