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iwlagn: fix a race in the unmapping of the TFDs 

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>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
This commit is contained in:
Emmanuel Grumbach 2011-10-10 07:27:02 -07:00 committed by John W. Linville
parent b319d3eb96
commit 984ecb9293
1 changed files with 3 additions and 0 deletions
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3
drivers/net/wireless/iwlwifi/iwl-trans-pcie.c
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@ -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);
while (q->write_ptr != q->read_ptr) {
/* The read_ptr needs to bound by q->n_window */
iwlagn_txq_free_tfd(trans, txq, get_cmd_index(q, q->read_ptr),
dma_dir);
q->read_ptr = iwl_queue_inc_wrap(q->read_ptr, q->n_bd);
}
spin_unlock_irqrestore(&trans->shrd->sta_lock, flags);
}
/**