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    SubjectRe: Attaching a process to cgroups
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    On Mon, 2012-07-23 at 22:41 +0200, Andrea Righi wrote: 
    > On Thu, Jun 21, 2012 at 10:23:02AM +0200, Mike Galbraith wrote:
    > > On Thu, 2012-06-21 at 11:54 +0400, Alexey Vlasov wrote:
    > > > On Wed, Jun 20, 2012 at 02:28:18PM +0200, Mike Galbraith wrote:
    > > > >
    > > > > kernel/cgroup.c::cgroup_attach_task()
    > > > > {
    > > > > ...
    > > > > synchronize_rcu();
    > > > > ...
    > > > > }
    > > >
    > > > So nothing can be done here? (I mean if only I knew how to fix it I
    > > > wouldn't ask about it ;)
    > >
    > > Sure, kill the obnoxious thing, it's sitting right in the middle of the
    > > userspace interface.
    > >
    > > I banged on it a while back (wrt explosive android patches), extracted
    > > RCU from the userspace interface. It seemed to work great, much faster,
    > > couldn't make it explode. I wouldn't bet anything I wasn't willing to
    > > immediately part with that the result was really really safe though ;-)
    > >
    > > -Mike
    >
    > JFYI,
    >
    > I'm testing the following patch in a bunch of hosts and I wasn't able to
    > make any of them to explode, even running a multi-threaded
    > cgroup-intensive workload, but probably I was just lucky (or unlucky,
    > depending on the point of view).
    >
    > It is basically the same Not-signed-off-by work posted by Mike a while
    > ago: https://lkml.org/lkml/2011/4/12/599.
    >
    > In addition, I totally removed the synchronize_rcu() call from
    > cgroup_attach_task() and added the call_rcu -> schedule_work removal
    > also for css_set. The latter looks unnecessary to me from a logical
    > point of view, or maybe I'm missing something, because I can't explain
    > why with it I can't trigger any BUG / oops.
    >
    > Mike, did you make any progress from your old patch?

    No, it worked, but I couldn't prove it was really safe, so let it drop.

    -Mike



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