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    Subject[PATCH 4.9 146/310] rt2x00: do not pause queue unconditionally on error path
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Stanislaw Gruszka <sgruszka@redhat.com>


    [ Upstream commit 6dd80efd75ce7c2dbd9f117cf585ee2b33a42ee1 ]

    Pausing queue without checking threshold is racy with txdone path.
    Moreover we do not need pause queue on any error, but only if queue
    is full - in case when we send RTS frame ( other cases of almost full
    queue are already handled in rt2x00queue_write_tx_frame() ).

    Patch fixes of theoretically possible problem of pausing empty
    queue.

    Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
    Tested-by: Enrico Mioso <mrkiko.rs@gmail.com>
    Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
    Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
    ---
    drivers/net/wireless/ralink/rt2x00/rt2x00mac.c | 22 ++++++++++++++--------
    1 file changed, 14 insertions(+), 8 deletions(-)

    --- a/drivers/net/wireless/ralink/rt2x00/rt2x00mac.c
    +++ b/drivers/net/wireless/ralink/rt2x00/rt2x00mac.c
    @@ -142,15 +142,25 @@ void rt2x00mac_tx(struct ieee80211_hw *h
    if (!rt2x00dev->ops->hw->set_rts_threshold &&
    (tx_info->control.rates[0].flags & (IEEE80211_TX_RC_USE_RTS_CTS |
    IEEE80211_TX_RC_USE_CTS_PROTECT))) {
    - if (rt2x00queue_available(queue) <= 1)
    - goto exit_fail;
    + if (rt2x00queue_available(queue) <= 1) {
    + /*
    + * Recheck for full queue under lock to avoid race
    + * conditions with rt2x00lib_txdone().
    + */
    + spin_lock(&queue->tx_lock);
    + if (rt2x00queue_threshold(queue))
    + rt2x00queue_pause_queue(queue);
    + spin_unlock(&queue->tx_lock);
    +
    + goto exit_free_skb;
    + }

    if (rt2x00mac_tx_rts_cts(rt2x00dev, queue, skb))
    - goto exit_fail;
    + goto exit_free_skb;
    }

    if (unlikely(rt2x00queue_write_tx_frame(queue, skb, control->sta, false)))
    - goto exit_fail;
    + goto exit_free_skb;

    /*
    * Pausing queue has to be serialized with rt2x00lib_txdone(). Note
    @@ -164,10 +174,6 @@ void rt2x00mac_tx(struct ieee80211_hw *h

    return;

    - exit_fail:
    - spin_lock(&queue->tx_lock);
    - rt2x00queue_pause_queue(queue);
    - spin_unlock(&queue->tx_lock);
    exit_free_skb:
    ieee80211_free_txskb(hw, skb);
    }

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