Re: [rfc] "fair" rw spinlocks

[Peter Zijlstra <peterz@infradead.org>]

On Mon, 2009-11-30 at 22:12 +0100, Thomas Gleixner wrote:

> I think the conversion Linus proposed is pretty feasible. I went
> through the read_lock sites and most of them are protecting function
> calls which we already use under rcu_read_lock() in other places like
> find_task* and thread or pid iterators.
> 
> There are a few non obvious ones in signal.c and posix-cpu-timers.c
> (what a surprise) but nothing looks too scary.
> 
> If nobody beats me I'm going to let sed loose on the kernel, lift the
> task_struct rcu free code from -rt and figure out what explodes.

Things like sched.c:tg_set_bandwidth() take the tasklist_lock in
read-mode to exclude tasks being added concurrently to avoid
sched_rt_can_attach() races with tg_has_rt_tasks().

Possibly the cgroup stuff has a smaller lock to use for this.