Messages in this thread | | | Subject | Re: new warning caused by ("net-sysfs: update the queue counts in the unregistration path") | From | Antoine Tenart <> | Date | Wed, 28 Sep 2022 11:46:20 +0200 |
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Quoting Kevin Mitchell (2022-09-28 03:27:46) > With the inclusion of d7dac083414e ("net-sysfs: update the queue counts in the > unregistration path"), we have started see the following message during one of > our stress tests that brings an interface up and down while continuously > trying to send out packets on it: > > et3_11_1 selects TX queue 0, but real number of TX queues is 0 > > It seems that this is a result of a race between remove_queue_kobjects() and > netdev_cap_txqueue() for the last packets before setting dev->flags &= ~IFF_UP > in __dev_close_many(). When this message is displayed, netdev_cap_txqueue() > selects queue 0 anyway (the noop queue at this point). As it did before the > above commit, that queue (which I guess is still around due to reference > counting) proceeds to drop the packet and return NET_XMIT_CN. So there doesn't > appear to be a functional change. However, the warning message seems to be > spurious if not slightly confusing.
Do you know the call traces leading to this? Also I'm not 100% sure to follow as remove_queue_kobjects is called in the unregistration path while the test is setting the iface up & down. What driver is used?
As you said and looking around queue 0 is somewhat special and used as a fallback. My suggestion would be to 1) check if the above race is expected 2) if yes, a possible solution would be not to warn when real_num_tx_queues == 0 as in such cases selecting queue 0 would be the expected fallback (and you might want to check places like [1]).
Thanks, Antoine
[1] https://elixir.bootlin.com/linux/latest/source/net/core/dev.c#L4126
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