From 792b429db7e0217faf7bce9fe46e7708135cf83c Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Wed, 4 Jun 2025 16:05:44 +0200 Subject: [PATCH] mm/gup: remove (VM_)BUG_ONs Especially once we hit one of the assertions in sanity_check_pinned_pages(), observing follow-up assertions failing in other code can give good clues about what went wrong, so use VM_WARN_ON_ONCE instead. While at it, let's just convert all VM_BUG_ON to VM_WARN_ON_ONCE as well. Add one comment for the pfn_valid() check. We have to introduce VM_WARN_ON_ONCE_VMA() to make that fly. Drop the BUG_ON after mmap_read_lock_killable(), if that ever returns something > 0 we're in bigger trouble. Convert the other BUG_ON's into VM_WARN_ON_ONCE as well, they are in a similar domain "should never happen", but more reasonable to check for during early testing. [david@redhat.com: use the _FOLIO variant where possible, per Lorenzo] Link: https://lkml.kernel.org/r/844bd929-a551-48e3-a12e-285cd65ba580@redhat.com Link: https://lkml.kernel.org/r/20250604140544.688711-1-david@redhat.com Signed-off-by: David Hildenbrand Acked-by: Vlastimil Babka Reviewed-by: Suren Baghdasaryan Reviewed-by: Lorenzo Stoakes Acked-by: SeongJae Park Reviewed-by: Liam R. Howlett Acked-by: Michal Hocko Reviewed-by: John Hubbard Cc: Mike Rapoport Cc: Jason Gunthorpe Cc: Peter Xu Signed-off-by: Andrew Morton --- include/linux/mmdebug.h | 12 ++++++++++++ mm/gup.c | 41 +++++++++++++++++++---------------------- 2 files changed, 31 insertions(+), 22 deletions(-) diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h index a0a3894900ed4..14a45979cccc9 100644 --- a/include/linux/mmdebug.h +++ b/include/linux/mmdebug.h @@ -89,6 +89,17 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi); } \ unlikely(__ret_warn_once); \ }) +#define VM_WARN_ON_ONCE_VMA(cond, vma) ({ \ + static bool __section(".data..once") __warned; \ + int __ret_warn_once = !!(cond); \ + \ + if (unlikely(__ret_warn_once && !__warned)) { \ + dump_vma(vma); \ + __warned = true; \ + WARN_ON(1); \ + } \ + unlikely(__ret_warn_once); \ +}) #define VM_WARN_ON_VMG(cond, vmg) ({ \ int __ret_warn = !!(cond); \ \ @@ -115,6 +126,7 @@ void vma_iter_dump_tree(const struct vma_iterator *vmi); #define VM_WARN_ON_FOLIO(cond, folio) BUILD_BUG_ON_INVALID(cond) #define VM_WARN_ON_ONCE_FOLIO(cond, folio) BUILD_BUG_ON_INVALID(cond) #define VM_WARN_ON_ONCE_MM(cond, mm) BUILD_BUG_ON_INVALID(cond) +#define VM_WARN_ON_ONCE_VMA(cond, vma) BUILD_BUG_ON_INVALID(cond) #define VM_WARN_ON_VMG(cond, vmg) BUILD_BUG_ON_INVALID(cond) #define VM_WARN_ONCE(cond, format...) BUILD_BUG_ON_INVALID(cond) #define VM_WARN(cond, format...) BUILD_BUG_ON_INVALID(cond) diff --git a/mm/gup.c b/mm/gup.c index 3c39cbbeebef1..7f2644a433a0f 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -64,11 +64,11 @@ static inline void sanity_check_pinned_pages(struct page **pages, !folio_test_anon(folio)) continue; if (!folio_test_large(folio) || folio_test_hugetlb(folio)) - VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page), page); + VM_WARN_ON_ONCE_FOLIO(!PageAnonExclusive(&folio->page), folio); else /* Either a PTE-mapped or a PMD-mapped THP. */ - VM_BUG_ON_PAGE(!PageAnonExclusive(&folio->page) && - !PageAnonExclusive(page), page); + VM_WARN_ON_ONCE_PAGE(!PageAnonExclusive(&folio->page) && + !PageAnonExclusive(page), page); } } @@ -760,8 +760,8 @@ static struct page *follow_huge_pmd(struct vm_area_struct *vma, if (!pmd_write(pmdval) && gup_must_unshare(vma, flags, page)) return ERR_PTR(-EMLINK); - VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) && - !PageAnonExclusive(page), page); + VM_WARN_ON_ONCE_PAGE((flags & FOLL_PIN) && PageAnon(page) && + !PageAnonExclusive(page), page); ret = try_grab_folio(page_folio(page), 1, flags); if (ret) @@ -899,8 +899,8 @@ static struct page *follow_page_pte(struct vm_area_struct *vma, goto out; } - VM_BUG_ON_PAGE((flags & FOLL_PIN) && PageAnon(page) && - !PageAnonExclusive(page), page); + VM_WARN_ON_ONCE_PAGE((flags & FOLL_PIN) && PageAnon(page) && + !PageAnonExclusive(page), page); /* try_grab_folio() does nothing unless FOLL_GET or FOLL_PIN is set. */ ret = try_grab_folio(folio, 1, flags); @@ -1180,7 +1180,7 @@ static int faultin_page(struct vm_area_struct *vma, if (unshare) { fault_flags |= FAULT_FLAG_UNSHARE; /* FAULT_FLAG_WRITE and FAULT_FLAG_UNSHARE are incompatible */ - VM_BUG_ON(fault_flags & FAULT_FLAG_WRITE); + VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_WRITE); } ret = handle_mm_fault(vma, address, fault_flags, NULL); @@ -1760,10 +1760,7 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm, } /* VM_FAULT_RETRY or VM_FAULT_COMPLETED cannot return errors */ - if (!*locked) { - BUG_ON(ret < 0); - BUG_ON(ret >= nr_pages); - } + VM_WARN_ON_ONCE(!*locked && (ret < 0 || ret >= nr_pages)); if (ret > 0) { nr_pages -= ret; @@ -1808,7 +1805,6 @@ retry: ret = mmap_read_lock_killable(mm); if (ret) { - BUG_ON(ret > 0); if (!pages_done) pages_done = ret; break; @@ -1819,11 +1815,11 @@ retry: pages, locked); if (!*locked) { /* Continue to retry until we succeeded */ - BUG_ON(ret != 0); + VM_WARN_ON_ONCE(ret != 0); goto retry; } if (ret != 1) { - BUG_ON(ret > 1); + VM_WARN_ON_ONCE(ret > 1); if (!pages_done) pages_done = ret; break; @@ -1885,10 +1881,10 @@ long populate_vma_page_range(struct vm_area_struct *vma, int gup_flags; long ret; - VM_BUG_ON(!PAGE_ALIGNED(start)); - VM_BUG_ON(!PAGE_ALIGNED(end)); - VM_BUG_ON_VMA(start < vma->vm_start, vma); - VM_BUG_ON_VMA(end > vma->vm_end, vma); + VM_WARN_ON_ONCE(!PAGE_ALIGNED(start)); + VM_WARN_ON_ONCE(!PAGE_ALIGNED(end)); + VM_WARN_ON_ONCE_VMA(start < vma->vm_start, vma); + VM_WARN_ON_ONCE_VMA(end > vma->vm_end, vma); mmap_assert_locked(mm); /* @@ -1957,8 +1953,8 @@ long faultin_page_range(struct mm_struct *mm, unsigned long start, int gup_flags; long ret; - VM_BUG_ON(!PAGE_ALIGNED(start)); - VM_BUG_ON(!PAGE_ALIGNED(end)); + VM_WARN_ON_ONCE(!PAGE_ALIGNED(start)); + VM_WARN_ON_ONCE(!PAGE_ALIGNED(end)); mmap_assert_locked(mm); /* @@ -2914,7 +2910,8 @@ static int gup_fast_pte_range(pmd_t pmd, pmd_t *pmdp, unsigned long addr, } else if (pte_special(pte)) goto pte_unmap; - VM_BUG_ON(!pfn_valid(pte_pfn(pte))); + /* If it's not marked as special it must have a valid memmap. */ + VM_WARN_ON_ONCE(!pfn_valid(pte_pfn(pte))); page = pte_page(pte); folio = try_grab_folio_fast(page, 1, flags); -- 2.47.2