linux-kernel - Re: Weird issue with epoll and kernel >= 5.0

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Message-ID: <72cde0de-6f4a-4928-d01b-1783ac3ee6e4@moonlit-rail.com>
Date:   Sat, 28 Mar 2020 15:18:12 -0400
From:   Kris Karas <linux-1993@...nlit-rail.com>
To:     Linux Kernel <linux-kernel@...r.kernel.org>
Cc:     omar.kilani@...il.com
Subject: Re: Weird issue with epoll and kernel >= 5.0

Hi Omar -

Omar Kilani wrote:
> I've observed an issue with epoll and kernels 5.0 and above when a
> system is generating a lot of epoll events.

It's tough getting an audience here on LK, unless you happen to 
cross-post to one of the very specific mailing lists (or directly to 
individuals) who maintain a particular subsystem.  I just rejoined LK 
after a 15 year hiatus; it's a rather different neighborhood. *cough*  
But I digress.

My first question on your issue is, after booting, how long does it take 
to show up?  Can you reproduce it fairly easily?  If the answer is 
"Yes," and you seem to be able to afford the resources for a multi-CPU 
VM, then making a bisecting run would likely narrow it down to something 
you could then email directly to the relevant maintainer.

If you are not already familiar with bisecting, the git documentation on 
bisecting is the definitive reference:
https://git-scm.com/docs/git-bisect
But it is quite long.  You can usually find a more abbreviated version 
by googling for "<yourdistroname> git bisect"; the ones for Arch and 
Ubuntu are pretty decent.

Once you know which file is relevant, you can run:

$ ./scripts/get_maintainer.pl --file drivers/foo/bar.c

... or whatever "git bisect" says is the culprit file, and use the 
script output as the To: for your email message.

Good luck!
Kris