[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-Id: <20150826135616.c96aeed77efbb412d72b8f00@linux-foundation.org>
Date: Wed, 26 Aug 2015 13:56:16 -0700
From: Andrew Morton <akpm@...ux-foundation.org>
To: Vince Weaver <vince@...ter.net>
Cc: Peter Zijlstra <peterz@...radead.org>,
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>,
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 16:50:33 -0400 (EDT) Vince Weaver <vince@...ter.net> wrote:
> On Wed, 26 Aug 2015, Andrew Morton wrote:
>
> > 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.
>
> As a developer of tools that use the perf_event interface directly (PAPI
> and such) I can say this is a common problem (getting unexplained EINVAL
> results) and yes, telling the user to recompile their kernel to enable
> debugging is usually not an option.
Users wouldn't need to recompile.
> I often have to resort to sprinkling the kernel with printks to find the
> source of errors, which is a pain. It's even more fun when the user's
> setup is slightly different enough that I can't reproduce the issue on a
> local machine, which happens often (due to different kernels, distros
> backporting perf fixes, different hardware, different security settings,
> etc).
Suppose you were to tell them "please do `echo 1 > /proc/whatever' then
send me the kernel logs". Would this be good enough?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists