6.1-stable review patch. If anyone has any objections, please let me know.
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From: Jakub Kicinski kuba@kernel.org
[ Upstream commit d2f5c68e3f7157e874a759e382a5eaffa775b869 ]
driver.rst had a historical form of list of common problems. In the age os Sphinx and rendered documentation it's better to use the more usual title + text format.
This will allow us to render kdoc into the output more naturally.
No changes to the actual text.
Signed-off-by: Jakub Kicinski kuba@kernel.org Stable-dep-of: 95ecba62e2fd ("net: fix races in netdev_tx_sent_queue()/dev_watchdog()") Signed-off-by: Sasha Levin sashal@kernel.org --- Documentation/networking/driver.rst | 91 ++++++++++++++++++----------- 1 file changed, 56 insertions(+), 35 deletions(-)
diff --git a/Documentation/networking/driver.rst b/Documentation/networking/driver.rst index 64f7236ff10be..3040a74d421c7 100644 --- a/Documentation/networking/driver.rst +++ b/Documentation/networking/driver.rst @@ -4,15 +4,19 @@ Softnet Driver Issues =====================
-Transmit path guidelines: +Transmit path guidelines +========================
-1) The ndo_start_xmit method must not return NETDEV_TX_BUSY under - any normal circumstances. It is considered a hard error unless - there is no way your device can tell ahead of time when its - transmit function will become busy. +Stop queues in advance +----------------------
- Instead it must maintain the queue properly. For example, - for a driver implementing scatter-gather this means:: +The ndo_start_xmit method must not return NETDEV_TX_BUSY under +any normal circumstances. It is considered a hard error unless +there is no way your device can tell ahead of time when its +transmit function will become busy. + +Instead it must maintain the queue properly. For example, +for a driver implementing scatter-gather this means::
static netdev_tx_t drv_hard_start_xmit(struct sk_buff *skb, struct net_device *dev) @@ -42,56 +46,73 @@ Transmit path guidelines: return NETDEV_TX_OK; }
- And then at the end of your TX reclamation event handling:: +And then at the end of your TX reclamation event handling::
if (netif_queue_stopped(dp->dev) && TX_BUFFS_AVAIL(dp) > (MAX_SKB_FRAGS + 1)) netif_wake_queue(dp->dev);
- For a non-scatter-gather supporting card, the three tests simply become:: +For a non-scatter-gather supporting card, the three tests simply become::
/* This is a hard error log it. */ if (TX_BUFFS_AVAIL(dp) <= 0)
- and:: +and::
if (TX_BUFFS_AVAIL(dp) == 0)
- and:: +and::
if (netif_queue_stopped(dp->dev) && TX_BUFFS_AVAIL(dp) > 0) netif_wake_queue(dp->dev);
-2) An ndo_start_xmit method must not modify the shared parts of a - cloned SKB. +No exclusive ownership +---------------------- + +An ndo_start_xmit method must not modify the shared parts of a +cloned SKB. + +Timely completions +------------------ + +Do not forget that once you return NETDEV_TX_OK from your +ndo_start_xmit method, it is your driver's responsibility to free +up the SKB and in some finite amount of time.
-3) Do not forget that once you return NETDEV_TX_OK from your - ndo_start_xmit method, it is your driver's responsibility to free - up the SKB and in some finite amount of time. +For example, this means that it is not allowed for your TX +mitigation scheme to let TX packets "hang out" in the TX +ring unreclaimed forever if no new TX packets are sent. +This error can deadlock sockets waiting for send buffer room +to be freed up.
- For example, this means that it is not allowed for your TX - mitigation scheme to let TX packets "hang out" in the TX - ring unreclaimed forever if no new TX packets are sent. - This error can deadlock sockets waiting for send buffer room - to be freed up. +If you return NETDEV_TX_BUSY from the ndo_start_xmit method, you +must not keep any reference to that SKB and you must not attempt +to free it up.
- If you return NETDEV_TX_BUSY from the ndo_start_xmit method, you - must not keep any reference to that SKB and you must not attempt - to free it up. +Probing guidelines +==================
-Probing guidelines: +Address validation +------------------ + +Any hardware layer address you obtain for your device should +be verified. For example, for ethernet check it with +linux/etherdevice.h:is_valid_ether_addr() + +Close/stop guidelines +=====================
-1) Any hardware layer address you obtain for your device should - be verified. For example, for ethernet check it with - linux/etherdevice.h:is_valid_ether_addr() +Quiescence +----------
-Close/stop guidelines: +After the ndo_stop routine has been called, the hardware must +not receive or transmit any data. All in flight packets must +be aborted. If necessary, poll or wait for completion of +any reset commands.
-1) After the ndo_stop routine has been called, the hardware must - not receive or transmit any data. All in flight packets must - be aborted. If necessary, poll or wait for completion of - any reset commands. +Auto-close +----------
-2) The ndo_stop routine will be called by unregister_netdevice - if device is still UP. +The ndo_stop routine will be called by unregister_netdevice +if device is still UP.