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net: provide macros for commonly copied lockless queue stop/wake code

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A lot of drivers follow the same scheme to stop / start queues
without introducing locks between xmit and NAPI tx completions.
I'm guessing they all copy'n'paste each other's code.
The original code dates back all the way to e1000 and Linux 2.6.19.

Smaller drivers shy away from the scheme and introduce a lock
which may cause deadlocks in netpoll.

Provide macros which encapsulate the necessary logic.

The macros do not prevent false wake ups, the extra barrier
required to close that race is not worth it. See discussion in:
https://lore.kernel.org/all/c39312a2-4537-14b4-270c-9fe1fbb91e89@gmail.com/

Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jakub Kicinski
2023-04-06 18:25:33 -07:00
parent 8336462539
commit c91c46de6b
3 changed files with 151 additions and 0 deletions
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include/linux/netdevice.h
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@@ -3335,6 +3335,7 @@ static inline void netif_tx_wake_all_queues(struct net_device *dev)
static __always_inline void netif_tx_stop_queue(struct netdev_queue *dev_queue)
{
/* Must be an atomic op see netif_txq_try_stop() */
set_bit(__QUEUE_STATE_DRV_XOFF, &dev_queue->state);
}