linux-kernel - Re: [PATCH 1/1] ptrace: Get tracer PID without reliance on the proc FS

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Message-ID: <CAHk-=wiSN1NWzG2W1KCQKoG7mM+RmP+dZ0nWNfEagTwPPiDxXQ@mail.gmail.com>
Date: Fri, 6 Sep 2024 13:26:35 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: Oleg Nesterov <oleg@...hat.com>, "Eric W. Biederman" <ebiederm@...ssion.com>, 
	Andrew Morton <akpm@...ux-foundation.org>, linux-kernel@...r.kernel.org, 
	apais@...rosoft.com, benhill@...rosoft.com, ssengar@...rosoft.com, 
	sunilmut@...rosoft.com, vdso@...bites.dev
Subject: Re: [PATCH 1/1] ptrace: Get tracer PID without reliance on the proc FS

On Fri, 6 Sept 2024 at 13:08, Roman Kisel <romank@...ux.microsoft.com> wrote:
>
> When the process has run into a fatal error and is about to exit, having
> a way to break into the debugger at this exact moment wouldn't change
> anything about the logic of the data processing happening in the process.
> What's so horrible in that to have a way to land in the debugger to see
> what exactly is going on?

I don't buy it.

If you want to debug some fatal behavior, and a debugger *isn't*
attached, you want it to create a core-dump.

And if a debugger *is* attached, it will catch that.

This is basically how abort() has always worked, and it very much is
*not* doing some "let's check if we're being debugged" stuff. Exactly
because that would be a bad idea and an anti-pattern.

The other very traditional model - for example if you do *not* want to
do core-dumps for some reason, and just exit with an error message -
is to just put a breakpoint on the "fatal()" function (or whatever
your "fatal error happened" situation is) using the debugger.

Then the target will behave differently depending on whether it is
being debugged or not BECAUSE THE DEBUGGER ASKED FOR IT, not because
the program decided to act differently when debugged.

In other words, this is a long-solved problem with solid solutions
from before Linux even existed.

              Linus