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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 23:05, David Hildenbrand wrote: > On 20.02.25 12:58, Balbir Singh wrote: >> 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. > > Ah! Now I read your "triggers the warning in page_pgmap()" in the description. > > It's usually a good idea to just include the splat you observed, if you did, and call it "triggers the VM_WARN_ON_ONCE_PAGE". Sure > > The "Fixes:" should go above the "---" in that case. I was not sure if the commit-ids in mm-unstable are persistent, so I put it below the --- to avoid confusion > >> >> >>>> >>>>    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. > > Right, the mixture of && and || is confusing. > > > So with the {} > > Acked-by: David Hildenbrand > > Thanks! > Thanks, I can respin it with the {} as needed. Balbir