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U2FsdGVkX1+c5HiZAGqhuB4YKmIgvXn1aG+uLs2utCu00RbCuaDZReETCo41CZDudx/TG2MBk6T0KBRhnJUj/n8WV5zRD52REAo0YhXV7iwgLARvwnxpmhqenwNnzmk6U0jvaWYkWy3PzNAlg4c1/qwN3K8s0z08IjmSBKFPBmhBjBF9DgmZUDyNbRscYarMnrR9LJrymZSuInK0YD7Chi3/YSjcrZeREJUIxtx/4bYMGYil/iWJsU+QrKQg0WI+97YXKpV51q8IsLihcBcadVWeRE/LbBYb2Fm8u6juJeARn9qF8bI6tVDaWMddj1nzrzmFAssfVdP27J4LyL7nP9qtD+UzX0FbTe5iqmBQcBk+rknMGdKFX5Ygi111tssTlH22it1EL6CUeNxDsGNswT1dq9S3hVvBdksvpvw00Y/m5HaIGS/x2upq4RndygNEdghFf0jCAkCTnYYg7V7x/lLALy/z8VsVVupVis37GM8cTfJUFlBHD+PE8R5ZbzKV4vqJG05stSrrbiotqoOCxtnj5RunWSIH9w8iuQAazIP+8ZFTo16l3sGKnhW5ElbxLOROvUwE1D7/UsrAiR5WN/vsc3hXuYL1TPZ41v6zVKS3uETaJKHrAO/6Yc62t4D8GW83hTiNWulVcKi0XmWF2UGw7+UcN6pOW+wyLCidIAtWMG2w1c62hW77RVqLsqVk6v0EnaVj0hQFHDaI11OTKioe1H7AtPXaQD/mZ3uAMiX6CxMX671X6hfYw0mZMnlCqg/VtVlugM74BRTsuUmoWvctusVf3UPzA8V3Wi9s59MdXdBLEcvrOQNDS1HjTgeZeQfCGxBhD02ZLF8qIRr3SkeTfuppdDATVynk3y1e0505VbnwAdWdLKroVqRMpnH70xR/xAzfyM2EgfmoLsgfjWxP5Nu2b0g/u5Ab7gCzt61kYadb/zBAHSYtLniq78y8uJ4kfQtMJZPOdQVDGHl IpQtEa5t zPZ40hlWVRfx7s939vwicUx0BMkpgkxgcckVlfHmbrJX298YriFQjzUi8EYNz4lsZ7dFs7+so+B1zoVw= 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: List-Subscribe: List-Unsubscribe: On Mon, Jan 05, 2026 at 08:11:49PM +0000, Lorenzo Stoakes wrote: > The is_mergeable_anon_vma() function uses vmg->middle as the source > VMA. However when merging a new VMA, this field is NULL. > > In all cases except mremap(), the new VMA will either be newly established > and thus lack an anon_vma, or will be an expansion of an existing VMA thus > we do not care about whether VMA is CoW'd or not. > > In the case of an mremap(), we can end up in a situation where we can > accidentally allow an unfaulted/faulted merge with a VMA that has been > forked, violating the general rule that we do not permit this for reasons > of anon_vma lock scalability. > > Now we have the ability to be aware of the fact we are copying a VMA and > also know which VMA that is, we can explicitly check for this, so do so. > > This is pertinent since commit 879bca0a2c4f ("mm/vma: fix incorrectly > disallowed anonymous VMA merges"), as this patch permits unfaulted/faulted > merges that were previously disallowed running afoul of this issue. > > While we are here, vma_had_uncowed_parents() is a confusing name, so make > it simple and rename it to vma_is_fork_child(). > > Signed-off-by: Lorenzo Stoakes > Fixes: 879bca0a2c4f ("mm/vma: fix incorrectly disallowed anonymous VMA merges") > Cc: stable@kernel.org > --- LGTM, so: Reviewed-by: Harry Yoo -- Cheers, Harry / Hyeonggon