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[ Upstream commit 95ecba62e2fd201bcdcca636f5d774f1cd4f1458 ]
Some workloads hit the infamous dev_watchdog() message:
"NETDEV WATCHDOG: eth0 (xxxx): transmit queue XX timed out"
It seems possible to hit this even for perfectly normal
BQL enabled drivers:
1) Assume a TX queue was idle for more than dev->watchdog_timeo
(5 seconds unless changed by the driver)
2) Assume a big packet is sent, exceeding current BQL limit.
3) Driver ndo_start_xmit() puts the packet in TX ring,
and netdev_tx_sent_queue() is called.
4) QUEUE_STATE_STACK_XOFF could be set from netdev_tx_sent_queue()
before txq->trans_start has been written.
5) txq->trans_start is written later, from netdev_start_xmit()
if (rc == NETDEV_TX_OK)
txq_trans_update(txq)
dev_watchdog() running on another cpu could read the old
txq->trans_start, and then see QUEUE_STATE_STACK_XOFF, because 5)
did not happen yet.
To solve the issue, write txq->trans_start right before one XOFF bit
is set :
- _QUEUE_STATE_DRV_XOFF from netif_tx_stop_queue()
- __QUEUE_STATE_STACK_XOFF from netdev_tx_sent_queue()
From dev_watchdog(), we have to read txq->state before txq->trans_start.
Add memory barriers to enforce correct ordering.
In the future, we could avoid writing over txq->trans_start for normal
operations, and rename this field to txq->xoff_start_time.
Fixes: bec251bc8b ("net: no longer stop all TX queues in dev_watchdog()")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://patch.msgid.link/20241015194118.3951657-1-edumazet@google.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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.