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[70.31.27.79]) by smtp.gmail.com with ESMTPSA id bq38-20020a05620a46a600b006fc40dafaa2sm20433574qkb.8.2022.12.08.13.05.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 08 Dec 2022 13:05:47 -0800 (PST) Date: Thu, 8 Dec 2022 16:05:46 -0500 From: Peter Xu To: David Hildenbrand Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Jann Horn , Andrea Arcangeli , James Houghton , Rik van Riel , Miaohe Lin , Nadav Amit , John Hubbard , Mike Kravetz , Andrew Morton , Muchun Song Subject: Re: [PATCH v2 10/10] mm/hugetlb: Document why page_vma_mapped_walk() is safe to walk Message-ID: References: <20221207203034.650899-1-peterx@redhat.com> <20221207203158.651092-1-peterx@redhat.com> <799d6831-2af3-72c1-84b2-1f0454a46c07@redhat.com> MIME-Version: 1.0 In-Reply-To: <799d6831-2af3-72c1-84b2-1f0454a46c07@redhat.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: B580640006 X-Stat-Signature: u5z6rdubhq6gei66zrs4bpc9yo1puz4r X-HE-Tag: 1670533556-736341 X-HE-Meta: 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 UVG+MSPr oMEm+KZoxHVCQHaRLfG/JClplZVuFO++5C81fHfq4GfIZd8+OAtOL2ru02A/9dPyXb+n7nwkXJXbhgetkQcJIZFS5mnAUlVYkgFrcU3JZBTVEPWOXT67MYHbJJ8UETO4g3HDUX/dKLxDeVLYUaMXkiQ+iJIO+iH2rUrTHI+p4nvmTdStZOnWhHc3+Txne1Negb9hRyAMO8RVJeYXTsFkKT9IRgyvkwRJjbFUW 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 Thu, Dec 08, 2022 at 02:16:03PM +0100, David Hildenbrand wrote: > On 07.12.22 21:31, Peter Xu wrote: > > Taking vma lock here is not needed for now because all potential hugetlb > > walkers here should have i_mmap_rwsem held. Document the fact. > > > > Reviewed-by: Mike Kravetz > > Signed-off-by: Peter Xu > > --- > > mm/page_vma_mapped.c | 10 ++++++++-- > > 1 file changed, 8 insertions(+), 2 deletions(-) > > > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > > index e97b2e23bd28..2e59a0419d22 100644 > > --- a/mm/page_vma_mapped.c > > +++ b/mm/page_vma_mapped.c > > @@ -168,8 +168,14 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > > /* The only possible mapping was handled on last iteration */ > > if (pvmw->pte) > > return not_found(pvmw); > > - > > - /* when pud is not present, pte will be NULL */ > > + /* > > + * NOTE: we don't need explicit lock here to walk the > > + * hugetlb pgtable because either (1) potential callers of > > + * hugetlb pvmw currently holds i_mmap_rwsem, or (2) the > > + * caller will not walk a hugetlb vma (e.g. ksm or uprobe). > > + * When one day this rule breaks, one will get a warning > > + * in hugetlb_walk(), and then we'll figure out what to do. > > + */ > > pvmw->pte = hugetlb_walk(vma, pvmw->address, size); > > if (!pvmw->pte) > > return false; > > Would it make sense to squash that into the previous commit? Sure thing. -- Peter Xu