linux-kernel - RE: [RFC PATCH v2 3/3] ACPI: extlog: Make print_extlog

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Date: Fri, 17 May 2024 14:43:11 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: "Luck, Tony" <tony.luck@...el.com>, "Williams, Dan J"
	<dan.j.williams@...el.com>, Borislav Petkov <bp@...en8.de>
CC: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>, "Rafael J.
 Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
	"rostedt@...dmis.org" <rostedt@...dmis.org>
Subject: RE: [RFC PATCH v2 3/3] ACPI: extlog: Make print_extlog_rcd() log
 unconditionally

Luck, Tony wrote:
> > Given that is has not kept pace the next question is whether the kernel
> > should bother to maintain the contract => "if nothing is watching
> > tracepoints some subset (all?) hardware error messages will be reflected
> > to the kernel log".
> 
> I'm with you for corrected & recoverable errors. The console is a terrible
> place for those logs.
> 
> But it's handy to have fatal errors go to the console. They may make it out to a
> serial port, or be stashed in pstore for later retrieval. Trace event logs that
> are handled by some user level daemon are just going to disappear in a
> puff of reset smoke.

That is true, and arguably that fatal event logging to the kernel log should be
independent of whether userspace is watching. I.e. ras_userpsace_consumers()
gating kernel logging is actively getting in the way when the error severity
implies userspace may not get a chance to see or process the event.

I would need help from Steven on whether ftrace would be amenable to have a
localized tracepoint_printk context to trigger emission of fatal events to the
kernel log in addition to the trace buffer.