The patch titled
Subject: mmap: add clarifying comment to vma_merge() code
has been added to the -mm mm-unstable branch. Its filename is
mmap-add-clarifying-comment-to-vma_merge-code.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mmap-add-clarifying-comment-to-vma_merge-code.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
Subject: mmap: add clarifying comment to vma_merge() code
Date: Fri, 29 Sep 2023 14:30:41 -0400
When tracing through the code in vma_merge(), it was not completely
clear why the error return to a dup_anon_vma() call would not overwrite
a previous attempt to the same function. This commit adds a comment
specifying why it is safe.
Link: https://lkml.kernel.org/r/20230929183041.2835469-4-Liam.Howlett@xxxxxxxxxx
Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
Suggested-by: Jann Horn <jannh@xxxxxxxxxx>
Link: https://lore.kernel.org/linux-mm/CAG48ez3iDwFPR=Ed1BfrNuyUJPMK_=StjxhUsCkL6po1s7bONg@xxxxxxxxxxxxxx/
Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx>
Cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Suren Baghdasaryan <surenb@xxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mmap.c | 5 +++++
1 file changed, 5 insertions(+)
--- a/mm/mmap.c~mmap-add-clarifying-comment-to-vma_merge-code
+++ a/mm/mmap.c
@@ -943,6 +943,11 @@ struct vm_area_struct *vma_merge(struct
vma_start_write(curr);
remove = curr;
remove2 = next;
+ /*
+ * Note that the dup_anon_vma below cannot overwrite err
+ * since the first caller would do nothing unless next
+ * has an anon_vma.
+ */
if (!next->anon_vma)
err = dup_anon_vma(prev, curr, &anon_dup);
}
_
Patches currently in -mm which might be from Liam.Howlett@xxxxxxxxxx are
maple_tree-add-mas_active-to-detect-in-tree-walks.patch
maple_tree-add-mas_underflow-and-mas_overflow-states.patch
mm-mempolicy-fix-set_mempolicy_home_node-previous-vma-pointer.patch
mmap-fix-vma_iterator-in-error-path-of-vma_merge.patch
mmap-fix-error-paths-with-dup_anon_vma.patch
mmap-add-clarifying-comment-to-vma_merge-code.patch
