From: Jacob Keller jacob.e.keller@intel.com
[ Upstream commit 4ccdc013b0ae04755a8f7905e0525955d52a77d0 ]
Hardware related to the igb driver has a limitation of only handling one Tx timestamp at a time. Thus, the driver uses a state bit lock to enforce that only one timestamp request is honored at a time.
Unfortunately this suffers from a simple race condition. The bit lock is not cleared until after skb_tstamp_tx() is called notifying the stack of a new Tx timestamp. Even a well behaved application which sends only one timestamp request at once and waits for a response might wake up and send a new packet before the bit lock is cleared. This results in needlessly dropping some Tx timestamp requests.
We can fix this by unlocking the state bit as soon as we read the Timestamp register, as this is the first point at which it is safe to unlock.
To avoid issues with the skb pointer, we'll use a copy of the pointer and set the global variable in the driver structure to NULL first. This ensures that the next timestamp request does not modify our local copy of the skb pointer.
This ensures that well behaved applications do not accidentally race with the unlock bit. Obviously an application which sends multiple Tx timestamp requests at once will still only timestamp one packet at a time. Unfortunately there is nothing we can do about this.
Reported-by: David Mirabito davidm@metamako.com Signed-off-by: Jacob Keller jacob.e.keller@intel.com Tested-by: Aaron Brown aaron.f.brown@intel.com Signed-off-by: Jeff Kirsher jeffrey.t.kirsher@intel.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- drivers/net/ethernet/intel/igb/igb_ptp.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/drivers/net/ethernet/intel/igb/igb_ptp.c b/drivers/net/ethernet/intel/igb/igb_ptp.c index a7895c4cbcc3..9eb9b68f8935 100644 --- a/drivers/net/ethernet/intel/igb/igb_ptp.c +++ b/drivers/net/ethernet/intel/igb/igb_ptp.c @@ -721,6 +721,7 @@ void igb_ptp_rx_hang(struct igb_adapter *adapter) **/ static void igb_ptp_tx_hwtstamp(struct igb_adapter *adapter) { + struct sk_buff *skb = adapter->ptp_tx_skb; struct e1000_hw *hw = &adapter->hw; struct skb_shared_hwtstamps shhwtstamps; u64 regval; @@ -748,10 +749,17 @@ static void igb_ptp_tx_hwtstamp(struct igb_adapter *adapter) shhwtstamps.hwtstamp = ktime_add_ns(shhwtstamps.hwtstamp, adjust);
- skb_tstamp_tx(adapter->ptp_tx_skb, &shhwtstamps); - dev_kfree_skb_any(adapter->ptp_tx_skb); + /* Clear the lock early before calling skb_tstamp_tx so that + * applications are not woken up before the lock bit is clear. We use + * a copy of the skb pointer to ensure other threads can't change it + * while we're notifying the stack. + */ adapter->ptp_tx_skb = NULL; clear_bit_unlock(__IGB_PTP_TX_IN_PROGRESS, &adapter->state); + + /* Notify the stack and free the skb after we've unlocked */ + skb_tstamp_tx(skb, &shhwtstamps); + dev_kfree_skb_any(skb); }
/**