On Fri, Oct 22, 2021 at 10:38 AM Yang Shi <shy828301@xxxxxxxxx> wrote: > > On Fri, Oct 22, 2021 at 4:16 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote: > > > > On Fri, Oct 22, 2021 at 09:46:19AM +0200, Andrea Righi wrote: > > > copy_huge_page() can be called with mapping->private_lock held from > > > __buffer_migrate_page() -> migrate_page_copy(), so it is not safe to > > > do a cond_resched() in this context. > > > > > > Introduce migrate_page_copy_nowait() and copy_huge_page_nowait() > > > variants that can be used from an atomic context. > > > > I think this is a consequence of THPs being created when they should not > > be. This is the wrong way to fix this problem; and I suspect it may > > already be fixed at least in -mm. We should have taken this path: > > > > if (!page_has_buffers(page)) > > return migrate_page(mapping, newpage, page, mode); > > > > but since we didn't, we can infer that there's a THP which has buffers > > (this should never occur). It's the same root cause as the invalidatepage > > problem, just with a very different signature. > > Yeah, exactly. And I replied to that syzbot report a few days ago > (https://lore.kernel.org/linux-mm/CAHbLzkoFaowaG8AU6tg_WMPdjcAdyE+Wafs7TJz1Z23TRg_d8A@xxxxxxxxxxxxxx/) > with the same conclusion. > > I'm not sure why Hugh didn't submit his patch, maybe he was waiting > for the test result from the bug reporter of that invalidatepage > issue? It should be fine, the fix is quite straightforward IMHO. Anyway if Hugh doesn't have time to do it, I could prepare the patch for formal review. > > >
