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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 2/20/25 22:48, David Hildenbrand wrote: > On 20.02.25 00:13, Balbir Singh wrote: >> page_pgmap() is referenced before checking if the page is a zone >> device page and this triggers the warning in page_pgmap(). Refactor >> the code to use the helper function after relevant checks. >> >> Cc: Alistair Popple >> Cc: Jason Gunthorpe >> Cc: David Hildenbrand >> Cc: Dan Williams >> >> Signed-off-by: Balbir Singh >> --- >> >> Fixes: 7f1cfd71153b ("mm: allow compound zone device pages") on >> mm-unstable > > Is there actually something broken? At least for now, reading folio->pgmap should just work, although it might be garbage. > It triggers the VM_WARN_ON_ONCE_PAGE static inline struct dev_pagemap *page_pgmap(const struct page *page) { VM_WARN_ON_ONCE_PAGE(!is_zone_device_page(page), page); return page_folio(page)->pgmap; } Nothing is broken, because the code below has checks for is_device_coherent_page(), but in general I think the WARN_ON is correct because it warns us against garbage and it's propagation if the correct checks are not in place. >> >>   mm/migrate_device.c | 13 ++++++++----- >>   1 file changed, 8 insertions(+), 5 deletions(-) >> >> diff --git a/mm/migrate_device.c b/mm/migrate_device.c >> index 6771893d4601..e0bf771edb6f 100644 >> --- a/mm/migrate_device.c >> +++ b/mm/migrate_device.c >> @@ -153,14 +153,17 @@ static int migrate_vma_collect_pmd(pmd_t *pmdp, >>                   goto next; >>               } >>               page = vm_normal_page(migrate->vma, addr, pte); >> -            pgmap = page_pgmap(page); >>               if (page && !is_zone_device_page(page) && >>                   !(migrate->flags & MIGRATE_VMA_SELECT_SYSTEM)) >>                   goto next; >> -            else if (page && is_device_coherent_page(page) && >> -                (!(migrate->flags & MIGRATE_VMA_SELECT_DEVICE_COHERENT) || >> -                 pgmap->owner != migrate->pgmap_owner)) >> -                goto next; >> +            else if (page && is_device_coherent_page(page)) { >> +                pgmap = page_pgmap(page); >> + >> +                if (!(migrate->flags & >> +                    MIGRATE_VMA_SELECT_DEVICE_COHERENT) || >> +                    pgmap->owner != migrate->pgmap_owner) >> +                    goto next; >> +            } > > Coding style wants you to use > > if () { > > } else if { > > } > > Not > > if () > else if { > > } > Ack, checkpatch.pl missed it, but agreed > > Something simpler might be > > page_pgmap(page)->owner != migrate->pgmap_owner > Yep, I had that and dropped it, the four clauses made it feel that it might benefit from a split. >>               mpfn = migrate_pfn(pfn) | MIGRATE_PFN_MIGRATE; >>               mpfn |= pte_write(pte) ? MIGRATE_PFN_WRITE : 0; >>           } > > Thanks for the review! Balbir