Re: [PATCH 17/34] iwlagn: fix a race in the unmapping of the TFDs

[Stanislaw Gruszka <sgruszka@redhat.com>]

On Mon, Oct 10, 2011 at 07:27:02AM -0700, Wey-Yi Guy wrote:
> While inspecting the code, I saw that iwl_tx_queue_unmap modifies
> the read pointer of the Tx queue without taking any locks. This means
> that it can race with the reclaim flow. This can possibly lead to
> a DMA warning complaining that we unmap the same buffer twice.
> 
> This is more a W/A than a fix since it is really weird to take
> sta_lock inside iwl_tx_queue_unmap, but it can help until we revamp
> the locking model in the transport layer.
> 
> Signed-off-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
> Signed-off-by: Wey-Yi Guy <wey-yi.w.guy@intel.com>
> ---
>  drivers/net/wireless/iwlwifi/iwl-trans-pcie.c |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/net/wireless/iwlwifi/iwl-trans-pcie.c b/drivers/net/wireless/iwlwifi/iwl-trans-pcie.c
> index 60067c7..f69aecb 100644
> --- a/drivers/net/wireless/iwlwifi/iwl-trans-pcie.c
> +++ b/drivers/net/wireless/iwlwifi/iwl-trans-pcie.c
> @@ -406,6 +406,7 @@ static void iwl_tx_queue_unmap(struct iwl_trans *trans, int txq_id)
>  	struct iwl_tx_queue *txq = &trans_pcie->txq[txq_id];
>  	struct iwl_queue *q = &txq->q;
>  	enum dma_data_direction dma_dir;
> +	unsigned long flags;
>  
>  	if (!q->n_bd)
>  		return;
> @@ -418,12 +419,14 @@ static void iwl_tx_queue_unmap(struct iwl_trans *trans, int txq_id)
>  	else
>  		dma_dir = DMA_TO_DEVICE;
>  
> +	spin_lock_irqsave(&trans->shrd->sta_lock, flags);
sta_lock does not look like right lock to use.

Stanislaw