From mboxrd@z Thu Jan 1 00:00:00 1970 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 C7D8DC433EF for ; Tue, 22 Feb 2022 05:40:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229853AbiBVFlF (ORCPT ); Tue, 22 Feb 2022 00:41:05 -0500 Received: from gmail-smtp-in.l.google.com ([23.128.96.19]:32994 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229775AbiBVFk5 (ORCPT ); Tue, 22 Feb 2022 00:40:57 -0500 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 372859D075 for ; Mon, 21 Feb 2022 21:40:33 -0800 (PST) Received: by mail-yb1-xb49.google.com with SMTP id s11-20020a255e0b000000b0062277953037so22966440ybb.21 for ; Mon, 21 Feb 2022 21:40:33 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:in-reply-to:message-id:mime-version:references:subject:from:to :cc; bh=EUVVGZ+sfFkAlbWcLcOfWelo8aSG6wtK/MR4mUfnNyc=; b=fpKWCGjam3h+oTc0b3WTir63RzOkNxXZgU5vtYBVjVlxzP5vP/UzSd57jCvC6qB9QY wnW7RUHe1MmvyANTL3zgrIrab9nIWp9DhoBpbeeL8c1uF0/9Oh6Q2wRSBgXSpcue+JVq rUzEGcNR0RVhA+BN4ZOd2DlPj1XYJBw4WnotnP3QgboCwWf3osqEqMWixUmN//eQx9jr O2rDmJeaQcpGM0+aP2JGf5YVs1XKpozN2vXj1EKQ/icvgRL1sGoWkuX8qm/EsMHDe0pj U9PuDoDRtQLLQGx/aXAe/1kKHlALYnkO3Qt2O/eQnn0ydTcdIUKdkDsP39r5Qg7MuYY/ CNbw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:in-reply-to:message-id:mime-version :references:subject:from:to:cc; bh=EUVVGZ+sfFkAlbWcLcOfWelo8aSG6wtK/MR4mUfnNyc=; b=UviYBqe2ua0dn8JQD+V2VcJBsvlD0AIg6IbAqyiYR8/q65GObkLkuvxybPYdGPBZh4 O+z117g+iQRqIIEXVXroZ4YUI5UlaU3Csl60Uh3Wh4Wlxku5GabZPfSNJvlk73ikJUTw GHP1SE4Fl8v5382LVehcIw8h9IU+VrIfu70z8jXOR6Fa5k1ZcUyZ8I0oEQdnpqAFB7rN LKCIytXaQEZCDTEBu+ro+cZtpwSG+9BERHgzYniIWn8yJMxdDo0+PU5z5Tl5Kl0L88bf HP2JS/TVMTHQBjT6/aoAqO1kP3Rczasbdcs7ULyiM/TBNtY8n3hNw88nXWxsS0xQQZiX x7Fg== X-Gm-Message-State: AOAM531Iwfc4i2Jtlb7tPfI/b2WUBMf7JemrW2E9TpPN/X7s54nDgMoX vwmLY1NZQV2AtrINeESxf0HdNZURnR8= X-Google-Smtp-Source: ABdhPJwVOasBVfLeQeogd5ubt0z+Z2Jo+Med/RLmizMF6Vlq5T8zcqx5UBl7TcdJuZhVwz7vc9q5T1juSek= X-Received: from surenb-desktop.mtv.corp.google.com ([2620:15c:211:200:79c1:8a4c:5d17:670f]) (user=surenb job=sendgmr) by 2002:a81:6184:0:b0:2d6:c22c:2a66 with SMTP id v126-20020a816184000000b002d6c22c2a66mr16578937ywb.311.1645508432422; Mon, 21 Feb 2022 21:40:32 -0800 (PST) Date: Mon, 21 Feb 2022 21:40:24 -0800 In-Reply-To: <20220222054025.3412898-1-surenb@google.com> Message-Id: <20220222054025.3412898-2-surenb@google.com> Mime-Version: 1.0 References: <20220222054025.3412898-1-surenb@google.com> X-Mailer: git-send-email 2.35.1.473.g83b2b277ed-goog Subject: [PATCH 2/3] mm: prevent vm_area_struct::anon_name refcount saturation From: Suren Baghdasaryan To: akpm@linux-foundation.org Cc: ccross@google.com, sumit.semwal@linaro.org, mhocko@suse.com, dave.hansen@intel.com, keescook@chromium.org, willy@infradead.org, kirill.shutemov@linux.intel.com, vbabka@suse.cz, hannes@cmpxchg.org, ebiederm@xmission.com, brauner@kernel.org, legion@kernel.org, ran.xiaokai@zte.com.cn, sashal@kernel.org, chris.hyser@oracle.com, dave@stgolabs.net, pcc@google.com, caoxiaofeng@yulong.com, david@redhat.com, gorcunov@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@android.com, surenb@google.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org A deep process chain with many vmas could grow really high. kref refcounting interface used in anon_vma_name structure will detect a counter overflow when it reaches REFCOUNT_SATURATED value but will only generate a warning about broken refcounting. To ensure anon_vma_name refcount does not overflow, stop anon_vma_name sharing when the refcount reaches INT_MAX, which still leaves INT_MAX/2 values before the counter reaches REFCOUNT_SATURATED. This should provide enough headroom for raising the refcounts temporarily. Suggested-by: Michal Hocko Signed-off-by: Suren Baghdasaryan --- include/linux/mm_inline.h | 18 ++++++++++++++---- mm/madvise.c | 3 +-- 2 files changed, 15 insertions(+), 6 deletions(-) diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h index 70b619442d56..b189e2638843 100644 --- a/include/linux/mm_inline.h +++ b/include/linux/mm_inline.h @@ -156,15 +156,25 @@ static inline void anon_vma_name_get(struct anon_vma_name *anon_name) extern void anon_vma_name_put(struct anon_vma_name *anon_name); +static inline +struct anon_vma_name *anon_vma_name_reuse(struct anon_vma_name *anon_name) +{ + /* Prevent anon_name refcount saturation early on */ + if (kref_read(&anon_name->kref) < INT_MAX) { + anon_vma_name_get(anon_name); + return anon_name; + + } + return anon_vma_name_alloc(anon_name->name); +} + static inline void dup_vma_anon_name(struct vm_area_struct *orig_vma, struct vm_area_struct *new_vma) { struct anon_vma_name *anon_name = vma_anon_name(orig_vma); - if (anon_name) { - anon_vma_name_get(anon_name); - new_vma->anon_name = anon_name; - } + if (anon_name) + new_vma->anon_name = anon_vma_name_reuse(anon_name); } static inline void free_vma_anon_name(struct vm_area_struct *vma) diff --git a/mm/madvise.c b/mm/madvise.c index f81d62d8ce9b..a395884aeecb 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -122,8 +122,7 @@ static int replace_vma_anon_name(struct vm_area_struct *vma, if (anon_vma_name_eq(orig_name, anon_name)) return 0; - anon_vma_name_get(anon_name); - vma->anon_name = anon_name; + vma->anon_name = anon_vma_name_reuse(anon_name); anon_vma_name_put(orig_name); return 0; -- 2.35.1.473.g83b2b277ed-goog