mm/mmap: remove __vma_adjust()

Inline the work of __vma_adjust() into vma_merge().  This reduces code
size and has the added benefits of the comments for the cases being
located with the code.

Change the comments referencing vma_adjust() accordingly.

[Liam.Howlett@oracle.com: fix vma_merge() offset when expanding the next vma]
  Link: https://lkml.kernel.org/r/20230130195713.2881766-1-Liam.Howlett@oracle.com
Link: https://lkml.kernel.org/r/20230120162650.984577-49-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 97 insertions, 153 deletions

diff --git a/mm/mmap.c b/mm/mmap.c
index 604ba8293a95..8ce4cee42dce 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -741,133 +741,6 @@ int vma_shrink(struct vma_iterator *vmi, struct vm_area_struct *vma,
 }
 
 /*
- * We cannot adjust vm_start, vm_end, vm_pgoff fields of a vma that
- * is already present in an i_mmap tree without adjusting the tree.
- * The following helper function should be used when such adjustments
- * are necessary.  The "insert" vma (if any) is to be inserted
- * before we drop the necessary locks.
- */
-int __vma_adjust(struct vma_iterator *vmi, struct vm_area_struct *vma,
-	unsigned long start, unsigned long end, pgoff_t pgoff,
-	struct vm_area_struct *expand)
-{
-	struct mm_struct *mm = vma->vm_mm;
-	struct vm_area_struct *remove2 = NULL;
-	struct vm_area_struct *remove = NULL;
-	struct vm_area_struct *next = find_vma(mm, vma->vm_end);
-	struct vm_area_struct *orig_vma = vma;
-	struct file *file = vma->vm_file;
-	bool vma_changed = false;
-	long adjust_next = 0;
-	struct vma_prepare vma_prep;
-
-	if (next) {
-		int error = 0;
-
-		if (end >= next->vm_end) {
-			/*
-			 * vma expands, overlapping all the next, and
-			 * perhaps the one after too (mprotect case 6).
-			 * The only other cases that gets here are
-			 * case 1, case 7 and case 8.
-			 */
-			if (next == expand) {
-				/*
-				 * The only case where we don't expand "vma"
-				 * and we expand "next" instead is case 8.
-				 */
-				VM_WARN_ON(end != next->vm_end);
-				/*
-				 * we're removing "vma" and that to do so we
-				 * swapped "vma" and "next".
-				 */
-				VM_WARN_ON(file != next->vm_file);
-				swap(vma, next);
-				remove = next;
-			} else {
-				VM_WARN_ON(expand != vma);
-				/*
-				 * case 1, 6, 7, remove next.
-				 * case 6 also removes the one beyond next
-				 */
-				remove = next;
-				if (end > next->vm_end)
-					remove2 = find_vma(mm, next->vm_end);
-
-				VM_WARN_ON(remove2 != NULL &&
-					   end != remove2->vm_end);
-			}
-
-			/*
-			 * If next doesn't have anon_vma, import from vma after
-			 * next, if the vma overlaps with it.
-			 */
-			if (remove != NULL && !next->anon_vma)
-				error = dup_anon_vma(vma, remove2);
-			else
-				error = dup_anon_vma(vma, remove);
-
-		} else if (end > next->vm_start) {
-			/*
-			 * vma expands, overlapping part of the next:
-			 * mprotect case 5 shifting the boundary up.
-			 */
-			adjust_next = (end - next->vm_start);
-			VM_WARN_ON(expand != vma);
-			error = dup_anon_vma(vma, next);
-		} else if (end < vma->vm_end) {
