Re: [PATCH] mm/dmapool.c: add WARN_ON() in dma_pool_destroy

[Matthew Wilcox]

On Fri, Jul 31, 2020 at 01:32:15PM -0700, Andrew Morton wrote:
> On Fri, 31 Jul 2020 03:38:58 +0100 Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> 
> > On Fri, Jul 31, 2020 at 10:39:39AM +0800, qiang.zhang@xxxxxxxxxxxxx wrote:
> > > The pool is being destroyed, all page which in the pool,
> > > should be free. if some page is still be use by somebody,
> > > we should not just output error logs, also should also add
> > > a warning message.
> > 
> > There's already a warning message.  What value does this actually have?
> 
> Presumably so we get a backtrace in order to identify the errant
> caller.  

The existing message includes the name of the pool.  We don't typically
have more than one place that destroys a pool.

What might be helpful would be something that said who allocated and
didn't free the object, but again, there's typically only one place which
allocates from any given pool, so even that would be all that helpful.

I'm not particularly impressed by these patches which don't actually
justify themselves.