62f94c2101
It was discovered that simple program which indefinitely sends 200b UDP
packets and runs on TI AM574x SoC (SMP) under RT Kernel triggers network
watchdog timeout in TI CPSW driver (<6 hours run). The network watchdog
timeout is triggered due to race between cpsw_ndo_start_xmit() and
cpsw_tx_handler() [NAPI]
cpsw_ndo_start_xmit()
if (unlikely(!cpdma_check_free_tx_desc(txch))) {
txq = netdev_get_tx_queue(ndev, q_idx);
netif_tx_stop_queue(txq);
^^ as per [1] barier has to be used after set_bit() otherwise new value
might not be visible to other cpus
}
cpsw_tx_handler()
if (unlikely(netif_tx_queue_stopped(txq)))
netif_tx_wake_queue(txq);
and when it happens ndev TX queue became disabled forever while driver's HW
TX queue is empty.
Fix this, by adding smp_mb__after_atomic() after netif_tx_stop_queue()
calls and double check for free TX descriptors after stopping ndev TX queue
- if there are free TX descriptors wake up ndev TX queue.
[1] https://www.kernel.org/doc/html/latest/core-api/atomic_ops.html
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Reviewed-by: Ivan Khoronzhuk <ivan.khoronzhuk@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
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README
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. 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.