linux-kernel - [RFC PATCH 1/5] mm/mmap: Correctly position vma_iterator in __split

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Date: Fri, 31 May 2024 12:32:13 -0400
From: "Liam R. Howlett" <Liam.Howlett@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>,
        Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc: Vlastimil Babka <vbabka@...e.cz>, sidhartha.kumar@...cle.com,
        Matthew Wilcox <willy@...radead.org>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        linux-fsdevel@...r.kernel.org, bpf@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: [RFC PATCH 1/5] mm/mmap: Correctly position vma_iterator in __split_vma()

The vma iterator may be left pointing to the newly created vma.  This
happens when inserting the new vma at the end of the old vma
(!new_below).

The incorrect position in the vma iterator is not exposed currently
since the vma iterator is repositioned in the munmap path and is not
reused in any of the other paths.

This has limited impact in the current code, but is required for future
changes.

Fixes: b2b3b886738f ("mm: don't use __vma_adjust() in __split_vma()")
Signed-off-by: Liam R. Howlett <Liam.Howlett@...cle.com>
---
 mm/mmap.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/mm/mmap.c b/mm/mmap.c
index 83b4682ec85c..31d464e6a656 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2442,6 +2442,9 @@ static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma,
 	/* Success. */
 	if (new_below)
 		vma_next(vmi);
+	else
+		vma_prev(vmi);
+
 	return 0;
 
 out_free_mpol:
-- 
2.43.0