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

From Peter Zijlstra <peterz@infradead.org>
Newsgroups linux.kernel
Subject Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting
Date 2015-08-26 22:10 +0200
Message-ID <q1Pbb-7Bp-11@gated-at.bofh.it> (permalink)
References (5 earlier) <q1D0l-71b-9@gated-at.bofh.it> <q1D0l-71b-7@gated-at.bofh.it> <q1DjI-7nv-11@gated-at.bofh.it> <q1DjI-7nv-9@gated-at.bofh.it> <q1NVL-5DV-7@gated-at.bofh.it>
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On Wed, Aug 26, 2015 at 11:41:11AM -0700, Andrew Morton wrote:
> On Wed, 26 Aug 2015 09:26:56 +0200 Ingo Molnar <mingo@kernel.org> wrote:
> 
> > 
> > * Ingo Molnar <mingo@kernel.org> wrote:
> > 
> > > ... but back then I didn't feel like complicating an error recovery ABI for the 
> > > needs of the 1%, robust error handling is all about simplicity: if it's not 
> > > simple, tools won't use it.
> > 
> > And note that it needs to be 'simple' in two places for usage to grow naturally: 
> > 
> >   - the usage site in the kernel
> >   - the tooling side that recovers the information.
> > 
> > That's why I think that such a form:
> > 
> > 	return err_str(-EINVAL, "x86/perf: CPU does not support precise sampling");
> > 
> > is obviously simple on the kernel side as it returns -EINVAL, and is very simple 
> > on the tooling side as well, if we are allowed to extend prctl().
> > 
> 
> 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.
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[PATCH v2 0/6] perf: Introduce extended syscall error reporting Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-24 16:40 +0200
  [PATCH v2 5/6] perf/x86/intel/pt: Use extended error reporting in event initialization Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-24 16:40 +0200
  [PATCH v2 6/6] perf/x86/intel/bts: Use extended error reporting in event initialization Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-24 16:40 +0200
  [PATCH v2 1/6] perf: Introduce extended syscall error reporting Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-24 16:40 +0200
    Re: [PATCH v2 1/6] perf: Introduce extended syscall error reporting Andy Shevchenko <andy.shevchenko@gmail.com> - 2015-08-31 20:50 +0200
      Re: [PATCH v2 1/6] perf: Introduce extended syscall error reporting Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-09-01 08:40 +0200
  [PATCH v2 3/6] perf: Annotate some of the error codes with perf_err() Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-24 16:40 +0200
  [PATCH v2 2/6] perf: Add file name and line number to perf extended error reports Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-24 16:40 +0200
  [PATCH v2 4/6] perf/x86: Annotate some of the error codes with perf_err() Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-24 16:40 +0200
  Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-25 10:30 +0200
  Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Johannes Berg <johannes@sipsolutions.net> - 2015-08-25 11:00 +0200
    Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-25 11:10 +0200
      Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-25 11:20 +0200
        Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Johannes Berg <johannes@sipsolutions.net> - 2015-08-25 11:40 +0200
          Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-25 12:10 +0200
            Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Johannes Berg <johannes@sipsolutions.net> - 2015-08-25 12:30 +0200
              Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-26 07:00 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Johannes Berg <johannes@sipsolutions.net> - 2015-08-26 09:10 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-26 09:30 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-26 19:00 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Arnaldo Carvalho de Melo <acme@kernel.org> - 2015-08-26 23:00 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Andrew Morton <akpm@linux-foundation.org> - 2015-08-26 20:50 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Peter Zijlstra <peterz@infradead.org> - 2015-08-26 22:10 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Andrew Morton <akpm@linux-foundation.org> - 2015-08-26 22:30 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error  reporting Vince Weaver <vince@deater.net> - 2015-08-26 23:00 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Andrew Morton <akpm@linux-foundation.org> - 2015-08-26 23:00 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error  reporting Vince Weaver <vince@deater.net> - 2015-08-26 23:20 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-28 12:10 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Arnaldo Carvalho de Melo <acme@infradead.org> - 2015-08-26 23:10 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-26 09:30 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Johannes Berg <johannes@sipsolutions.net> - 2015-08-26 09:40 +0200
                Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Ingo Molnar <mingo@kernel.org> - 2015-08-26 09:10 +0200
        Re: [PATCH v2 0/6] perf: Introduce extended syscall error reporting Alexander Shishkin <alexander.shishkin@linux.intel.com> - 2015-08-26 13:40 +0200

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