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Shutemov" , Mike Kravetz , Minchan Kim , Russell King , Thomas Bogendoerfer , Thomas Gleixner , Vishal Verma , Vlastimil Babka , Will Deacon , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH 5/6] mremap: Check if it's possible to split original vma Date: Tue, 13 Oct 2020 02:34:15 +0100 Message-Id: <20201013013416.390574-6-dima@arista.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20201013013416.390574-1-dima@arista.com> References: <20201013013416.390574-1-dima@arista.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable 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: If original VMA can't be split at the desired address, do_munmap() will fail and leave both new-copied VMA and old VMA. De-facto it's MREMAP_DONTUNMAP behaviour, which is unexpected. Currently, it may fail such way for hugetlbfs and dax device mappings. Minimize such unpleasant situations to OOM by checking .may_split() before attempting to create a VMA copy. Signed-off-by: Dmitry Safonov --- mm/mremap.c | 11 ++++++++++- 1 file changed, 10 insertions(+), 1 deletion(-) diff --git a/mm/mremap.c b/mm/mremap.c index 898e9818ba6d..3c4047c23673 100644 --- a/mm/mremap.c +++ b/mm/mremap.c @@ -343,7 +343,7 @@ static unsigned long move_vma(struct vm_area_struct *= vma, unsigned long excess =3D 0; unsigned long hiwater_vm; int split =3D 0; - int err; + int err =3D 0; bool need_rmap_locks; =20 /* @@ -353,6 +353,15 @@ static unsigned long move_vma(struct vm_area_struct = *vma, if (mm->map_count >=3D sysctl_max_map_count - 3) return -ENOMEM; =20 + if (vma->vm_ops && vma->vm_ops->may_split) { + if (vma->vm_start !=3D old_addr) + err =3D vma->vm_ops->may_split(vma, old_addr); + if (!err && vma->vm_end !=3D old_addr + old_len) + err =3D vma->vm_ops->may_split(vma, old_addr + old_len); + if (err) + return err; + } + /* * Advise KSM to break any KSM pages in the area to be moved: * it would be confusing if they were to turn up at the new --=20 2.28.0