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mm/mmap/vma_merge: init cleanup, be explicit about the non-mergeable case 

Rather than setting err = -1 and only resetting if we hit merge cases,
explicitly check the non-mergeable case to make it abundantly clear that
we only proceed with the rest if something is mergeable, default err to 0
and only update if an error might occur.

Move the merge_prev, merge_next cases closer to the logic determining
curr, next and reorder initial variables so they are more logically
grouped.

This has no functional impact.

Link: https://lkml.kernel.org/r/99259fbc6403e80e270e1cc4612abbc8620b121b.1679516210.git.lstoakes@gmail.com
Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Cc: David Hildenbrand <david@redhat.com>
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Lorenzo Stoakes 2023-03-22 20:19:00 +00:00 committed by Andrew Morton
parent b0729ae0ae
commit 0173db4f7f
1 changed files with 23 additions and 26 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

49
mm/mmap.c
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@ -896,18 +896,18 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
struct vm_userfaultfd_ctx vm_userfaultfd_ctx,
struct anon_vma_name *anon_name)
{
pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
pgoff_t vma_pgoff;
struct vm_area_struct *curr, *next, *res;
struct vm_area_struct *vma, *adjust, *remove, *remove2;
int err = -1;
struct vma_prepare vp;
pgoff_t vma_pgoff;
int err = 0;
bool merge_prev = false;
bool merge_next = false;
bool vma_expanded = false;
struct vma_prepare vp;
unsigned long vma_end = end;
long adj_start = 0;
unsigned long vma_start = addr;
unsigned long vma_end = end;
pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
long adj_start = 0;
validate_mm(mm);
/*
@ -926,24 +926,14 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
else
next = NULL; /* case 5 */
/*
* 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 && (addr != curr->vm_start || end > curr->vm_end));
VM_WARN_ON(addr >= end);
if (prev) {
vma_start = prev->vm_start;
vma_pgoff = prev->vm_pgoff;
/* Can we merge the predecessor? */
if (prev->vm_end == addr && mpol_equal(vma_policy(prev), policy)
if (addr == prev->vm_end && mpol_equal(vma_policy(prev), policy)
&& can_vma_merge_after(prev, vm_flags, anon_vma, file,
pgoff, vm_userfaultfd_ctx, anon_name)) {
pgoff, vm_userfaultfd_ctx, anon_name)) {
merge_prev = true;
vma_prev(vmi);
}
@ -951,13 +941,22 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
/* Can we merge the successor? */
if (next && mpol_equal(policy, vma_policy(next)) &&
can_vma_merge_before(next, vm_flags,
anon_vma, file, pgoff+pglen,
can_vma_merge_before(next, vm_flags, anon_vma, file, pgoff+pglen,
vm_userfaultfd_ctx, anon_name)) {
merge_next = true;
}
if (!merge_prev && !merge_next)
return NULL; /* Not mergeable. */
res = vma = prev;
remove = remove2 = adjust = NULL;
/* Verify some invariant that must be enforced by the caller. */
VM_WARN_ON(prev && addr <= prev->vm_start);
VM_WARN_ON(curr && (addr != curr->vm_start || end > curr->vm_end));
VM_WARN_ON(addr >= end);
/* Can we merge both the predecessor and the successor? */
if (merge_prev && merge_next &&
is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) {
@ -970,8 +969,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
if (!next->anon_vma)
err = dup_anon_vma(prev, curr);
}
} else if (merge_prev) {
err = 0; /* case 2 */
} else if (merge_prev) { /* case 2 */
if (curr) {
err = dup_anon_vma(prev, curr);
if (end == curr->vm_end) { /* case 7 */
@ -981,7 +979,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
adj_start = (end - curr->vm_start);
}
}
} else if (merge_next) {
} else { /* merge_next */
res = next;
if (prev && addr < prev->vm_end) { /* case 4 */
vma_end = addr;
@ -997,7 +995,6 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
vma_start = addr;
vma_end = next->vm_end;
vma_pgoff = next->vm_pgoff;
err = 0;
if (curr) { /* case 8 */
vma_pgoff = curr->vm_pgoff;
remove = curr;
@ -1006,7 +1003,7 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
}
}
/* Cannot merge or error in anon_vma clone */
/* Error in anon_vma clone. */
if (err)
return NULL;