linux-kernel - Re: [PATCH v1] mm/mempolicy: fix migrate_to_node() assuming there is at least one VMA in a MM

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Message-Id: <20241121221937.c41ee2b5e8534729e94fc104@linux-foundation.org>
Date: Thu, 21 Nov 2024 22:19:37 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: "Liam R. Howlett" <Liam.Howlett@...cle.com>
Cc: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, syzbot+3511625422f7aa637f0d@...kaller.appspotmail.com,
 stable@...r.kernel.org, Christoph Lameter <cl@...ux.com>
Subject: Re: [PATCH v1] mm/mempolicy: fix migrate_to_node() assuming there
 is at least one VMA in a MM

On Wed, 20 Nov 2024 15:27:46 -0500 "Liam R. Howlett" <Liam.Howlett@...cle.com> wrote:

> I hate the extra check because syzbot can cause this as this should
> basically never happen in real life, but it seems we have to add it.

So..

--- a/mm/mempolicy.c~mm-mempolicy-fix-migrate_to_node-assuming-there-is-at-least-one-vma-in-a-mm-fix
+++ a/mm/mempolicy.c
@@ -1080,7 +1080,7 @@ static long migrate_to_node(struct mm_st

 	mmap_read_lock(mm);
 	vma = find_vma(mm, 0);
-	if (!vma) {
+	if (unlikely(!vma)) {
 		mmap_read_unlock(mm);
 		return 0;
 	}
_

?