linux-kernel - RE: [PATCH v2] RAS: Fix the trace_show() function to output trace

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Date:   Mon, 17 Oct 2022 16:09:23 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] RAS: Fix the trace_show() function to output
 trace_count

> Still misleading:
>
> $ cat /sys/kernel/debug/ras/daemon_active
> 1

Agreed. It needs user to interpret the answer. The filename would lead
them to think "1" means the daemon is active, but its actually just a count
of how many times the file is concurrently open (which includes the
"cat" process reading the file).

> I don't know, maybe we should teach RAS daemons to ->write() into that
> file their name and PID so that the trace_count counts *only* the RAS
> daemons not any reader...

Should have thought of this earlier ... changing user space semantics
is hard. Even with only one user, there is a long transition period where
new kernels are running with old rasdaemon and vice versa.

How about:

	seq_printf(m, "%d\n", atomic_read(&trace_count) - 1);

with a comment that users reading the file only want to know if anyone
else has it open?

-Tony