linux-kernel - Re: [PATCH] ring-buffer: use atomic_[set|clear]

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Date:	Wed, 15 Oct 2014 15:08:40 -0400
From:	Patrick Palka <patrick@...cs.ath.cx>
To:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:	Patrick Palka <patrick@...cs.ath.cx>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] ring-buffer: use atomic_[set|clear]_mask in place of a
 cmpxchg loop

On Wed, Oct 15, 2014 at 9:41 AM, Patrick Palka <patrick@...cs.ath.cx> wrote:
> Instead of open-coding the equivalent cmpxchg loop we can just use
> atomic_set_mask and atomic_clear_mask to atomically OR or AND
> the value in &buffer->record_disabled.
>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Signed-off-by: Patrick Palka <patrick@...cs.ath.cx>
> ---
>
> NB: I have only tested this patch on x86_64 by booting with
> CONFIG_RING_BUFFER_STARTUP_TEST=y.
>
>  kernel/trace/ring_buffer.c | 16 ++--------------
>  1 file changed, 2 insertions(+), 14 deletions(-)
>
> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
> index 2d75c94..e15ce2a 100644
> --- a/kernel/trace/ring_buffer.c
> +++ b/kernel/trace/ring_buffer.c
> @@ -3050,13 +3050,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
>   */
>  void ring_buffer_record_off(struct ring_buffer *buffer)
>  {
> -       unsigned int rd;
> -       unsigned int new_rd;
> -
> -       do {
> -               rd = atomic_read(&buffer->record_disabled);
> -               new_rd = rd | RB_BUFFER_OFF;
> -       } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
> +       atomic_set_mask(RB_BUFFER_OFF, &buffer->record_disabled);
>  }
>  EXPORT_SYMBOL_GPL(ring_buffer_record_off);
>
> @@ -3073,13 +3067,7 @@ EXPORT_SYMBOL_GPL(ring_buffer_record_off);
>   */
>  void ring_buffer_record_on(struct ring_buffer *buffer)
>  {
> -       unsigned int rd;
> -       unsigned int new_rd;
> -
> -       do {
> -               rd = atomic_read(&buffer->record_disabled);
> -               new_rd = rd & ~RB_BUFFER_OFF;
> -       } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
> +       atomic_clear_mask(RB_BUFFER_OFF, &buffer->record_disabled);
>  }
>  EXPORT_SYMBOL_GPL(ring_buffer_record_on);
>
> --
> 2.1.2.443.g670a3c1
>

It just occurred to me that atomic_clear_mask and atomic_set_mask
expect to take an int *, not an atomic_t *, so this patch is bogus...
Sorry for the noise.
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