#22387: bgmac (Broadcom 47xx) "oversized packet" kernel panic
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Reporter: cds@… | Owner: developers
Type: defect | Status: new
Priority: normal | Milestone:
Component: kernel | Version: Chaos Calmer 15.05
Keywords: |
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Hi! I've recently flashed Chaos Calmer onto a Netgear N300 (WNR3500L v1)
using the official OpenWRT image from
https://downloads.openwrt.org/chaos_calmer/15.05.1/brcm47xx/mips74k/openwrt-15.05.1
-brcm47xx-mips74k-netgear-wnr3500l-v1-north-america-squashfs.chk and I
have found a bit of a problem.
Under specific high-bandwidth loads, I get a kernel panic. The relevant
part of the panic, IMO:
{{{
<3>[ 2069.830000] bgmac bcma0:2: Found oversized packet at slot 108, DMA
issue!
<0>[ 2069.890000] skbuff: skb_over_panic: text:801b8c08 len:1741 put:1741
head:82b24740 data:82b24740 tail:0x82b24e0d end:0x82b24da0 de
v:<NULL>
}}}
Examining the relevant kernel code, I found this: http://lxr.free-
electrons.com/source/drivers/net/ethernet/broadcom/bgmac.c#L458
It appears that the maths that determines whether a packet is oversized is
a little suspect, but I can't see the bug immediately. On two different
trials, I've noticed that the len: and put: in the panic are the same both
times.
To reproduce, we have been using youtube-dl to stream ~8MiB/s of video
through the router's WAN port. This reliably crashes the router after a
few seconds of load.
I was not sure whether adjusting the MTU on the WAN port would mitigate
this bug. It doesn't help; I lowered the MTU from 1500 to 1442, but it did
not improve behavior.
I'm marking this as kernel component because the bug is very obviously
somewhere in the kernel.
Thanks!
~ C.
--
Ticket URL: <https://dev.openwrt.org/ticket/22387>
OpenWrt <http://openwrt.org>
Opensource Wireless Router Technology
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