932ff279a4
Various drivers use xmit_lock internally to synchronise with their transmission routines. They do so without setting xmit_lock_owner. This is fine as long as netpoll is not in use. With netpoll it is possible for deadlocks to occur if xmit_lock_owner isn't set. This is because if a printk occurs while xmit_lock is held and xmit_lock_owner is not set can cause netpoll to attempt to take xmit_lock recursively. While it is possible to resolve this by getting netpoll to use trylock, it is suboptimal because netpoll's sole objective is to maximise the chance of getting the printk out on the wire. So delaying or dropping the message is to be avoided as much as possible. So the only alternative is to always set xmit_lock_owner. The following patch does this by introducing the netif_tx_lock family of functions that take care of setting/unsetting xmit_lock_owner. I renamed xmit_lock to _xmit_lock to indicate that it should not be used directly. I didn't provide irq versions of the netif_tx_lock functions since xmit_lock is meant to be a BH-disabling lock. This is pretty much a straight text substitution except for a small bug fix in winbond. It currently uses netif_stop_queue/spin_unlock_wait to stop transmission. This is unsafe as an IRQ can potentially wake up the queue. So it is safer to use netif_tx_disable. The hamradio bits used spin_lock_irq but it is unnecessary as xmit_lock must never be taken in an IRQ handler. Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au> Signed-off-by: David S. Miller <davem@davemloft.net>
77 lines
2.6 KiB
Text
77 lines
2.6 KiB
Text
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Network Devices, the Kernel, and You!
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Introduction
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============
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The following is a random collection of documentation regarding
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network devices.
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struct net_device allocation rules
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==================================
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Network device structures need to persist even after module is unloaded and
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must be allocated with kmalloc. If device has registered successfully,
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it will be freed on last use by free_netdev. This is required to handle the
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pathologic case cleanly (example: rmmod mydriver </sys/class/net/myeth/mtu )
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There are routines in net_init.c to handle the common cases of
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alloc_etherdev, alloc_netdev. These reserve extra space for driver
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private data which gets freed when the network device is freed. If
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separately allocated data is attached to the network device
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(dev->priv) then it is up to the module exit handler to free that.
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struct net_device synchronization rules
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=======================================
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dev->open:
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Synchronization: rtnl_lock() semaphore.
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Context: process
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dev->stop:
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Synchronization: rtnl_lock() semaphore.
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Context: process
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Note1: netif_running() is guaranteed false
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Note2: dev->poll() is guaranteed to be stopped
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dev->do_ioctl:
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Synchronization: rtnl_lock() semaphore.
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Context: process
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dev->get_stats:
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Synchronization: dev_base_lock rwlock.
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Context: nominally process, but don't sleep inside an rwlock
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dev->hard_start_xmit:
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Synchronization: netif_tx_lock spinlock.
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When the driver sets NETIF_F_LLTX in dev->features this will be
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called without holding netif_tx_lock. In this case the driver
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has to lock by itself when needed. It is recommended to use a try lock
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for this and return -1 when the spin lock fails.
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The locking there should also properly protect against
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set_multicast_list
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Context: BHs disabled
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Notes: netif_queue_stopped() is guaranteed false
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Interrupts must be enabled when calling hard_start_xmit.
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(Interrupts must also be enabled when enabling the BH handler.)
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Return codes:
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o NETDEV_TX_OK everything ok.
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o NETDEV_TX_BUSY Cannot transmit packet, try later
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Usually a bug, means queue start/stop flow control is broken in
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the driver. Note: the driver must NOT put the skb in its DMA ring.
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o NETDEV_TX_LOCKED Locking failed, please retry quickly.
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Only valid when NETIF_F_LLTX is set.
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dev->tx_timeout:
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Synchronization: netif_tx_lock spinlock.
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Context: BHs disabled
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Notes: netif_queue_stopped() is guaranteed true
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dev->set_multicast_list:
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Synchronization: netif_tx_lock spinlock.
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Context: BHs disabled
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dev->poll:
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Synchronization: __LINK_STATE_RX_SCHED bit in dev->state. See
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dev_close code and comments in net/core/dev.c for more info.
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Context: softirq
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