On Thu, Aug 6, 2009 at 2:58 AM, Louis Rilling<Louis.Rilling@xxxxxxxxxxx> wrote: > > mutex_lock_nested is not enough, since this would require putting each thread's > mutex in a different class. Again, something like mutex_lock_nest_lock() is > the solution, especially since Peter's recent improvement. > OK, well if lockdep can't currently handle the "writer takes a lock on every thread" model, then maybe we should go with a simpler model until someone shows a performance issue with it? Ben's original patches had a per-task_struct lock, and a thread forking with CLONE_VM would down_read() its group leader's lock. Something that's even simpler (doesn't have to deal with thread group leader changing due to an execve()), and avoids the per-task_struct overhead would be to put the lock in sighand_struct instead (so only one per process). The procs file writer does a down_write(&tsk->sighand->fork_sem), and cgroup_fork() can do a down_read(¤t->sighand->fork_sem) if flags&CLONE_SIGHAND. If you put it as the second member of sighand_struct, there wouldn't even be any extra cacheline bouncing in the common case, since copy_sighand() would already have brought that line into cache in order to do atomic_inc(¤t->sighand->count) Paul _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
