linux-kernel - Re: [PATCH 1/2 RFC] ath10k: move code out of the parameter list

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Message-ID: <87h9tr4d98.fsf@nemi.mork.no>
Date:	Wed, 11 Mar 2015 19:09:39 +0100
From:	Bjørn Mork <bjorn@...k.no>
To:	Nicholas Mc Guire <hofrat@...dl.org>
Cc:	Kalle Valo <kvalo@....qualcomm.com>, Valdis.Kletnieks@...edu,
	ath10k@...ts.infradead.org, linux-wireless@...r.kernel.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2 RFC] ath10k: move code out of the parameter list

Nicholas Mc Guire <hofrat@...dl.org> writes:

> Putting code into the parameter list of wait_event_timeout() might be 
> legal C-code but not really readable - the "inline" code is simply
> moved into a function and that passed to wait_event_timeout() as the
> condition.
>
> Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
> ---
>
> Thanks to Bjorn Mork <bjorn@...k.no> for clarifying my initial confusion !
>
> Patch was only compile tested with x86_64_defconfig + CONFIG_ATH_CARDS=m,
> CONFIG_ATH10K=m
>
> Patch is against 4.0-rc3 (localversion-next is -next-20150311)
>
>  drivers/net/wireless/ath/ath10k/mac.c |   32 ++++++++++++++++++--------------
>  1 file changed, 18 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath10k/mac.c b/drivers/net/wireless/ath/ath10k/mac.c
> index e8cc19f..7b27d99 100644
> --- a/drivers/net/wireless/ath/ath10k/mac.c
> +++ b/drivers/net/wireless/ath/ath10k/mac.c
> @@ -4463,11 +4463,25 @@ static int ath10k_set_rts_threshold(struct ieee80211_hw *hw, u32 value)
>  	return ret;
>  }
>  
> +static bool check_htt_state(struct ath10k *ar, bool skip)
> +{
> +	bool empty;
> +
> +	spin_lock_bh(&ar->htt.tx_lock);
> +	empty = (ar->htt.num_pending_tx == 0);
> +	spin_unlock_bh(&ar->htt.tx_lock);
> +
> +	skip = (ar->state == ATH10K_STATE_WEDGED) ||
> +		test_bit(ATH10K_FLAG_CRASH_FLUSH,
> +			 &ar->dev_flags);
> +	return (empty || skip);
> +}


There is no value in the "skip" input argument here.  It could just as
well be a local variable.


>  static void ath10k_flush(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
>  			 u32 queues, bool drop)
>  {
>  	struct ath10k *ar = hw->priv;
> -	bool skip;
> +	bool skip = false;
>  	int ret;
>  
>  	/* mac80211 doesn't care if we really xmit queued frames or not
> @@ -4480,19 +4494,9 @@ static void ath10k_flush(struct ieee80211_hw *hw, struct ieee80211_vif *vif,
>  	if (ar->state == ATH10K_STATE_WEDGED)
>  		goto skip;
>  
> -	ret = wait_event_timeout(ar->htt.empty_tx_wq, ({
> -			bool empty;
> -
> -			spin_lock_bh(&ar->htt.tx_lock);
> -			empty = (ar->htt.num_pending_tx == 0);
> -			spin_unlock_bh(&ar->htt.tx_lock);
> -
> -			skip = (ar->state == ATH10K_STATE_WEDGED) ||
> -			       test_bit(ATH10K_FLAG_CRASH_FLUSH,
> -					&ar->dev_flags);
> -
> -			(empty || skip);
> -		}), ATH10K_FLUSH_TIMEOUT_HZ);
> +	ret = wait_event_timeout(ar->htt.empty_tx_wq,
> +				 check_htt_state(ar, skip),
> +				 ATH10K_FLUSH_TIMEOUT_HZ);
>  
>  	if (ret <= 0 || skip)
>  		ath10k_warn(ar, "failed to flush transmit queue (skip %i ar-state %i): %i\n",


Which is why this won't work.  The check_htt_state() function won't
update the "skip" variable, so it is always false here. The test now
fails to detect any of the two "skip conditions".  Not really a big
problem of course, as it only masks a warning.  But still: Your attempt
to clean up has changed the behaviour in an unintentional way.

I'd suggest to leave this alone as it is.  The existing code is really
fine. And testing these odd corner cases is probably difficult, even for
someone with the actual hardware.  I have no idea what will trigger the
ATH10K_FLAG_CRASH_FLUSH flag for example..

It's better to look into some real bug, where you are able to verify a
fix.



Bjørn
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