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SubjectRe: [PATCH 1/4] perf/ring_buffer: Fix exposing a temporarily decreased data_head.

* Peter Zijlstra <peterz@infradead.org> wrote:

> In perf_output_put_handle(), an IRQ/NMI can happen in below location and
> write records to the same ring buffer:
> ...
> local_dec_and_test(&rb->nest)
> ... <-- an IRQ/NMI can happen here
> rb->user_page->data_head = head;
> ...
>
> In this case, a value A is written to data_head in the IRQ, then a value
> B is written to data_head after the IRQ. And A > B. As a result,
> data_head is temporarily decreased from A to B. And a reader may see
> data_head < data_tail if it read the buffer frequently enough, which
> creates unexpected behaviors.
>
> This can be fixed by moving dec(&rb->nest) to after updating data_head,
> which prevents the IRQ/NMI above from updating data_head.
>
> Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Jiri Olsa <jolsa@redhat.com>
> Cc: Namhyung Kim <namhyung@kernel.org>
> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> Fixes: ef60777c9abd ("perf: Optimize the perf_output() path by removing IRQ-disables")
> Signed-off-by: Yabin Cui <yabinc@google.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Link: https://lkml.kernel.org/r/20190516184010.167903-1-yabinc@google.com

So these are missing a bunch of:

From: Yabin Cui <yabinc@google.com>

lines, right?

Thanks,

Ingo

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