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Message-ID: <20250604140544.688711-1-david@redhat.com>
Date: Wed, 4 Jun 2025 16:05:44 +0200
From: David Hildenbrand <david@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: linux-mm@...ck.org,
David Hildenbrand <david@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
"Liam R. Howlett" <Liam.Howlett@...cle.com>,
Vlastimil Babka <vbabka@...e.cz>,
Mike Rapoport <rppt@...nel.org>,
Suren Baghdasaryan <surenb@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Jason Gunthorpe <jgg@...pe.ca>,
John Hubbard <jhubbard@...dia.com>,
Peter Xu <peterx@...hat.com>
Subject: [PATCH v1] 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.
Cc: Andrew Morton <akpm@...ux-foundation.org>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: Vlastimil Babka <vbabka@...e.cz>
Cc: Mike Rapoport <rppt@...nel.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>
Cc: Michal Hocko <mhocko@...e.com>
Cc: Jason Gunthorpe <jgg@...pe.ca>
Cc: John Hubbard <jhubbard@...dia.com>
Cc: Peter Xu <peterx@...hat.com>
Signed-off-by: David Hildenbrand <david@...hat.com>
---
Wanted to do this for a long time, but my todo list keeps growing ...
Based on mm/mm-unstable
---
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 e065a49842a87..3c3931fcdd820 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_PAGE(!PageAnonExclusive(&folio->page), page);
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 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
ret = mmap_read_lock_killable(mm);
if (ret) {
- BUG_ON(ret > 0);
if (!pages_done)
pages_done = ret;
break;
@@ -1819,11 +1815,11 @@ static __always_inline long __get_user_pages_locked(struct mm_struct *mm,
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);
/*
@@ -2908,7 +2904,8 @@ 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);
base-commit: 2d0c297637e7d59771c1533847c666cdddc19884
--
2.49.0
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