-			/*
-			 * vma shrinks, and !insert tells it's not
-			 * split_vma inserting another: so it must be
-			 * mprotect case 4 shifting the boundary down.
-			 */
-			adjust_next = -(vma->vm_end - end);
-			VM_WARN_ON(expand != next);
-			error = dup_anon_vma(next, vma);
-		}
-		if (error)
-			return error;
-	}
-
-	if (vma_iter_prealloc(vmi))
-		return -ENOMEM;
-
-	vma_adjust_trans_huge(orig_vma, start, end, adjust_next);
-
-	init_multi_vma_prep(&vma_prep, vma, adjust_next ? next : NULL, remove,
-			    remove2);
-	VM_WARN_ON(vma_prep.anon_vma && adjust_next && next->anon_vma &&
-		   vma_prep.anon_vma != next->anon_vma);
-
-	vma_prepare(&vma_prep);
-
-	if (start < vma->vm_start || end > vma->vm_end)
-		vma_changed = true;
-
-	vma->vm_start = start;
-	vma->vm_end = end;
-	vma->vm_pgoff = pgoff;
-
-	if (vma_changed)
-		vma_iter_store(vmi, vma);
-
-	if (adjust_next) {
-		next->vm_start += adjust_next;
-		next->vm_pgoff += adjust_next >> PAGE_SHIFT;
-		if (adjust_next < 0) {
-			WARN_ON_ONCE(vma_changed);
-			vma_iter_store(vmi, next);
-		}
-	}
-
-	vma_complete(&vma_prep, vmi, mm);
-	vma_iter_free(vmi);
-	validate_mm(mm);
-
-	return 0;
-}
-
-/*
  * If the vma has a ->close operation then the driver probably needs to release
  * per-vma resources, so we don't attempt to merge those.
  */
@@ -993,7 +866,7 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
  * It is important for case 8 that the vma NNNN overlapping the
  * region AAAA is never going to extended over XXXX. Instead XXXX must
  * be extended in region AAAA and NNNN must be removed. This way in
- * all cases where vma_merge succeeds, the moment vma_adjust drops the
+ * all cases where vma_merge succeeds, the moment vma_merge drops the
  * rmap_locks, the properties of the merged vma will be already
  * correct for the whole merged range. Some of those properties like
  * vm_page_prot/vm_flags may be accessed by rmap_walks and they must
@@ -1003,6 +876,12 @@ can_vma_merge_after(struct vm_area_struct *vma, unsigned long vm_flags,
  * or other rmap walkers (if working on addresses beyond the "end"
  * parameter) may establish ptes with the wrong permissions of NNNN
  * instead of the right permissions of XXXX.
+ *
+ * In the code below:
+ * PPPP is represented by *prev
+ * NNNN is represented by *mid (and possibly equal to *next)
+ * XXXX is represented by *next or not represented at all.
+ * AAAA is not represented - it will be merged or the function will return NULL
  */
 struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
 			struct vm_area_struct *prev, unsigned long addr,
@@ -1013,11 +892,19 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
 			struct anon_vma_name *anon_name)
 {
 	pgoff_t pglen = (end - addr) >> PAGE_SHIFT;
+	pgoff_t vma_pgoff;
 	struct vm_area_struct *mid, *next, *res = NULL;
+	struct vm_area_struct *vma, *adjust, *remove, *remove2;
 	int err = -1;
 	bool merge_prev = false;
 	bool merge_next = false;
+	bool vma_expanded = false;
+	struct vma_prepare vp;
+	unsigned long vma_end = end;
+	long adj_next = 0;
+	unsigned long vma_start = addr;
 
