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[99.254.144.39]) by smtp.gmail.com with ESMTPSA id l11-20020ac84ccb000000b004181441cb2dsm3585433qtv.34.2023.09.28.09.23.30 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Sep 2023 09:23:32 -0700 (PDT) Date: Thu, 28 Sep 2023 12:23:28 -0400 From: Peter Xu To: Suren Baghdasaryan 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 Subject: Re: [PATCH v2 1/3] userfaultfd: UFFDIO_REMAP: rmap preparation Message-ID: References: <20230923013148.1390521-1-surenb@google.com> <20230923013148.1390521-2-surenb@google.com> MIME-Version: 1.0 In-Reply-To: <20230923013148.1390521-2-surenb@google.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: 25281160013 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 35r7azhtwbxuq6ysjpah1mzyhpd35pgo X-HE-Tag: 1695918226-691785 X-HE-Meta: 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 BtMTHge0 1NnU4Ym0F4CqmwIVWBf28NgZteGPls52siZx7900/FjaOpCKhan+57i63CNkNnXXC4qvPadeCM+iaCJZYfJLULtlLYO4r5O4WHsjTi+tgJmiwynkfdUA56rMAbsqC0577cEk+2qArIdsbHWlGBBqBdJw2OcYwFladg5tjmZXTTXfGyLzOv44DXNJoSXhd+TO56NJBVbQVeqq4WyFR4yJ7Csl1XU7y6kz2BARFmMgCwMsOkaBRVhs3MMWMF8/CDLPYvsv0y90Bq2jycv9MO/2twjo+a3t+0hmZLrVtwtP3Kp0JZGWVkhANujmnIFq2rGzXsU3ZA8BffMmdXWva+ZBOGuuhHMqfkI0LmF4ztfePBsZ1QYTrcdxBXVPShbHZ/5klcZVWlKq7oyW0UyVJcffkhHb2PPUJRkuHdzAD 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: 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 folio *folio, > struct anon_vma *root_anon_vma; > unsigned long anon_mapping; > > +repeat: > rcu_read_lock(); > anon_mapping = (unsigned long)READ_ONCE(folio->mapping); > if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON) > @@ -586,6 +587,18 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *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) != > + anon_mapping)) { > + anon_vma_unlock_read(anon_vma); > + put_anon_vma(anon_vma); > + anon_vma = 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 still * its anon_vma, and holding the mutex ensures that it will * not go away, see anon_vma_free(). */ if (!folio_mapped(folio)) { up_read(&root_anon_vma->rwsem); anon_vma = NULL; } goto out; } Would that also need such check? > + > 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