From patchwork Sat Oct 28 00:38:11 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Suren Baghdasaryan X-Patchwork-Id: 739147 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 37A56C27C4A for ; Sat, 28 Oct 2023 00:38:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232877AbjJ1Ai3 (ORCPT ); Fri, 27 Oct 2023 20:38:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231481AbjJ1Ai2 (ORCPT ); Fri, 27 Oct 2023 20:38:28 -0400 Received: from mail-yw1-x1149.google.com (mail-yw1-x1149.google.com [IPv6:2607:f8b0:4864:20::1149]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B8C431BD for ; Fri, 27 Oct 2023 17:38:25 -0700 (PDT) Received: by mail-yw1-x1149.google.com with SMTP id 00721157ae682-5a7b9e83b70so24976797b3.0 for ; Fri, 27 Oct 2023 17:38:25 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1698453505; x=1699058305; 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=Hd9WkLbC3/9tKbDr398vMG9sjKzgB6769/dIszrNtnA=; b=0WMvlORCh5eNdKteXyjztoAPal+jeVc94WtxFTyTPkacbGB6Uy7qO0oopPVCMS9Kd1 R6uAt5fpwgyCJTj6v7zu5LWroSrxw7hWH7F/AskFMri4nDXpZkTWBMaZW5AVkZQ0Eb9T jaDFBOuWJSii9w/2Cm/unGNPKIB8qRnOenqt+O5DWva8wHHvYiCmxo9awZtx1LPi3Apq LPrhLrbJ/r3UdBs9s+lelrfO58TjmSAnP3SWoou9mSBNB5lEebCs5TllNteyXojSprgu a6rNx+UM8kpYJMO1nM1Ty7iSYJGeNOx5rsG217WxbZEvhhW1P2LLKscvERjDHj3XKy3G /+Aw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1698453505; x=1699058305; 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=Hd9WkLbC3/9tKbDr398vMG9sjKzgB6769/dIszrNtnA=; b=OEY7W3whWaFHhVue5wLfeavBx58v1Xl2Rh1gbpbv6uoyPWo4atiWynqtpoxkjRYbf8 +P2YxvtXwf1a75YCp+afj62PP8lQZp3MtAV897rjod9yupKl3suTmUq4ah18LhWpxE8e ys1/lSNKbpSzT3Vx3fI5Di7xJlrHdi6voSBNL0uxgLKSUDhUsSCt/WqOUqUNm4xa+kPw 7V2/WtxFWH29lpcs6RUh+ZBuXOQpFd0/5Xt+EKdS6AetRf71XIqZMEW6YX1Q/2A8XLPW 9fzh7F8f0cNsx7Pq0y47mS7zEUSKCoWX2FhCtvBTt36mmhfJlxkopJ/IhOiNCJYSSqMe YUMA== X-Gm-Message-State: AOJu0YzP8YTbYycRho+qCPRSUWNTgLK4OEdIR0U6WFCJIGbr4iQYYyRZ 0iPuWbgmCkmhvX6GZ2nhvbmWyLJB0go= X-Google-Smtp-Source: AGHT+IEhFUjmYdEXljORLOc7MoR1TUT63j0H8MtfIU3FFKJvRVJyyGkKkhRak6IgKRfrZGiSU7tVlIjlryE= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:201:cba3:7e7f:79e4:fa57]) (user=surenb job=sendgmr) by 2002:a81:7648:0:b0:59b:b0b1:d75a with SMTP id j8-20020a817648000000b0059bb0b1d75amr194570ywk.4.1698453504908; Fri, 27 Oct 2023 17:38:24 -0700 (PDT) Date: Fri, 27 Oct 2023 17:38:11 -0700 In-Reply-To: <20231028003819.652322-1-surenb@google.com> Mime-Version: 1.0 References: <20231028003819.652322-1-surenb@google.com> X-Mailer: git-send-email 2.42.0.820.g83a721a137-goog Message-ID: <20231028003819.652322-2-surenb@google.com> Subject: [PATCH v4 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, 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-kselftest@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 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