On Fri, Dec 23, 2022 at 08:38:55AM -0800, Christoph Hellwig wrote:
> > @@ -280,14 +268,14 @@ void dma_pool_destroy(struct dma_pool *pool)
> > mutex_unlock(&pools_reg_lock);
> >
> > list_for_each_entry_safe(page, tmp, &pool->page_list, page_list) {
> > + if (!is_page_busy(page))
> > + dma_free_coherent(pool->dev, pool->allocation,
> > + page->vaddr, page->dma);
> > + else
> > dev_err(pool->dev, "%s %s, %p busy\n", __func__,
> > pool->name, page->vaddr);
> > + list_del(&page->page_list);
> > + kfree(page);
>
> Hmm. The is_page_busy case is really a should not happen case.
> What is the benefit of skipping the dma_free_coherent and leaking
> memory here, vs letting KASAN and friends see the free and possibly
> help with debugging? In other words, why is this not:
>
> WARN_ON_ONCE(is_page_busy(page));
> dma_free_coherent(pool->dev, pool->allocation, page->vaddr,
> page->dma);
> ...
The memory is presumed to still be owned by the device in this case, so
the kernel shouldn't free it. I don't think KASAN will be very helpful
if the device corrupts memory.
> > page->in_use--;
> > *(int *)vaddr = page->offset;
> > page->offset = offset;
> > - /*
> > - * Resist a temptation to do
> > - * if (!is_page_busy(page)) pool_free_page(pool, page);
> > - * Better have a few empty pages hang around.
> > - */
>
> This doesn't look related to the rest, or am I missing something?
Oops, this was supposed to go with a later patch in this series that
removed "is_page_busy()".
