On 09/26/2015 10:36 PM, David Miller wrote:
From: Alexander Duyck <adu...@mirantis.com>
Date: Tue, 22 Sep 2015 14:56:08 -0700
Rather than carry around a value of budget that is 0 or less we can instead
just loop through and pass 0 to each napi->poll call. If any driver
returns a value for work done that is non-zero then we can report that
driver and continue rather than allowing a bad actor to make the budget
value negative and pass that negative value to napi->poll.
Unfortunately we have drivers that won't do any TX work if the budget
is zero.
Well that is what we are doing right now. The fact is the call starts
out with a budget of 0, and it is somewhat hidden from the call since
the budget is assigned a value of 0 in netpoll_poll_dev. That is one of
the things I was wanting do address because that is clear as mud from
looking at poll_one_napi. Based on the code you would assume budget
starts out as a non-zero value and it doesn't.
Using the budget for TX work is unfortunate and not the recommended
way for drivers to do things, but it's not explicitly disallowed
either.
So I'm not applying this because it definitely has the potential
to break something.
Sorry.
I don't see how this introduces a regression when all I am doing is
avoiding tracking a value that should be 0 assuming everything is
working correctly. If work returns a non-zero value with the code as it
currently is then the WARN_ONCE is triggered, and the value of budget is
becoming negative. I would consider a negative budget value worse than
a 0 budget value.
I'll go back through the patch and rebase it since it looks like Neil
had to submit a v3 of his patch and it may have impacted mine. However
perhaps we need to revisit this code if you think it is risky as the
only thing my changes did is remove the ability for the budget value to
go from 0 to negative and then passing that negative value into the
function.
- Alex
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