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https://github.com/torvalds/linux
05 April 2024, 19:05:47 UTC
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Tip revision: 637f847b68741de42547d5f846c71ed5fe859b6e authored by TarAldarion on 02 March 2020, 12:13:05 UTC
Fix for packets being rejected in the ring buffer used by the xHCI controller. When a packet larger than MTU arrives in Linux from the modem, it is discarded with -EOVERFLOW error (Babble error). This is seen on USB3.0 and USB2.0 busses. This is essentially because the MRU (Max Receive Size) is not a separate entity to the MTU (Max Transmit Size) and the received packets can be larger than those transmitted. Following the babble error there were an endless supply of zero-length URBs which are rejected with -EPROTO (increasing the rx input error counter each time). This is only seen on USB3.0. These continue to come ad infinitum until the modem is shutdown. There appears to be a bug in the core USB handling code in Linux that doesn't deal well with network MTUs smaller than 1500 bytes. By default the dev->hard_mtu (the real MTU) is in lockstep with dev->rx_urb_size (essentially an MRU), and it's the latter that is causing trouble. This has nothing to do with the modems; the issue can be reproduced by getting a USB-Ethernet dongle, setting the MTU to 1430, and pinging with size greater than 1406.
Tip revision: 637f847
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.clang-format -rw-r--r-- 15.0 KB
.cocciconfig -rw-r--r-- 59 bytes
.get_maintainer.ignore -rw-r--r-- 71 bytes
.gitattributes -rw-r--r-- 62 bytes
.gitignore -rw-r--r-- 1.8 KB
.mailmap -rw-r--r-- 14.8 KB
COPYING -rw-r--r-- 496 bytes
CREDITS -rw-r--r-- 97.4 KB
Kbuild -rw-r--r-- 1.3 KB
Kconfig -rw-r--r-- 595 bytes
MAINTAINERS -rw-r--r-- 532.8 KB
Makefile -rw-r--r-- 59.0 KB
README -rw-r--r-- 727 bytes

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