The patch titled
Subject: mm/mmap/vma_merge: extend invariants, avoid invalid res, vma
has been added to the -mm mm-unstable branch. Its filename is
mm-mmap-vma_merge-extend-invariants-avoid-invalid-res-vma.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-mmap-vma_merge-extend-invariants-avoid-invalid-res-vma.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Subject: mm/mmap/vma_merge: extend invariants, avoid invalid res, vma
Date: Sat, 18 Mar 2023 11:13:20 +0000
Previously, vma was an uninitialised variable which was only definitely
assigned as a result of the logic covering all possible input cases - for
it to have remained uninitialised, prev would have to be NULL, and next
would _have_ to be mergeable.
We now reuse vma to assign curr and next, so to be absolutely explicit,
ensure this variable is _always_ assigned, and while we're at it remove
the redundant assignment of both res and vma (if prev is NULL then we
simply assign to NULL).
In addition, we absolutely do rely on addr == curr->vm_start should curr
exist, so assert as much.
Link: https://lkml.kernel.org/r/0b7d3e6c770a2bdc2c307ddde268561135ef3395.1679137163.git.lstoakes@xxxxxxxxx
Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
--- a/mm/mmap.c~mm-mmap-vma_merge-extend-invariants-avoid-invalid-res-vma
+++ a/mm/mmap.c
@@ -911,7 +911,7 @@ struct vm_area_struct *vma_merge(struct
{
pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
pgoff_t vma_pgoff;
- struct vm_area_struct *curr, *next, *res = NULL;
+ struct vm_area_struct *curr, *next, *res;
struct vm_area_struct *vma, *adjust, *remove, *remove2;
int err = -1;
bool merge_prev = false;
@@ -978,14 +978,18 @@ struct vm_area_struct *vma_merge(struct
else
next = NULL;
- /* verify some invariant that must be enforced by the caller */
+ /*
+ * By default, we return prev. Cases 3, 4, 8 will instead return next
+ * and cases 3, 8 will also update vma to point at next.
+ */
+ res = vma = prev;
+
+ /* Verify some invariant that must be enforced by the caller. */
VM_WARN_ON(prev && addr <= prev->vm_start);
- VM_WARN_ON(curr && end > curr->vm_end);
+ VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));
VM_WARN_ON(addr >= end);
if (prev) {
- res = prev;
- vma = prev;
vma_start = prev->vm_start;
vma_pgoff = prev->vm_pgoff;
/* Can we merge the predecessor? */
@@ -996,6 +1000,7 @@ struct vm_area_struct *vma_merge(struct
vma_prev(vmi);
}
}
+
/* Can we merge the successor? */
if (next && mpol_equal(policy, vma_policy(next)) &&
can_vma_merge_before(next, vm_flags,
@@ -1036,6 +1041,10 @@ struct vm_area_struct *vma_merge(struct
adj_start = -(prev->vm_end - addr);
err = dup_anon_vma(next, prev);
} else {
+ /*
+ * Note that cases 3 and 8 are the ONLY ones where prev
+ * is permitted to be (but is not necessarily) NULL.
+ */
vma = next; /* case 3 */
vma_start = addr;
vma_end = next->vm_end;
_
Patches currently in -mm which might be from lstoakes@xxxxxxxxx are
mm-remove-unused-vmf_insert_mixed_prot.patch
mm-remove-vmf_insert_pfn_xxx_prot-for-huge-page-table-entries.patch
drm-ttm-remove-comment-referencing-now-removed-vmf_insert_mixed_prot.patch
mm-prefer-xxx_page-alloc-free-functions-for-order-0-pages.patch
mm-refactor-do_fault_around.patch
mm-pefer-fault_around_pages-to-fault_around_bytes.patch
mm-mmap-vma_merge-further-improve-prev-next-vma-naming.patch
mm-mmap-vma_merge-set-next-to-null-if-not-applicable.patch
mm-mmap-vma_merge-extend-invariants-avoid-invalid-res-vma.patch
mm-mmap-vma_merge-be-explicit-about-the-non-mergeable-case.patch
fs-proc-kcore-avoid-bounce-buffer-for-ktext-data.patch
mm-vmalloc-use-rwsem-mutex-for-vmap_area_lock-and-vmap_block-lock.patch
fs-proc-kcore-convert-read_kcore-to-read_kcore_iter.patch
mm-vmalloc-convert-vread-to-vread_iter.patch
