linux-kernel - Re: [RFC] better visibility into kworkers

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Message-ID: <20180517074202.GA3091@avx2>
Date:   Thu, 17 May 2018 10:42:02 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     lennart@...ttering.net
Cc:     tj@...nel.org, torvalds@...ux-foundation.org, carlos@...ha.com,
        luto@...capital.net, akpm@...ux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] better visibility into kworkers

> The kernel APIs for all this aren't really good
> though, and I always was reluctant to check for PF_KTHREAD, as that
> flag is neither documented for userspace, nor available in any
> userspace-accessible headers. However, I wanted to tighten this a bit,
> and hence we now define the flag in our own code, as it appeared to me
> otherwise there was no chance to ever make this fully robust.

PF_KTHREAD was introduced in 2.6.27 and its value appears to be stable
since then. I think it should be retroactively declared part of ABI
otherwise people will continue to rediscover that all other means do not
work.

Empty /proc/*/exe is second best option for systemd and it's only one
system call.