Messages in this thread |  | | Date | Thu, 26 Jan 2012 19:32:23 +0100 | | From | Ingo Molnar <> | | Subject | Re: Fixing perf top --user shortcoming was: Re: [GIT PULL 0/9] perf/core improvements and fixes |
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* Arnaldo Carvalho de Melo <acme@infradead.org> wrote:
> > > 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? > > IIRC one of them was a child of sshd, that runs as root and > then changes the child ownership to the user logging in.
It's probably privileged then - or at least not sufficiently deprivileged.
Skipping them ought to be the right solution - it's not like such tasks tend to create a lot of overhead worth profiling. They are also not debuggable via gdb so they are not part of the user's development session and such.
> I'll continue investigation but probably for now the first > thing to do is to just remove them from the thread_map when > they return -EPERM.
Yeah. Maybe warn about them in verbose mode or such.
> > 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? > > Yeah, that can be done, while debugging I'll emit a warning > with the resulting thread_map of "special tasks" to figure out > what makes them special.
Ok, sounds great!
Thanks,
Ingo
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