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Mon, 14 Aug 2023 07:54:37 -0700 (PDT) MIME-Version: 1.0 References: <20230804152724.3090321-1-surenb@google.com> <20230804152724.3090321-6-surenb@google.com> In-Reply-To: <20230804152724.3090321-6-surenb@google.com> From: Jann Horn Date: Mon, 14 Aug 2023 16:54:01 +0200 Message-ID: Subject: Re: [PATCH v4 5/6] mm: always lock new vma before inserting into vma tree To: akpm@linux-foundation.org, Suren Baghdasaryan Cc: torvalds@linux-foundation.org, willy@infradead.org, liam.howlett@oracle.com, david@redhat.com, peterx@redhat.com, ldufour@linux.ibm.com, vbabka@suse.cz, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, hannes@cmpxchg.org, dave@stgolabs.net, hughd@google.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: 56BF2C0010 X-Stat-Signature: 57a5ucb6a19yys7sq94amcb9ohyi87oe X-Rspam-User: X-HE-Tag: 1692024878-7688 X-HE-Meta: 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 Frax2D9l 7RWCQXS9A7hqiEBIPRrj4te+MYkz87QNSrDRBQynHNBf8i57RL85NmQLFOZf87AUOjxgtHfldOpdzwobh+jJRHk/bI6n9iwUhHWPgPz8omfIgiwyezEBcy/0RTWbNHy0HByZtXa/KGwYTjQrBYss5ppXLqyJMCz7Nsz2ayuQBf0jNgRk/7p8ytMmfVoCrNCYQJvXKHGVEqjlelcwzWM1QRE0Uda73QYG0dy85gGJNU45fqDovo7oePloyOxxTFuys2BzipWgyjW3FVr9MfnB3nHJHOD/7txKFPhxqshugUK2sIL8obocHihevcdPV5Li7NCu6/ikYAxd3vp8= 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: @akpm can you fix this up? On Fri, Aug 4, 2023 at 5:27=E2=80=AFPM Suren Baghdasaryan wrote: > While it's not strictly necessary to lock a newly created vma before > adding it into the vma tree (as long as no further changes are performed > to it), it seems like a good policy to lock it and prevent accidental > changes after it becomes visible to the page faults. Lock the vma before > adding it into the vma tree. > > Suggested-by: Jann Horn > Signed-off-by: Suren Baghdasaryan > Reviewed-by: Liam R. Howlett > --- > mm/mmap.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 3937479d0e07..850a39dee075 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -412,6 +412,8 @@ static int vma_link(struct mm_struct *mm, struct vm_a= rea_struct *vma) > if (vma_iter_prealloc(&vmi)) > return -ENOMEM; > > + vma_start_write(vma); > + > if (vma->vm_file) { > mapping =3D vma->vm_file->f_mapping; > i_mmap_lock_write(mapping); Something went wrong when this part of the patch was applied, because of a conflict with "mm/mmap: move vma operations to mm_struct out of the critical section of file mapping lock"; see how this patch ended up in the mm tree: https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git/commit/?id=3D26= cb4dafc13871ab68a4fb480ca1e19381cff392 > @@ -403,6 +403,8 @@ static int vma_link(struct mm_struct *mm, struct vm_a= rea_struct *vma) > > vma_iter_store(&vmi, vma); > > + vma_start_write(vma); > + > if (vma->vm_file) { > mapping =3D vma->vm_file->f_mapping; > i_mmap_lock_write(mapping); The "vma_start_write()" has to be ordered before the "vma_iter_store(&vmi, vma)".