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Wed, 27 Sep 2023 16:09:10 +0000 From: "Liam R. Howlett" To: Andrew Morton Cc: maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jann Horn , Lorenzo Stoakes , Vlastimil Babka , Suren Baghdasaryan , Matthew Wilcox , "Liam R. Howlett" Subject: [PATCH 3/3] mmap: Add clarifying comment to vma_merge() code Date: Wed, 27 Sep 2023 12:07:46 -0400 Message-Id: <20230927160746.1928098-4-Liam.Howlett@oracle.com> X-Mailer: git-send-email 2.40.1 In-Reply-To: <20230927160746.1928098-1-Liam.Howlett@oracle.com> References: <20230927160746.1928098-1-Liam.Howlett@oracle.com> X-ClientProxiedBy: YT4PR01CA0467.CANPRD01.PROD.OUTLOOK.COM (2603:10b6:b01:d6::23) To SN6PR10MB3022.namprd10.prod.outlook.com (2603:10b6:805:d8::25) MIME-Version: 1.0 X-MS-PublicTrafficType: Email X-MS-TrafficTypeDiagnostic: SN6PR10MB3022:EE_|IA1PR10MB6122:EE_ X-MS-Office365-Filtering-Correlation-Id: 5907b717-65c9-4527-0bc2-08dbbf7415bb X-MS-Exchange-SenderADCheck: 1 X-MS-Exchange-AntiSpam-Relay: 0 X-Microsoft-Antispam: BCL:0; X-Microsoft-Antispam-Message-Info: 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 X-Forefront-Antispam-Report: CIP:255.255.255.255;CTRY:;LANG:en;SCL:1;SRV:;IPV:NLI;SFV:NSPM;H:SN6PR10MB3022.namprd10.prod.outlook.com;PTR:;CAT:NONE;SFS:(13230031)(346002)(136003)(376002)(39860400002)(366004)(396003)(230922051799003)(1800799009)(451199024)(186009)(66946007)(66556008)(66476007)(38100700002)(6916009)(54906003)(478600001)(86362001)(2906002)(316002)(6666004)(36756003)(4744005)(5660300002)(8936002)(4326008)(26005)(966005)(2616005)(8676002)(1076003)(107886003)(41300700001)(6512007)(6506007)(6486002);DIR:OUT;SFP:1101; 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Wed, 27 Sep 2023 09:09:39 -0700 (PDT) X-getmail-retrieved-from-mailbox: INBOX X-GMAIL-THRID: 1778227628992234052 X-GMAIL-MSGID: 1778227628992234052 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. Suggested-by: Jann Horn Link: https://lore.kernel.org/linux-mm/CAG48ez3iDwFPR=Ed1BfrNuyUJPMK_=StjxhUsCkL6po1s7bONg@mail.gmail.com/ Signed-off-by: Liam R. Howlett --- mm/mmap.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/mmap.c b/mm/mmap.c index 2f0ee489db8a..3c78afb707cf 100644 --- a/mm/mmap.c +++ b/mm/mmap.c @@ -937,6 +937,11 @@ 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); }