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Howlett" , Andrew Morton Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jann Horn , Lorenzo Stoakes , Suren Baghdasaryan , Matthew Wilcox References: <20230929183041.2835469-1-Liam.Howlett@oracle.com> <20230929183041.2835469-4-Liam.Howlett@oracle.com> From: Vlastimil Babka In-Reply-To: <20230929183041.2835469-4-Liam.Howlett@oracle.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 52C28120007 X-Stat-Signature: nt43h3zhcdsc5uqis6bicwbsz5a5upcp X-HE-Tag: 1696230696-352210 X-HE-Meta: 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 aWcqMh+Q JWAQquPChXEokWzkcRKT/1D/xCuy7hggaNw4/0BcvCE2w/S/zVmFlnBRhpJqbgvG8pxPSRLIdQJcQoWzvFCVqAfz8VmLs5g9jom74d+U8J2EGs56YNwA3AgVeeewmylRJ1r6QQ5Wn5EAtjoH4ACejPaV4wfYH1UJtF6r1OX/qz7IBWmBpN9/W99L6sCTNwcufZ2QxqYT91iWoPPuqRoHuqM5UReXKNZRue6fABTlMqX8jGVPySmwbAVMWk/QjQ4ijE/wOghiyMKmfSImakGCrP2nVuc7Rt9AiEy0eWMFIazKqj6+pIQWJhxshytA2caiaBv+RduP9JaV7TkGgb+23DJg+UaXSAMaeH/wzaPag6aEN8R7dsSbgAb0EXw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 9/29/23 20:30, Liam R. Howlett wrote: > 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 Acked-by: Vlastimil Babka > --- > mm/mmap.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index f9f0a5fe4db4..9967acbd070f 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); > }