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RE: [PATCH] staging: unisys: visorbus: visorchannel: Refactor locking code to be statically deterministic.

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On Wednesday, October 19, 2016 7:31 AM, Cathal Mullaney wrote:
> This patch makes locking in visorchannel_signalempty statically deterministic.
> As a result this patch fixes the sparse warning:
> Context imbalance in 'visorchannel_signalempty' - different lock contexts for
> basic block.
> 
> The logic of the locking code doesn't change but the layout of the original
> code is "frowned upon"
> according to mails on sparse context checking.
> Refactoring removes the warning and makes the code more readable.
> 
> Signed-off-by: Cathal Mullaney <chuckleberryfinn@gmail.com>
> ---
>  drivers/staging/unisys/visorbus/visorchannel.c | 26 +++++++++++++++++---
> ------
>  1 file changed, 17 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/staging/unisys/visorbus/visorchannel.c
> b/drivers/staging/unisys/visorbus/visorchannel.c
> index a1381eb..1eea5d8 100644
> --- a/drivers/staging/unisys/visorbus/visorchannel.c
> +++ b/drivers/staging/unisys/visorbus/visorchannel.c
> @@ -300,22 +300,30 @@
> ---
>  bool
>  visorchannel_signalempty(struct visorchannel *channel, u32 queue)
>  {
>  	unsigned long flags = 0;
> -	struct signal_queue_header sig_hdr;
>  	bool rc = false;

It appears as if you no longer need to initialize 'rc' above.

Although this is NOT caused by your patch, it also looks like 'flags'
is being unnecessarily initialized.  You may want to fix that too
while you're in the neighborhood.

(Kernel folks seem to frown on unnecessary variable initializations.)

> 
> -	if (channel->needs_lock)
> -		spin_lock_irqsave(&channel->remove_lock, flags);
> +	if (!channel->needs_lock)
> +		return queue_empty(channel, queue);
> 
> -	if (sig_read_header(channel, queue, &sig_hdr))
> -		rc = true;
> -	if (sig_hdr.head == sig_hdr.tail)
> -		rc = true;
> -	if (channel->needs_lock)
> -		spin_unlock_irqrestore(&channel->remove_lock, flags);
> +	spin_lock_irqsave(&channel->remove_lock, flags);
> +	rc = queue_empty(channel, queue);
> +	spin_unlock_irqrestore(&channel->remove_lock, flags);
> 
>  	return rc;
>  }
> --
> 2.7.4

Besides that, your patch looks good to me.  Thanks.

- Tim Sell

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[PATCH] staging: unisys: visorbus: visorchannel: Refactor locking code to be statically deterministic. Cathal Mullaney <chuckleberryfinn@gmail.com> - 2016-10-19 17:50 +0200
  RE: [PATCH] staging: unisys: visorbus: visorchannel: Refactor locking  code to be statically deterministic. "Sell, Timothy C" <Timothy.Sell@unisys.com> - 2016-10-19 22:40 +0200
    Re: [PATCH] staging: unisys: visorbus: visorchannel: Refactor  locking code to be statically deterministic. Chuckleberryfinn <chuckleberryfinn@gmail.com> - 2016-10-20 00:00 +0200
  [PATCH v2] staging: unisys: visorbus: visorchannel: Refactor locking code to be statically deterministic. Cathal Mullaney <chuckleberryfinn@gmail.com> - 2016-10-19 23:50 +0200
    RE: [PATCH v2] staging: unisys: visorbus: visorchannel: Refactor  locking code to be statically deterministic. "Kershner, David A" <David.Kershner@unisys.com> - 2016-10-20 04:40 +0200
      RE: [PATCH v2] staging: unisys: visorbus: visorchannel: Refactor  locking code to be statically deterministic. "Sell, Timothy C" <Timothy.Sell@unisys.com> - 2016-10-20 05:20 +0200

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