Re: [Ksummit-discuss] [TECH TOPIC] Fix devm_kzalloc, its users, or both

[Tejun Heo <tj@kernel.org>]

Hello,

On Tue, Aug 04, 2015 at 01:56:38PM +0200, Daniel Vetter wrote:
> On Tue, Aug 4, 2015 at 1:18 PM, Russell King - ARM Linux
> <linux@arm.linux.org.uk> wrote:
> > A solution to that would be to drop something like a read-write lock into
> > almost all f_op methods, which sounds expensive to me in the general case.
> 
> srcu is what I considered since it would be least intrusive and shifts
> the overall all to the write. The problem of course is that if you do

percpu_ref is likely a better fit.

> that then there will be deadlock gallore - suddenly anything called
> from f->ops can stall code called from ->remove. And looking at how
> regularly we have lockdep splat in the driver unload code just in i915
> that will be really painful.

It's the other side of the same coin.  At least it's a lot easier to
detect with a lot more deterministic failure mode than derefing freed
memory or accessing gone hardware.

Thanks.

-- 
tejun