Re: [question] Panic in dax_writeback_one

[Dan Williams]

On Thu, Mar 11, 2021 at 4:20 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Thu, Mar 11, 2021 at 07:48:25AM +0000, chenjun (AM) wrote:
> > static int dax_writeback_one(struct xa_state *xas, struct dax_device
> > *dax_dev, struct address_space *mapping, void *entry)
> > ----dax_flush(dax_dev, page_address(pfn_to_page(pfn)), count * PAGE_SIZE);
> > The pfn is returned by the driver. In my case, the pfn does not have
> > struct page. so pfn_to_page(pfn) return a wrong address.
>
> I wasn't involved, but I think the right solution here is simply to
> replace page_address(pfn_to_page(pfn)) with pfn_to_virt(pfn).  I don't
> know why Dan decided to do this in the more complicated way.

pfn_to_virt() only works for the direct-map. If pages are not mapped I
don't see how pfn_to_virt() is expected to work.

The real question Chenjun is why are you writing a new simulator of
memory as a block-device vs reusing the pmem driver or brd?