+	validate_mm(mm);
 	/*
 	 * We later require that vma->vm_flags == vm_flags,
 	 * so this tests vma->vm_flags & VM_SPECIAL, too.
@@ -1035,13 +922,17 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
 	VM_WARN_ON(mid && end > mid->vm_end);
 	VM_WARN_ON(addr >= end);
 
-	/* Can we merge the predecessor? */
-	if (prev && prev->vm_end == addr &&
-			mpol_equal(vma_policy(prev), policy) &&
-			can_vma_merge_after(prev, vm_flags,
-					    anon_vma, file, pgoff,
-					    vm_userfaultfd_ctx, anon_name)) {
-		merge_prev = true;
+	if (prev) {
+		res = prev;
+		vma = 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)
+		    && can_vma_merge_after(prev, vm_flags, anon_vma, file,
+				   pgoff, vm_userfaultfd_ctx, anon_name)) {
+			merge_prev = true;
+		}
 	}
 	/* Can we merge the successor? */
 	if (next && end == next->vm_start &&
@@ -1051,32 +942,85 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
 					     vm_userfaultfd_ctx, anon_name)) {
 		merge_next = true;
 	}
+
+	remove = remove2 = adjust = NULL;
 	/* 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)) {	 /* cases 1, 6 */
-		err = __vma_adjust(vmi, prev, prev->vm_start,
-					next->vm_end, prev->vm_pgoff, prev);
-		res = prev;
-	} else if (merge_prev) {			/* cases 2, 5, 7 */
-		err = __vma_adjust(vmi, prev, prev->vm_start,
-					end, prev->vm_pgoff, prev);
-		res = prev;
+	    is_mergeable_anon_vma(prev->anon_vma, next->anon_vma, NULL)) {
+		remove = mid;				/* case 1 */
+		vma_end = next->vm_end;
+		err = dup_anon_vma(res, remove);
+		if (mid != next) {			/* case 6 */
+			remove2 = next;
+			if (!remove->anon_vma)
+				err = dup_anon_vma(res, remove2);
+		}
+	} else if (merge_prev) {
+		err = 0;				/* case 2 */
+		if (mid && end > mid->vm_start) {
+			err = dup_anon_vma(res, mid);
+			if (end == mid->vm_end) {	/* case 7 */
+				remove = mid;
+			} else {			/* case 5 */
+				adjust = mid;
+				adj_next = (end - mid->vm_start);
+			}
+		}
 	} else if (merge_next) {
-		if (prev && addr < prev->vm_end)	/* case 4 */
-			err = __vma_adjust(vmi, prev, prev->vm_start,
-					addr, prev->vm_pgoff, next);
-		else					/* cases 3, 8 */
-			err = __vma_adjust(vmi, mid, addr, next->vm_end,
-					next->vm_pgoff - pglen, next);
 		res = next;
+		if (prev && addr < prev->vm_end) {	/* case 4 */
+			vma_end = addr;
+			adjust = mid;
+			adj_next = -(vma->vm_end - addr);
+			err = dup_anon_vma(res, adjust);
+		} else {
+			vma = next;			/* case 3 */
+			vma_start = addr;
+			vma_end = next->vm_end;
+			vma_pgoff = mid->vm_pgoff;
+			err = 0;
+			if (mid != next) {		/* case 8 */
+				remove = mid;
+				err = dup_anon_vma(res, remove);
+			}
+		}
 	}
 
-	/*
-	 * Cannot merge with predecessor or successor or error in __vma_adjust?
-	 */
+	/* Cannot merge or error in anon_vma clone */
 	if (err)
 		return NULL;
+
+	if (vma_iter_prealloc(vmi))
+		return NULL;
+
+	vma_adjust_trans_huge(vma, vma_start, vma_end, adj_next);
+	init_multi_vma_prep(&vp, vma, adjust, remove, remove2);
+	VM_WARN_ON(vp.anon_vma && adjust && adjust->anon_vma &&
+		   vp.anon_vma != adjust->anon_vma);
+
+	vma_prepare(&vp);
+	if (vma_start < vma->vm_start || vma_end > vma->vm_end)
+		vma_expanded = true;
+
+	vma->vm_start = vma_start;
+	vma->vm_end = vma_end;
+	vma->vm_pgoff = vma_pgoff;
+
+	if (vma_expanded)
+		vma_iter_store(vmi, vma);
+
+	if (adj_next) {
+		adjust->vm_start += adj_next;
+		adjust->vm_pgoff += adj_next >> PAGE_SHIFT;
+		if (adj_next < 0) {
+			WARN_ON(vma_expanded);
+			vma_iter_store(vmi, next);
+		}
+	}
+
+	vma_complete(&vp, vmi, mm);
+	vma_iter_free(vmi);
+	validate_mm(mm);
 	khugepaged_enter_vma(res, vm_flags);
 
 	if (res)