[v5.1,11/19] mm/mmap: Reposition vma iterator in mmap_region()

Commit Message

Bert Karwatzki Aug. 16, 2024, 11:13 a.m. UTC

Instead of moving (or leaving) the vma iterator pointing at the previous
vma, leave it pointing at the insert location.  Pointing the vma
iterator at the insert location allows for a cleaner walk of the vma
tree for MAP_FIXED and the no expansion cases.

The vma_prev() call in the case of merging the previous vma is
equivalent to vma_iter_prev_range(), since the vma iterator will be
pointing to the location just before the previous vma.

Signed-off-by: Liam R. Howlett <[e-mail]>
Reviewed-by: Lorenzo Stoakes <[e-mail]>
---
 mm/mmap.c | 38 ++++++++++++++++++++++----------------
 1 file changed, 22 insertions(+), 16 deletions(-)

--
2.45.2

Patch

diff --git a/mm/mmap.c b/mm/mmap.c
index 16fd14b243f9..6720b55b47ed 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1404,21 +1404,22 @@  unsigned long mmap_region(struct file *file, unsigned long addr,
 		mas_init(&mas_detach, &mt_detach, /* addr = */ 0);
 		/* Prepare to unmap any existing mapping in the area */
 		if (vms_gather_munmap_vmas(&vms, &mas_detach))
-			return -ENOMEM;
+			goto gather_failed;

 		/* Remove any existing mappings from the vma tree */
 		if (vma_iter_clear_gfp(&vmi, addr, end, GFP_KERNEL))
-			return -ENOMEM;
+			goto clear_tree_failed;

 		/* Unmap any existing mapping in the area */
 		vms_complete_munmap_vmas(&vms, &mas_detach);
 		next = vms.next;
 		prev = vms.prev;
-		vma_prev(&vmi);
 		vma = NULL;
 	} else {
 		next = vma_next(&vmi);
 		prev = vma_prev(&vmi);
+		if (prev)
+			vma_iter_next_range(&vmi);
 	}

 	/*
@@ -1431,11 +1432,8 @@  unsigned long mmap_region(struct file *file, unsigned long addr,
 		vm_flags |= VM_ACCOUNT;
 	}

-	if (vm_flags & VM_SPECIAL) {
-		if (prev)
-			vma_iter_next_range(&vmi);
+	if (vm_flags & VM_SPECIAL)
 		goto cannot_expand;
-	}

 	/* Attempt to expand an old mapping */
 	/* Check next */
@@ -1456,19 +1454,21 @@  unsigned long mmap_region(struct file *file, unsigned long addr,
 		merge_start = prev->vm_start;
 		vma = prev;
 		vm_pgoff = prev->vm_pgoff;
-	} else if (prev) {
-		vma_iter_next_range(&vmi);
+		vma_prev(&vmi); /* Equivalent to going to the previous range */
 	}

-	/* Actually expand, if possible */
-	if (vma &&
-	    !vma_expand(&vmi, vma, merge_start, merge_end, vm_pgoff, next)) {
-		khugepaged_enter_vma(vma, vm_flags);
-		goto expanded;
+	if (vma) {
+		/* Actually expand, if possible */
+		if (!vma_expand(&vmi, vma, merge_start, merge_end, vm_pgoff, next)) {
+			khugepaged_enter_vma(vma, vm_flags);
+			goto expanded;
+		}
+
+		/* If the expand fails, then reposition the vma iterator */
+		if (unlikely(vma == prev))
+			vma_iter_set(&vmi, addr);
 	}

-	if (vma == prev)
-		vma_iter_set(&vmi, addr);
 cannot_expand:

 	/*
@@ -1629,6 +1629,12 @@  unsigned long mmap_region(struct file *file, unsigned long addr,
 		vm_unacct_memory(charged);
 	validate_mm(mm);
 	return error;
+
+clear_tree_failed:
+	abort_munmap_vmas(&mas_detach);
+gather_failed:
+	validate_mm(mm);
+	return -ENOMEM;
 }

 static int __vm_munmap(unsigned long start, size_t len, bool unlock)