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c542b39b60
The TX ring maintained by the tg3 driver can end up in the state, when it
has packets queued for sending but the NIC hardware is not informed, so no
progress is made. This leads to a multi-second interruption in network
traffic followed by dev_watchdog() firing and resetting the queue.
The specific sequence of steps is:
1. tg3_start_xmit() is called at least once and queues packet(s) without
updating tnapi->prodmbox (netdev_xmit_more() returns true)
2. tg3_start_xmit() is called with an SKB which causes tg3_tso_bug() to be
called.
3. tg3_tso_bug() determines that the SKB is too large, ...
if (unlikely(tg3_tx_avail(tnapi) <= frag_cnt_est)) {
... stops the queue, and returns NETDEV_TX_BUSY:
netif_tx_stop_queue(txq);
...
if (tg3_tx_avail(tnapi) <= frag_cnt_est)
return NETDEV_TX_BUSY;
4. Since all tg3_tso_bug() call sites directly return, the code updating
tnapi->prodmbox is skipped.
5. The queue is stuck now. tg3_start_xmit() is not called while the queue
is stopped. The NIC is not processing new packets because
tnapi->prodmbox wasn't updated. tg3_tx() is not called by
tg3_poll_work() because the all TX descriptions that could be freed has
been freed:
/* run TX completion thread */
if (tnapi->hw_status->idx[0].tx_consumer != tnapi->tx_cons) {
tg3_tx(tnapi);
6. Eventually, dev_watchdog() fires triggering a reset of the queue.
This fix makes sure that the tnapi->prodmbox update happens regardless of
the reason tg3_start_xmit() returned.
Signed-off-by: Alex Pakhunov <alexey.pakhunov@spacex.com>
Signed-off-by: Vincent Wong <vincent.wong2@spacex.com>
Reviewed-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.