Does it always do this, and does it do this immediately upon network use? What is your output (if you can get there) for “lsmod”? Also, what was your method of install…just a complete flash, or some form of “upgrade”? I haven’t personally installed R21.1 yet (hope to soon, working on other things first), so it’s difficult to debug (more information might help).
I’m thinking that one of the known issues in release notes applies. According to R21.1 notes, “2.3 ONBOARD ETHERNET OCASDIONALLY REACHES TIMEOUT HIT NETDEV WATCHDOG TIMEOUT IN R8169 DRIVER”. The release notes go on to mention there is a known linux issue and reaching the NetDev watchdog timer might occur under heavy I/O, and that a workaround is to use a slower ethernet HUB, e.g., 100 Mbps. Implications are that this is purely a linux kernel issue within the R8169 driver.
I’m also thinking there may have been (or maybe not) a mainstream kernel fix for this already, and that if this is true it could be back-ported.
So far as the OOPS goes, I’m wondering if any of this is an intended response from a watchdog…some watchdogs are intended to be configurable to their response, such as forcing a reboot or forcing OOPS. For the moment I have to keep R19.3 on my system so I do not know what is in the /proc/config.gz file. Maybe someone with this file can post it, since some kernel compile options are related to watchdog timers and how they will behave. Disabling a watchdog timer could be a benefit if this is the case (it wouldn’t stop a network stall but would stop the watchdog response).