linux-kernel - Re: [PATCH v2 2/3] compiler: inline does not imply notrace

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Date:   Thu, 25 May 2023 22:28:44 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Nadav Amit <nadav.amit@...il.com>
Cc:     "Arnd Bergmann" <arnd@...db.de>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-ia64@...r.kernel.org, linux-um@...ts.infradead.org,
        Linux-Arch <linux-arch@...r.kernel.org>, linux-mm@...ck.org,
        "Andy Lutomirski" <luto@...nel.org>,
        "Ingo Molnar" <mingo@...hat.com>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        "Borislav Petkov" <bp@...en8.de>, x86@...nel.org,
        Peter Zijlstra <peterz@...radead.org>,
        Nadav Amit <namit@...are.com>
Subject: Re: [PATCH v2 2/3] compiler: inline does not imply notrace

On Thu, 25 May 2023 14:00:39 -0700
Nadav Amit <nadav.amit@...il.com> wrote:

> From: Nadav Amit <namit@...are.com>
> 
> Functions that are marked as "inline" are currently also not tracable.
> This limits tracing functionality for many functions for no reason.
> Apparently, this has been done for two reasons.
> 
> First, as described in commit 5963e317b1e9d2a ("ftrace/x86: Do not
> change stacks in DEBUG when calling lockdep"), it was intended to
> prevent some functions that cannot be traced from being traced as these
> functions were marked as inline (among others).
> 
> Yet, this change has been done a decade ago, and according to Steven
> Rostedt, ftrace should have improved and hopefully resolved nested
> tracing issues by now. Arguably, if functions that should be traced -
> for instance since they are used during tracing - still exist, they
> should be marked as notrace explicitly.
> 
> The second reason, which Steven raised, is that attaching "notrace" to
> "inline" prevented tracing differences between different configs, which
> caused various problem. This consideration is not very strong, and tying
> "inline" and "notrace" does not seem very beneficial. The "inline"
> keyword is just a hint, and many functions are currently not tracable
> due to this reason.
> 
> Disconnect "inline" from "notrace".

FYI, I have a patch queued (still needs to go through testing) that
already does this ;-)

https://lore.kernel.org/all/20230502164102.1a51cdb4@gandalf.local.home/

-- Steve