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Message-ID: <20120126122200.GA9128@infradead.org>
Date: Thu, 26 Jan 2012 10:22:00 -0200
From: Arnaldo Carvalho de Melo <acme@...radead.org>
To: Ingo Molnar <mingo@...e.hu>
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: Fixing perf top --user shortcoming was: Re: [GIT PULL 0/9] perf/core
improvements and fixes
Em Thu, Jan 26, 2012 at 12:16:48PM +0100, Ingo Molnar escreveu:
> * Arnaldo Carvalho de Melo <acme@...radead.org> wrote:
> > The --uid feature works for root, we still need to
> > sort out that paranoia with some threads owned by a user that
> > prevents 'perf --uid non-root-user' to work for
> > 'non-root-user'.
> Just wondering what detail causes that failure - the whole point
> of --uid mingo would be to enable nonprivileged users to do
> 'session wide' profiling, *especially* if paranoia is high.
> 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:
const struct cred *cred = current_cred(), *tcred;
/* May we inspect the given task?
* This check is used both for attaching with ptrace
* and for allowing access to sensitive information in /proc.
*
* ptrace_attach denies several cases that /proc allows
* because setting up the necessary parent/child relationship
* or halting the specified task is impossible.
*/
int dumpable = 0;
<SNIP>
if (!dumpable && !task_ns_capable(task, CAP_SYS_PTRACE))
return -EPERM;
fails.
The patch above is not any kind of solution, just a way to make it work
when paranoia is set to -1 (thus perf_paranoid_tracepoint_raw in the
POC) and show where the problem lies, ideas? Peter?
> [ Btw, we should probably alias --user to --uid as well, as that
> might be the intuitive thing people would typically use? ]
I'll do that
> Anyway, pulled, thanks a lot Arnaldo!
>
> One detail: don't we want some of these fixes cherry-picked into
> perf/urgent as well?
Yeah, I'll prepare a perf-urgent-for-ingo signed tag.
> Thanks,
>
> Ingo
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