Messages in this thread | | | Subject | Re: Attaching a process to cgroups | From | Mike Galbraith <> | Date | Wed, 27 Jun 2012 09:23:31 +0200 |
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On Tue, 2012-06-26 at 11:06 -0700, Paul E. McKenney 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 ;-) > > Or replace it with synchronize_rcu_expedited(). You can "get lucky" > for quite some time removing synchronize_rcu() calls!
s/remove/replace, but yup. A company that wanted to use the android patches plus my tinkering showed a fix they needed on top to close a race discovered in their testing. So yeah, even when all seems fine, extracting synchronize_rcu() may expose evils you couldn't encounter before, and didn't happen to encounter afterward.
-Mike
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