linux-kernel - Re: [PATCH] mm: abort vma_modify() on merge out of memory failure

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Message-Id: <20250222172634.fecb3b5e5f74e310f4a94772@linux-foundation.org>
Date: Sat, 22 Feb 2025 17:26:34 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
Cc: "Liam R . Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka
 <vbabka@...e.cz>, Jann Horn <jannh@...gle.com>, linux-mm@...ck.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, Brad Spengler
 <brad.spengler@...nsrcsec.com>
Subject: Re: [PATCH] mm: abort vma_modify() on merge out of memory failure

On Sat, 22 Feb 2025 16:19:52 +0000 Lorenzo Stoakes <lorenzo.stoakes@...cle.com> wrote:

> The remainder of vma_modify() relies upon the vmg state remaining pristine
> after a merge attempt.
> 

This patch is against your "mm: simplify vma merge structure and expand
comments", presently in mm-unstable.  I tweaked things (simple) so it
applies to mainline:

--- a/mm/vma.c~mm-abort-vma_modify-on-merge-out-of-memory-failure
+++ a/mm/vma.c
@@ -1509,24 +1509,28 @@ int do_vmi_munmap(struct vma_iterator *v
 static struct vm_area_struct *vma_modify(struct vma_merge_struct *vmg)
 {
 	struct vm_area_struct *vma = vmg->vma;
+	unsigned long start = vmg->start;
+	unsigned long end = vmg->end;
 	struct vm_area_struct *merged;

 	/* First, try to merge. */
 	merged = vma_merge_existing_range(vmg);
 	if (merged)
 		return merged;
+	if (vmg_nomem(vmg))
+		return ERR_PTR(-ENOMEM);

 	/* Split any preceding portion of the VMA. */
-	if (vma->vm_start < vmg->start) {
-		int err = split_vma(vmg->vmi, vma, vmg->start, 1);
+	if (vma->vm_start < start) {
+		int err = split_vma(vmg->vmi, vma, start, 1);

 		if (err)
 			return ERR_PTR(err);
 	}

 	/* Split any trailing portion of the VMA. */
-	if (vma->vm_end > vmg->end) {
-		int err = split_vma(vmg->vmi, vma, vmg->end, 0);
+	if (vma->vm_end > end) {
+		int err = split_vma(vmg->vmi, vma, end, 0);

 		if (err)
 			return ERR_PTR(err);
_