Re: [BUG] perf record: --uid=x fails

[Stephane Eranian]

On Tue, Jan 15, 2013 at 3:58 PM, Arnaldo Carvalho de Melo
<acme@xxxxxxxxxx> wrote:
>
> Em Mon, Jan 14, 2013 at 03:14:02PM +0100, Stephane Eranian escreveu:
> > Hi,
> >
> > I was trying to use the --uid option of perf record but it fails for
> > me no matter
> > what I tried. Looks like the goal of this option is to measure ALL the processes
> > owned by the specified uid. Each process is measured in per-thread mode.
> >
> > However for me it failed on all my attempts when running with 3.8.0-rc3 on
> > Ubuntu Quantal.
> >
> > $ perf record --uid=eranian sleep 4
> > Error:
> > Permission error - are you root?
> > Consider tweaking /proc/sys/kernel/perf_event_paranoid:
> >  -1 - Not paranoid at all
> >   0 - Disallow raw tracepoint access for unpriv
> >   1 - Disallow cpu events for unpriv
> >   2 - Disallow kernel profiling for unpriv
> > sleep: Terminated
> >
> > You don't want to be root to run this command.  Should not require
>
> But you have to due to the problem you noticed below.
>
> > to measure the processes I own. So the error message is confusing
> > here.
>
> indeed
>
> > After some debugging, I came to the conclusion that this command
> > fails when it hits the sshd daemon:
> >
> > eranian   2439  0.0  0.0 110424  1968 ?        S    15:07   0:00 sshd:
> > eranian@pts/2
> > root      2301  0.0  0.0 110424  4420 ?        Ss   15:07   0:00 sshd:
> > eranian [priv]
> >
> > I mean the sshd process owned by me. It is owned by me but I cannot attached
> > an event to it. I get EACCES and I suspect it's because of missing
> > ptrace privilege.
> > The sshd binary is obviously not setuid. So there is something else preventing
> > ptrace. In fact, even strace -p 2349 fails. Looked online and there
> > were a couple
> > of mentions to the Yama security model and the ptrace_scope sysctl
> > control. I tried
> > that and it did not help.
> >
> > So looks to me that something is broken somewhere. If the kernel
> > restrictions are
> > normal, then I think perf record should warn that it has to skip the
> > sshd process and
> > continue with the other processes owned by me. That  seems more useful than the
> > current situation. But I may be missing something here. If so please
> > explain to me.
>
> Right, I need to resume working on properly fixing this, I got
> sidetracked when I got the same point as you in the above analysis :-\
>
> Will try to recover the conversations I had about this.
>
What I don't understand is how it could have ever worked?
Or maybe I ran into this just because I use ssh to connect to my machine.

>
> - Arnaldo
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