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Thu, 28 Sep 2023 13:03:53 -0700 (PDT) MIME-Version: 1.0 References: <20230923013148.1390521-1-surenb@google.com> <20230923013148.1390521-2-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Thu, 28 Sep 2023 13:03:42 -0700 Message-ID: Subject: Re: [PATCH v2 1/3] userfaultfd: UFFDIO_REMAP: rmap preparation To: Peter Xu Cc: akpm@linux-foundation.org, viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, david@redhat.com, hughd@google.com, mhocko@suse.com, axelrasmussen@google.com, rppt@kernel.org, willy@infradead.org, Liam.Howlett@oracle.com, jannh@google.com, zhangpeng362@huawei.com, bgeffon@google.com, kaleshsingh@google.com, ngeoffray@google.com, jdduke@google.com, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 4CCF9C0002 X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: p1oujxidy71htkxoo965znp8qgs4gdyb X-HE-Tag: 1695931434-813992 X-HE-Meta: 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 HOD6es7i nJY31mHPg4dyMwUttH4IGhU8EbQZNS3hue/87wV5IL+kUCcAtd50hnoWTvx7L1MwNOCqDZHDr8A+aLMEveCJI/9g8xdirqIhtHYs9HP2doCzofmjbxq6dsCa5bST0OyMs3LfTV98CrqwEVBR9MM1FcTNTVJTlEoBed2M6WPn7RMk2FpuJwa62gfo+uBYT3kNR8AuCNQUqjN5OpPMD9AtPOU0QAaJaFAGOekTNcPG6+4AUXmNxSXfV9yDqLBu2MXsYr+sfadhkfin6NOdQjpnmR5QSEdbFHa5k1Is45/yQFezAIso= 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, Sep 28, 2023 at 9:23=E2=80=AFAM Peter Xu wrote: > > Suren, > > Sorry to review so late. > > On Fri, Sep 22, 2023 at 06:31:44PM -0700, Suren Baghdasaryan wrote: > > diff --git a/mm/rmap.c b/mm/rmap.c > > index ec7f8e6c9e48..c1ebbd23fa61 100644 > > --- a/mm/rmap.c > > +++ b/mm/rmap.c > > @@ -542,6 +542,7 @@ struct anon_vma *folio_lock_anon_vma_read(struct fo= lio *folio, > > struct anon_vma *root_anon_vma; > > unsigned long anon_mapping; > > > > +repeat: > > rcu_read_lock(); > > anon_mapping =3D (unsigned long)READ_ONCE(folio->mapping); > > if ((anon_mapping & PAGE_MAPPING_FLAGS) !=3D PAGE_MAPPING_ANON) > > @@ -586,6 +587,18 @@ struct anon_vma *folio_lock_anon_vma_read(struct f= olio *folio, > > rcu_read_unlock(); > > anon_vma_lock_read(anon_vma); > > > > + /* > > + * Check if UFFDIO_REMAP changed the anon_vma. This is needed > > + * because we don't assume the folio was locked. > > + */ > > + if (unlikely((unsigned long) READ_ONCE(folio->mapping) !=3D > > + anon_mapping)) { > > + anon_vma_unlock_read(anon_vma); > > + put_anon_vma(anon_vma); > > + anon_vma =3D NULL; > > + goto repeat; > > + } > > We have an open-coded fast path above this: > > if (down_read_trylock(&root_anon_vma->rwsem)) { > /* > * If the folio is still mapped, then this anon_vma is st= ill > * its anon_vma, and holding the mutex ensures that it wi= ll > * not go away, see anon_vma_free(). > */ > if (!folio_mapped(folio)) { > up_read(&root_anon_vma->rwsem); > anon_vma =3D NULL; > } > goto out; > } > > Would that also need such check? Yes, I think they should be handled the same way. Will fix. Thanks! > > > + > > if (atomic_dec_and_test(&anon_vma->refcount)) { > > /* > > * Oops, we held the last refcount, release the lock > > -- > > 2.42.0.515.g380fc7ccd1-goog > > > > -- > Peter Xu >