From: Liam R. Howlett <Liam.Howlett@oracle.com>
Date: Fri, 29 Sep 2023 18:30:41 +0000 (-0400)
Subject: mmap: add clarifying comment to vma_merge() code
X-Git-Tag: v6.7-rc6-pxa1908~289^2~170
X-Git-Url: https://git.dujemihanovic.xyz/?a=commitdiff_plain;h=9a12d103f7d2d524f5e3d4358b9a9c03e4a9f1d2;p=linux.git

mmap: add clarifying comment to vma_merge() code

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@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Suggested-by: Jann Horn <jannh@google.com>
Link: https://lore.kernel.org/linux-mm/CAG48ez3iDwFPR=Ed1BfrNuyUJPMK_=StjxhUsCkL6po1s7bONg@mail.gmail.com/
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/mm/mmap.c b/mm/mmap.c
index 011ba48d9e72..673429ee8a9e 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -943,6 +943,11 @@ struct vm_area_struct *vma_merge(struct vma_iterator *vmi, struct mm_struct *mm,
 			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);
 		}