linux-kernel - [PATCH v2 10/15] mm/mmap: Reposition vma iterator in mmap

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Date: Tue, 25 Jun 2024 15:11:40 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>
Cc: Suren Baghdasaryan <surenb@...gle.com>, Vlastimil Babka <vbabka@...e.cz>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Matthew Wilcox <willy@...radead.org>, sidhartha.kumar@...cle.com,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Bert Karwatzki <spasswolf@....de>, Jiri Olsa <olsajiri@...il.com>,
        linux-kernel@...r.kernel.org, Kees Cook <kees@...nel.org>,
        "Liam R. Howlett" <Liam.Howlett@...cle.com>
Subject: [PATCH v2 10/15] mm/mmap: Reposition vma iterator in mmap_region()

From: "Liam R. Howlett" <Liam.Howlett@...cle.com>

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.

Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 28 ++++++++++++++--------------
 1 file changed, 14 insertions(+), 14 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index f5b33de4e717..ecf55d32e804 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2963,11 +2963,12 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 		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);
 	}
 
 	/*
@@ -2980,11 +2981,8 @@ 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 */
@@ -3005,19 +3003,21 @@ 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);
 	}
 
-	/* 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:
 
 	/*
-- 
2.43.0