On Tue, Aug 03, 2010 at 08:44:01PM -0700, Paul Menage wrote: > On Fri, Jul 30, 2010 at 4:57 PM, Ben Blum <bblum@xxxxxxxxxxxxxx> wrote: > > + * The threadgroup_fork_lock prevents threads from forking with > > + * CLONE_THREAD while held for writing. Use this for fork-sensitive > > + * threadgroup-wide operations. It's taken for reading in fork.c in > > + * copy_process(). > > + * Currently only needed write-side by cgroups. > > + */ > > + struct rw_semaphore threadgroup_fork_lock; > > +#endif > > I'm not sure how best to word this comment, but I'd prefer something like: > > "The threadgroup_fork_lock is taken in read mode during a CLONE_THREAD > fork operation; taking it in write mode prevents the owning > threadgroup from adding any new threads and thus allows you to > synchronize against the addition of unseen threads when performing > threadgroup-wide operations. New-process forks (without CLONE_THREAD) > are not affected." That sounds good. > As far as the #ifdef mess goes, it's true that some people don't have > CONFIG_CGROUPS defined. I'd imagine that these are likely to be > embedded systems with a fairly small number of processes and threads > per process. Are there really any such platforms where the cost of a > single extra rwsem per process is going to make a difference either in > terms of memory or lock contention? I think you should consider making > these additions unconditional. That's certainly an option, but I think it would be clean enough to put static inline functions just under the signal_struct definition. Thoughts? > > Paul > -- Ben _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
