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

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Message-ID: <20240911195311.GA16757@redhat.com>
Date: Wed, 11 Sep 2024 21:53:38 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: Roman Kisel <romank@...ux.microsoft.com>
Cc: akpm@...ux-foundation.org, apais@...rosoft.com, benhill@...rosoft.com,
	ebiederm@...ssion.com, linux-kernel@...r.kernel.org,
	ssengar@...rosoft.com, sunilmut@...rosoft.com,
	torvalds@...ux-foundation.org, vdso@...bites.dev,
	workingjubilee@...il.com
Subject: Re: [PATCH 1/1] ptrace: Get tracer PID without reliance on the proc
 FS

Roman,

I can only repeat that we can't understand each other. Quite possibly my bad.

On 09/11, Roman Kisel wrote:
>
> On 09/11, Oleg Nesterov wrote:
>
> > On 09/10, Roman Kisel wrote:
> > >
> > > On 09/09, Oleg wrote:
> > >
> >
> > > > Yet another thing in this discussion I can't understand... sorry, I tried.
> > > > You do not need to teach, say, gdb to recognize this pattern. You can just do
> > > >
> > > > 	$ gdb -ex 'b please_insert_the_breakpoint_here' ...
> > > >
> > > > Nevermind, as I have already said you can safely ignore me. I still do not
> > > > see any "real" use-case for breakpoint_if_debugging(), but I guess that is
> > > > due to my ignorance and lack of imagination.
> > >
> > > I've started this so let me butt in and take up the gaunlet.
> > >
> > > Lambda's would be the most prominent example to me[1]. The toolchain
> > > doesn't give them the user-accesible type and the name as it does for
> > > the functions.
> >
> > And?
>
> You wanted an example of '"real" use-case for breakpoint_if_debugging()':

Then why does your email explain that c++ lambdas don't have a good name?
Why doesi it mention lambdas at all?

> > > > Nevermind, as I have already said you can safely ignore me. I still do not
> > > > see any "real" use-case for breakpoint_if_debugging(), but I guess that is
> > > > due to my ignorance and lack of imagination.
>
> I have provided them, and illustrated how it is tiresome to set the breakpoint
> in the debugger in these cases so can add a call to breakpoint_if_debugging()
> to these places instead.

Instead of what??? Instead of

	#define breakpoint_if_debugging()	\
		asm volatile ("call please_insert_the_breakpoint_here" : ASM_CALL_CONSTRAINT);

plus -ex 'b please_insert_the_breakpoint_here'???

If you say that this is ugly I won't even argue. But instead of what?

Roman, I am leaving this thread, sorry. But let me try to summarize.
Your patch was buggy and you seem to agree. Feel free to send V2 and I will
be happy to review it correctness-wise. But:

	- please keep Eric/Linus cc'ed

	- please try to make your changelog more convincing. And in particular,
	  please explain why !!current->ptrace is not enough and this feature
	  needs the tracer's pid.

	  If possible, please provide a clear/simple/artificial/whatever example
	  of the (pseudo)code which can justify this feature.
Oleg.