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

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Date:   Tue, 18 Oct 2022 07:36:53 -0700
From:   Tony Luck <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

On Mon, Oct 17, 2022 at 09:40:09PM +0200, Borislav Petkov wrote:
> Question is, what is your goal with this?

I ran into it while fixing:

  https://lore.kernel.org/all/20221006163258.318916-1-tony.luck@intel.com/

when I just used "cat daemon_active" to check status and was confused
by the lack of any output. Looked at the code and saw the silly

	return atomic_read(&trace_count);

which does nothing useful.

Maybe if there isn't a reasonable thing to output, that could be
changed to:

static int trace_show(struct seq_file *m, void *v)
{
	/*
	 * User should use "lsof daemon_active" if they want to 
	 * know if there is a process consuming trace error records
	 */
	return 0;
}

Sadly, we need to have a trace_show() function. If trace_open() just
does:

	return single_open(file, NULL, NULL);

then we get a deref NULL OOPs if somebody does "cat daemon_active" :-(

-Tony