linux-kernel - Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting

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Date:	Wed, 26 Aug 2015 13:22:49 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Johannes Berg <johannes@...solutions.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>, adrian.hunter@...el.com,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Vince Weaver <vince@...ter.net>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	linux-kernel@...r.kernel.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting

On Wed, 26 Aug 2015 22:05:13 +0200 Peter Zijlstra <peterz@...radead.org> wrote:

> > Is this whole thing overkill?  As far as I can see, the problem which is
> > being addressed only occurs in a couple of places (perf, wifi netlink
> > handling) and could be addressed with some local pr_debug statements.  ie,
> > 
> > #define err_str(e, s) ({
> > 	if (debugging)
> > 		pr_debug("%s:%d: error %d (%s)", __FILE__, __LINE__, e, s);
> > 	e;
> > })
> > 
> > (And I suppose that if this is later deemed inadequate, err_str() could
> > be made more fancy).
> 
> Not really. That is something that's limited to root. Whereas the
> problem is very much wider than that.
> 
> If you set one bit wrong in the pretty large perf_event_attr you've got
> a fair chance of getting -EINVAL on trying to create the event. Good
> luck finding what you did wrong.
> 
> Any user can create events (for their own tasks), this does not require
> root.
> 
> Allowing users to flip your @debugging flag would be an insta DoS.
> 
> Furthermore, its very unfriendly in that you have to (manually) go
> correlate random dmesg output with some program action.

It depends on who the audience is.  If it's developers who are writing
userspace perf tooling then all the above won't be an issue.  If it's
aimed at end users of that tooling then yes.

IOW, we're in the usual situation of discussing implementation before
anyone has explained the requirements.


Also...  we're talking only of perf, so perhaps some perf-specific
reporting scheme would be better, rather than a kernel-wide thing.
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