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Howlett" Cc: Suren Baghdasaryan , Andrii Nakryiko , Vlastimil Babka , sidhartha.kumar@oracle.com, Matthew Wilcox , linux-fsdevel@vger.kernel.org, bpf@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 1/5] mm/mmap: Correctly position vma_iterator in __split_vma() Message-ID: <119b01ac-a57a-43cf-90ca-093e850c4b7e@lucifer.local> References: <20240531163217.1584450-1-Liam.Howlett@oracle.com> <20240531163217.1584450-2-Liam.Howlett@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240531163217.1584450-2-Liam.Howlett@oracle.com> X-Rspamd-Queue-Id: 443DD20015 X-Stat-Signature: i4d8oeybwgu4kmu4nmcg64zp874cac4m X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1718021345-20960 X-HE-Meta: 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 CG1KxNVZ 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.066559, 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 Fri, May 31, 2024 at 12:32:13PM -0400, Liam R. Howlett wrote: > The vma iterator may be left pointing to the newly created vma. This > happens when inserting the new vma at the end of the old vma > (!new_below). > > The incorrect position in the vma iterator is not exposed currently > since the vma iterator is repositioned in the munmap path and is not > reused in any of the other paths. > > This has limited impact in the current code, but is required for future > changes. > > Fixes: b2b3b886738f ("mm: don't use __vma_adjust() in __split_vma()") > Signed-off-by: Liam R. Howlett > --- > mm/mmap.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 83b4682ec85c..31d464e6a656 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -2442,6 +2442,9 @@ static int __split_vma(struct vma_iterator *vmi, struct vm_area_struct *vma, > /* Success. */ > if (new_below) > vma_next(vmi); > + else > + vma_prev(vmi); > + > return 0; > > out_free_mpol: > -- > 2.43.0 > Looks good to me. As Suren alludes to, I agree that it's important to comment to indicate that you want to move the iterator to point to the VMA that's been shrunk rather than the newly inserted VMA. Reviewed-by: Lorenzo Stoakes