From patchwork Wed Dec 6 10:36:55 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 750842 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="2Z8Ojc3+" Received: from mail-yw1-x114a.google.com (mail-yw1-x114a.google.com [IPv6:2607:f8b0:4864:20::114a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A70CB10CB for ; Wed, 6 Dec 2023 02:37:08 -0800 (PST) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-5d3a1e5f8d6so98446127b3.3 for ; Wed, 06 Dec 2023 02:37:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1701859028; x=1702463828; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=9XWOv5VjGfqn4Ye4rb6vL096BWUdHwApYaIgHelXwhw=; b=2Z8Ojc3+f1h+IDCp5TfrmeRF8GsigP5YQiSIY77l2jHvzg0Q/CSwgB8/u/W+SR0+SN AtBv7CX4I8zATdAILvO+i+uysAG2HJP9Kgxg1PgpxNm4g2NWOwKSX9S5i3ECOzCyB7KG Jpe9s3g8ZvsyrEhpE6jNB5PVMc/88Sa2/ItrmTsSEhdYsoh4EBaVyLFP3mpQgMridE5I on4mjyLL6IQlgpjQG0mG1dk5AdXC/BJr1Zr7snqx6RoDAm94qPB24kVBf/tySg4V+uew 8Hq7QA00cieb7ItkltuI2Jd918dEv8PWWzFgwAhnwR/Z8T0QLuj+x/t4weatrcLu+Usi f+bQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1701859028; x=1702463828; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=9XWOv5VjGfqn4Ye4rb6vL096BWUdHwApYaIgHelXwhw=; b=TyG6K8smFZNiRIYtlzfAy0DIbHbob7VC3N9gKMOoUYTREOpyPu6c6FnJfPDIKXK5nA 5l36hs0x5Bo0KKdttcT6I45fBzgRR6wgFEEAUzH8lYeBsjOg55zu+/5BtERg3tbakrfG JFYrPKrGCOLmZiY9+Bzzgs4joGU9sguAFJ9vPvyhu5j++qqGIZ46QDmXwD5H3UU690sa +JNEyjrWqlB8dunRFJoVDNuth+P1Rvsg9YP1PGAuh7nlnhk8m5TONJYIZwtknm2MPZCQ TokoqKNaS4Y6RKzifectY4tF+VPCK9N2ygTW5nvhsfCJUgnyAXidpQyuMyUBR6zuJZck 0Y9w== X-Gm-Message-State: AOJu0YwcfyO3qVPkw3TE9Z+NwEfJnxed3hp8vOOs21awgOiobevbGpPp kQXdZcLJQuuq30rdpsqSxdgG/zkANTg= X-Google-Smtp-Source: AGHT+IGCulkBJ+T0+9Lwp1vGAWeNFtPWyIYRPjeboNOQrA1z+wrU7Uo8XHJ4cQLDzSxZ9W28kHwF5PDUnGI= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:201:73f6:b5e2:415:6ba5]) (user=surenb job=sendgmr) by 2002:a25:7690:0:b0:db4:6936:48b7 with SMTP id r138-20020a257690000000b00db4693648b7mr5580ybc.2.1701859027736; Wed, 06 Dec 2023 02:37:07 -0800 (PST) Date: Wed, 6 Dec 2023 02:36:55 -0800 In-Reply-To: <20231206103702.3873743-1-surenb@google.com> Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20231206103702.3873743-1-surenb@google.com> X-Mailer: git-send-email 2.43.0.rc2.451.g8631bc7472-goog Message-ID: <20231206103702.3873743-2-surenb@google.com> Subject: [PATCH v6 1/5] mm/rmap: support move to different root anon_vma in folio_move_anon_rmap() From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: viro@zeniv.linux.org.uk, brauner@kernel.org, shuah@kernel.org, aarcange@redhat.com, lokeshgidra@google.com, peterx@redhat.com, david@redhat.com, ryan.roberts@arm.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, surenb@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 From: Andrea Arcangeli For now, folio_move_anon_rmap() was only used to move a folio to a different anon_vma after fork(), whereby the root anon_vma stayed unchanged. For that, it was sufficient to hold the folio lock when calling folio_move_anon_rmap(). However, we want to make use of folio_move_anon_rmap() to move folios between VMAs that have a different root anon_vma. As folio_referenced() performs an RMAP walk without holding the folio lock but only holding the anon_vma in read mode, holding the folio lock is insufficient. When moving to an anon_vma with a different root anon_vma, we'll have to hold both, the folio lock and the anon_vma lock in write mode. Consequently, whenever we succeeded in folio_lock_anon_vma_read() to read-lock the anon_vma, we have to re-check if the mapping was changed in the meantime. If that was the case, we have to retry. Note that folio_move_anon_rmap() must only be called if the anon page is exclusive to a process, and must not be called on KSM folios. This is a preparation for UFFDIO_MOVE, which will hold the folio lock, the anon_vma lock in write mode, and the mmap_lock in read mode. Signed-off-by: Andrea Arcangeli Signed-off-by: Suren Baghdasaryan Acked-by: Peter Xu --- mm/rmap.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/mm/rmap.c b/mm/rmap.c index 7a27a2b41802..525c5bc0b0b3 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; +retry: rcu_read_lock(); anon_mapping = (unsigned long)READ_ONCE(folio->mapping); if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON) @@ -552,6 +553,17 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio, anon_vma = (struct anon_vma *) (anon_mapping - PAGE_MAPPING_ANON); root_anon_vma = READ_ONCE(anon_vma->root); if (down_read_trylock(&root_anon_vma->rwsem)) { + /* + * folio_move_anon_rmap() might have changed the anon_vma as we + * might not hold the folio lock here. + */ + if (unlikely((unsigned long)READ_ONCE(folio->mapping) != + anon_mapping)) { + up_read(&root_anon_vma->rwsem); + rcu_read_unlock(); + goto retry; + } + /* * If the folio is still mapped, then this anon_vma is still * its anon_vma, and holding the mutex ensures that it will @@ -586,6 +598,18 @@ struct anon_vma *folio_lock_anon_vma_read(struct folio *folio, rcu_read_unlock(); anon_vma_lock_read(anon_vma); + /* + * folio_move_anon_rmap() might have changed the anon_vma as we might + * not hold the folio lock here. + */ + 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 retry; + } + if (atomic_dec_and_test(&anon_vma->refcount)) { /* * Oops, we held the last refcount, release the lock