linux-kernel - Re: [PATCH v6 5/6] tracing: Show inode and device major:minor in deferred user space stacktrace

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Message-ID: <20250828164819.51e300ec@batman.local.home>
Date: Thu, 28 Aug 2025 16:48:19 -0400
From: Steven Rostedt <rostedt@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>,
 linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 bpf@...r.kernel.org, x86@...nel.org, Masami Hiramatsu
 <mhiramat@...nel.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 Josh Poimboeuf <jpoimboe@...nel.org>, Peter Zijlstra
 <peterz@...radead.org>, Ingo Molnar <mingo@...nel.org>, Jiri Olsa
 <jolsa@...nel.org>, Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung
 Kim <namhyung@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Andrii
 Nakryiko <andrii@...nel.org>, Indu Bhagat <indu.bhagat@...cle.com>, "Jose
 E. Marchesi" <jemarch@....org>, Beau Belgrave <beaub@...ux.microsoft.com>,
 Jens Remus <jremus@...ux.ibm.com>, Andrew Morton
 <akpm@...ux-foundation.org>, Florian Weimer <fweimer@...hat.com>, Sam James
 <sam@...too.org>, Kees Cook <kees@...nel.org>, "Carlos O'Donell"
 <codonell@...hat.com>
Subject: Re: [PATCH v6 5/6] tracing: Show inode and device major:minor in
 deferred user space stacktrace

On Thu, 28 Aug 2025 13:38:33 -0700
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Thu, 28 Aug 2025 at 13:17, Steven Rostedt <rostedt@...nel.org> wrote:
> >  
> > >
> > > That should be simple and straightforward, and hashing two pointers
> > > should be simple and straightforward.  
> >
> > Would a hash of these pointers have any collisions? That would be bad.  
> 
> What? Collisions in 64 bits when you have a handful of cases around?
> Not an issue unless you picked your hash to be something ridiculous.
> 

Since I only need a unique identifier, and it appears that the
vma->vm_file->f_inode pointer is unique, would just using that be OK?

I could run it through the same hash algorithm that "%p" goes through so
that it's not a real memory address.

As getting to the path does require some more logic to get to. Not to
mention, this may later need to handle JIT code (and we'll need a way
to map to that too).

-- Steve