From patchwork Mon Oct 9 06:42:26 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 13412979 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 712ECE95A8D for ; Mon, 9 Oct 2023 06:42:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345315AbjJIGmk (ORCPT ); Mon, 9 Oct 2023 02:42:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35126 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345308AbjJIGmj (ORCPT ); Mon, 9 Oct 2023 02:42:39 -0400 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 D15BACA for ; Sun, 8 Oct 2023 23:42:37 -0700 (PDT) Received: by mail-yw1-x114a.google.com with SMTP id 00721157ae682-59f8040b2ffso66586907b3.3 for ; Sun, 08 Oct 2023 23:42:37 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1696833757; x=1697438557; 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=GMzA+bY5iQ55icqv7/c58xVjlf8IiONnVGODeN5A6AA=; b=bVDwtzWtwc1VM4vQGrACZvNw57uyX10S4ICovNdmKLlGBwAwXVt37DKrZ8fYdL+i6s hg/S5stmKoEql8LybZzVlqpG+Pz9UQvORdFX+wTv3OyhcHlW9NQOhkjkHl/iS0EDhb6H SZ0UO1RKmg//m24u1crbacIuBCwM3kvDIs2NR73ct6bSeVuTPW1YmQhujjjHuBBWRbXp ozrIQXnECsYK0I2maQFKV7syjcTk9GXMjfKYsNNe4Se2e9YdbXQ21H9zkxX7UpKjYAa/ JKzmQAjBHM13eetlwt1Dz5TWT7ccI94TsKSumlFFdfTLpWG6eQpJqd+QonllWgCYVoOB 7Jtg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1696833757; x=1697438557; 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=GMzA+bY5iQ55icqv7/c58xVjlf8IiONnVGODeN5A6AA=; b=hr4pdbPqhUKSRq10HfPjHySmLzgg6EhzsjTYPelDANdZWmxzjgKDu2wSt6ykrhB8xt FdEor/LEIGt69Yz81orF5p1dR2fHt8HJzDKZOKyAXs4p/p71fmpk8DSZPzQQFml7+Umr IrXMuNrpwTInZ1GDlejeNQsaxqfri2Q0Nljn/98YCdKDjFmQ4TGBRmwpx8CQ7ZR8OoE4 tg9ce5kdYj2xxVckeLHD2+nUpUYcNrAi6rU6KLe10IMbZ6HLztQSzsr3TynEvKM6faiG L7J+tq+m04nvbDZLknVzMBvtWecUqG4iu+XDr6zkckQO9Hcc3lrewLkXVONSATLlM+Ns cETQ== X-Gm-Message-State: AOJu0Yy9KXotgUZaSDxac1eKCQ21yziXnAsCpouk4BZJoQBwoVZdJu3m RMfQwI6inWyrirXIRjhi5/Cr1Sph+z4= X-Google-Smtp-Source: AGHT+IFtPbkNFD9Rxrba570q5f/tqYHiGOqoU9c9uHOquBYgh1LiUto5yoJwsPheCUdVazB3Qxt4pauoLww= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:201:3e83:601e:dc42:a455]) (user=surenb job=sendgmr) by 2002:a81:a809:0:b0:59b:ebe0:9fce with SMTP id f9-20020a81a809000000b0059bebe09fcemr261242ywh.5.1696833757037; Sun, 08 Oct 2023 23:42:37 -0700 (PDT) Date: Sun, 8 Oct 2023 23:42:26 -0700 In-Reply-To: <20231009064230.2952396-1-surenb@google.com> Mime-Version: 1.0 References: <20231009064230.2952396-1-surenb@google.com> X-Mailer: git-send-email 2.42.0.609.gbb76f46606-goog Message-ID: <20231009064230.2952396-2-surenb@google.com> Subject: [PATCH v3 1/3] 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, 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 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org 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 --- mm/rmap.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/mm/rmap.c b/mm/rmap.c index c1f11c9dbe61..f9ddc50269d2 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -542,7 +542,9 @@ 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(); +retry_under_rcu: anon_mapping = (unsigned long)READ_ONCE(folio->mapping); if ((anon_mapping & PAGE_MAPPING_FLAGS) != PAGE_MAPPING_ANON) goto out; @@ -552,6 +554,16 @@ 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); + goto retry_under_rcu; + } + /* * 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