linux-kernel - Re: [PATCH] [PATCH] cxl: trace: Fix macro safety in CXL_EVT_TP_fast

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Message-ID: <72d355b4-73f8-458d-99e8-8e4f02d5dd79@gmail.com>
Date: Thu, 24 Apr 2025 21:17:28 +0530
From: shaikh kamaluddin <shaikhkamal2012@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: dan.j.williams@...el.com, Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Dave Jiang <dave.jiang@...el.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Ira Weiny <ira.weiny@...el.com>,
 Shiju Jose <shiju.jose@...wei.com>,
 "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>,
 Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>,
 linux-cxl@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [PATCH] cxl: trace: Fix macro safety in
 CXL_EVT_TP_fast_assign

On 4/22/25 00:42, Steven Rostedt wrote:
> On Tue, 22 Apr 2025 00:15:17 +0530
> "shaikh.kamal" <shaikhkamal2012@...il.com> wrote:
>
>> Fix checkpatch.pl detected error
> First, checkpatch.pl should never be used on existing code unless it's
> yours. As the name suggests, it's for checking patches. It's not to check
> what's already been accepted. Please do not submit patches against accepted
> code because of what checkpatch.pl reports.
Thanks for your suggestion.
>
> If you run it on code and it reports something that you find is a real bug,
> then sure, fix it. But don't submit patches on code you do not understand
> just because checkpatch.pl says there's an issue with it.
Okay got it.
>
>> The CXL_EVT_TP_fast_assign macro assigns multiple fields, but does not
>> wrap the body in a `do { ... } while (0)` block. This can lead to
>> unexpected behavior when used in conditional branches.
> Next, this is not a normal macro. It's a trace event macro and
> checkpatch.pl fails miserably on pretty much all tracing macros.
>
> Thanks for your comments.
>
>> Add checks to ensure cxlmd is valid before accessing its fields.
> If it is invalid, and we do what your patch suggests and just not write
> anything, the event it was writing into has already been created. If we
> exit out of this macro, then the event will simply contain garbage, but is
> already on its way to user space. That means the output to user space will
> be garbage. That's a bug. In other words, if cxlmd is NULL, it had better
> not be calling this macro in the fist place!
>
> -- Steve
> Thanks for your suggestions and comments.