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Message-ID: <20120126130919.GA20115@elte.hu>
Date: Thu, 26 Jan 2012 14:09:19 +0100
From: Ingo Molnar <mingo@...e.hu>
To: Arnaldo Carvalho de Melo <acme@...radead.org>
Cc: linux-kernel@...r.kernel.org, David Ahern <dsahern@...il.com>,
David Daney <david.daney@...ium.com>,
Frederic Weisbecker <fweisbec@...il.com>,
Jan Beulich <jbeulich@...e.com>,
Joerg Roedel <joerg.roedel@....com>,
Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
Mike Galbraith <efault@....de>,
Namhyung Kim <namhyung.kim@....com>,
Paul Mackerras <paulus@...ba.org>,
Peter Zijlstra <peterz@...radead.org>,
Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
Stephane Eranian <eranian@...gle.com>
Subject: Re: Fixing perf top --user shortcoming was: Re: [GIT PULL 0/9]
perf/core improvements and fixes
* Arnaldo Carvalho de Melo <acme@...radead.org> wrote:
> > So what does --uid do which perf record --pid 1234 wouldnt
> > already do? By all means --uid ought to be a fancy way of
> > doing a whole bunch of perf record --pid 1234 profiling
> > sessions, at once.
>
> I stopped at the kernel, i.e. used what can be done with what
> is available from the kernel right now, the diagnosis was sent
> in private, but boils down to:
>
> +++ b/kernel/events/core.c
> @@ -2636,7 +2636,8 @@ find_lively_task_by_vpid(pid_t vpid)
>
> /* Reuse ptrace permission checks for now. */
> err = -EACCES;
> - if (!ptrace_may_access(task, PTRACE_MODE_READ))
> + if (perf_paranoid_tracepoint_raw() &&
> + !ptrace_may_access(task, PTRACE_MODE_READ))
> goto errout;
>
> return task;
>
> ptrace_may_access(task, PTRACE_MODE_READ) fails for some tasks
> owned by the user because, IIRC, in __ptrace_may_access:
Which tasks are these, are they privileged in any sense?
If yes and if most of the 'real' tasks a user have can be
profiled just fine then i think we should just skip the
privileged tasks and not abort the profiling session?
Thanks,
Ingo
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