linux-kernel - Re: [PATCH] ring-buffer: Allow for rescheduling when removing pages

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Message-ID: <CAL26m8+C3tPJLy38i4LajM1_9B+x_AOOvUTot-VUkpHTZfFKmA@mail.gmail.com>
Date:   Mon, 17 Sep 2018 13:53:05 -0700
From:   Vaibhav Nagarnaik <vnagarnaik@...gle.com>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Jason Behmer <jbehmer@...gle.com>
Subject: Re: [PATCH] ring-buffer: Allow for rescheduling when removing pages

Hi Steven,

Does the patch look good? Can this be picked up in the next rc?

Vaibhav

On Fri, Sep 7, 2018 at 3:31 PM Vaibhav Nagarnaik <vnagarnaik@...gle.com> wrote:
>
> When reducing ring buffer size, pages are removed by scheduling a work
> item on each CPU for the corresponding CPU ring buffer. After the pages
> are removed from ring buffer linked list, the pages are free()d in a
> tight loop. The loop does not give up CPU until all pages are removed.
> In a worst case behavior, when lot of pages are to be freed, it can
> cause system stall.
>
> After the pages are removed from the list, the free() can happen while
> the work is rescheduled. Call cond_resched() in the loop to prevent the
> system hangup.
>
> Reported-by: Jason Behmer <jbehmer@...gle.com>
> Signed-off-by: Vaibhav Nagarnaik <vnagarnaik@...gle.com>
> ---
>  kernel/trace/ring_buffer.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 1d92d4a982fd..65bd4616220d 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -1546,6 +1546,8 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
>         tmp_iter_page = first_page;
>
>         do {
> +               cond_resched();
> +
>                 to_remove_page = tmp_iter_page;
>                 rb_inc_page(cpu_buffer, &tmp_iter_page);
>
> --
> 2.19.0.rc2.392.g5ba43deb5a-goog
>

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