Re: [syzbot] [mm?] WARNING in __folio_rmap_sanity_checks (2)

Hillf Danton
2024-12-31T08:41:13Z

On Fri, 27 Dec 2024 20:56:21 -0800
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 8155b4ef3466 Add linux-next specific files for 20241220
> git tree: linux-next
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1652fadf980000

#syz test

--- x/mm/filemap.c
+++ y/mm/filemap.c
@@ -3636,6 +3636,10 @@ static vm_fault_t filemap_map_folio_rang
continue;
skip:
if (count) {
+ for (unsigned int i = 0; i < count; i++) {
+ if (page_folio(page + i) != folio)
+ goto out;
+ }
set_pte_range(vmf, folio, page, count, addr);
*rss += count;
folio_ref_add(folio, count);
@@ -3658,6 +3662,7 @@ skip:
ret = VM_FAULT_NOPAGE;
}

+out:
vmf->pte = old_ptep;

return ret;
@@ -3702,7 +3707,7 @@ vm_fault_t filemap_map_pages(struct vm_f
struct file *file = vma->vm_file;
struct address_space *mapping = file->f_mapping;
pgoff_t file_end, last_pgoff = start_pgoff;
- unsigned long addr;
+ unsigned long addr, pmd_end;
XA_STATE(xas, &mapping->i_pages, start_pgoff);
struct folio *folio;
vm_fault_t ret = 0;
@@ -3731,6 +3736,12 @@ vm_fault_t filemap_map_pages(struct vm_f
if (end_pgoff > file_end)
end_pgoff = file_end;

+ /* make vmf->pte[x] valid */
+ pmd_end = ALIGN(addr, PMD_SIZE);
+ pmd_end = (pmd_end - addr) >> PAGE_SHIFT;
+ if (end_pgoff - start_pgoff > pmd_end)
+ end_pgoff = start_pgoff + pmd_end;
+
folio_type = mm_counter_file(folio);
do {
unsigned long end;
--