Hello Alistair Popple,
The patch b05a79d4377f: "mm/gup: migrate device coherent pages when
pinning instead of failing" from Jul 15, 2022, leads to the following
Smatch static checker warning:
mm/migrate_device.c:842 migrate_device_coherent_page()
warn: duplicate check 'src_pfn & (1 << 1)' (previous on line 832)
mm/migrate_device.c
810 int migrate_device_coherent_page(struct page *page)
811 {
812 unsigned long src_pfn, dst_pfn = 0;
813 struct migrate_vma args;
814 struct page *dpage;
815
816 WARN_ON_ONCE(PageCompound(page));
817
818 lock_page(page);
819 src_pfn = migrate_pfn(page_to_pfn(page)) | MIGRATE_PFN_MIGRATE;
820 args.src = &src_pfn;
821 args.dst = &dst_pfn;
822 args.cpages = 1;
823 args.npages = 1;
824 args.vma = NULL;
825
826 /*
827 * We don't have a VMA and don't need to walk the page tables to find
828 * the source page. So call migrate_vma_unmap() directly to unmap the
829 * page as migrate_vma_setup() will fail if args.vma == NULL.
830 */
831 migrate_vma_unmap(&args);
832 if (!(src_pfn & MIGRATE_PFN_MIGRATE))
833 return -EBUSY;
Return here.
834
835 dpage = alloc_page(GFP_USER | __GFP_NOWARN);
836 if (dpage) {
837 lock_page(dpage);
838 dst_pfn = migrate_pfn(page_to_pfn(dpage));
839 }
840
841 migrate_vma_pages(&args);
--> 842 if (src_pfn & MIGRATE_PFN_MIGRATE)
843 copy_highpage(dpage, page);
No need to check again. Was dst_pfn intended?
844 migrate_vma_finalize(&args);
845
846 if (src_pfn & MIGRATE_PFN_MIGRATE)
847 return 0;
Same check again.
848 return -EBUSY;
849 }
regards,
dan carpenter
