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 E5809C678D4 for ; Tue, 17 Jan 2023 19:22:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235342AbjAQTVv (ORCPT ); Tue, 17 Jan 2023 14:21:51 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45746 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232731AbjAQTMp (ORCPT ); Tue, 17 Jan 2023 14:12:45 -0500 Received: from mail-yb1-xb33.google.com (mail-yb1-xb33.google.com [IPv6:2607:f8b0:4864:20::b33]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3D59637B7E for ; Tue, 17 Jan 2023 10:26:44 -0800 (PST) Received: by mail-yb1-xb33.google.com with SMTP id v19so29278839ybv.1 for ; Tue, 17 Jan 2023 10:26:44 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=4j3tl0DYASqrjkqUxwz46bG4ROPSgLPddwJUIyGPfX8=; b=hBh7iHpA0qfvzb6NYfBFfodVZoJZG89lkfXRit37mYAmeC5nBFxn8EQS0LUAe3jcVo C5FRsaxj+EKLI2jWmHfjp8neugrXB9pI/nKBzQoYA1YpgFoWtnyOa5v24hYecpIUquUN KSNNz94C5dAuBzIbNy+BM3HlLgWGdJfq88KPVCdqr5XOURSiVIt8NC83fhsqzZZfL4An QFEI0BAISvqo9iX+zoQ1BM4zTAWiTj/t7PqnS+AcCO7l4eOGIMMkEF+giJ7BJLV4QoxO D/AunpSl6jrX3m5nr8I4wWYNarHbEt/jf3IwcNd/YSKXxcntJzTg/UwFDPfUl4301hBU s7qQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=4j3tl0DYASqrjkqUxwz46bG4ROPSgLPddwJUIyGPfX8=; b=0kmhzCyV4vOJvL8Igcw4u3VgQOB9EGGbsl+HHZ2dBLZ+NNZE81qxnOlS1AaK9Dwg65 IEiR9Lf9ei9uCQhuotdLJ9Dg5HNc8VPni0qqRwqcFDI646Ckfjz0wXdvoBpUDBCRo4Tp AdMSK0vrWo/F4rBtePNyFBTdvWbbvpkdOhl3zHj5/UU7iumrZD1e80usi4t8IVcPTUVU iuP++V0oYu7ervp7fd+DkbwT/hukap/lOtLj6ALKGOTIucfhgAcsdPG4JU8myrC+ygMU BfEIld18ItAXzFuROyrVVczvE9GiI8jpbg4HY09KsD98w+Uu9mI6k7KYl17Ie2edPu8o KAAA== X-Gm-Message-State: AFqh2kp1hgn2FD98/cb30hsjybIYCX9iITYiVQhZDzi2yYt/D5AFO45I qQ4l3PHEs9UgOF4Ciy8Xlhb5e+YnD8KcigvLc5vrpA== X-Google-Smtp-Source: AMrXdXs7BogT7SdoZ360ei40N37ZNOM5XxWUzxAMlDXlaXiTGADLynxjLDtiuGW4hqoQrK26rMYv0lMAFrNqu+/4diM= X-Received: by 2002:a25:ceca:0:b0:7e4:115c:9cf6 with SMTP id x193-20020a25ceca000000b007e4115c9cf6mr537549ybe.316.1673980003301; Tue, 17 Jan 2023 10:26:43 -0800 (PST) MIME-Version: 1.0 References: <20230109205336.3665937-1-surenb@google.com> <20230109205336.3665937-42-surenb@google.com> In-Reply-To: From: Suren Baghdasaryan Date: Tue, 17 Jan 2023 10:26:32 -0800 Message-ID: Subject: Re: [PATCH 41/41] mm: replace rw_semaphore with atomic_t in vma_lock To: Jann Horn Cc: akpm@linux-foundation.org, michel@lespinasse.org, jglisse@google.com, mhocko@suse.com, vbabka@suse.cz, hannes@cmpxchg.org, mgorman@techsingularity.net, dave@stgolabs.net, willy@infradead.org, liam.howlett@oracle.com, peterz@infradead.org, ldufour@linux.ibm.com, laurent.dufour@fr.ibm.com, paulmck@kernel.org, luto@kernel.org, songliubraving@fb.com, peterx@redhat.com, david@redhat.com, dhowells@redhat.com, hughd@google.com, bigeasy@linutronix.de, kent.overstreet@linux.dev, punit.agrawal@bytedance.com, lstoakes@gmail.com, peterjung1337@gmail.com, rientjes@google.com, axelrasmussen@google.com, joelaf@google.com, minchan@google.com, shakeelb@google.com, tatashin@google.com, edumazet@google.com, gthelen@google.com, gurua@google.com, arjunroy@google.com, soheil@google.com, hughlynch@google.com, leewalsh@google.com, posk@google.com, linux-mm@kvack.org, linux-arm-kernel@lists.infradead.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@android.com Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jan 17, 2023 at 10:12 AM Jann Horn wrote: > > On Mon, Jan 9, 2023 at 9:55 PM Suren Baghdasaryan wrote: > > rw_semaphore is a sizable structure of 40 bytes and consumes > > considerable space for each vm_area_struct. However vma_lock has > > two important specifics which can be used to replace rw_semaphore > > with a simpler structure: > [...] > > static inline void vma_read_unlock(struct vm_area_struct *vma) > > { > > - up_read(&vma->vm_lock->lock); > > + if (atomic_dec_and_test(&vma->vm_lock->count)) > > + wake_up(&vma->vm_mm->vma_writer_wait); > > } > > I haven't properly reviewed this, but this bit looks like a > use-after-free because you're accessing the vma after dropping your > reference on it. You'd have to first look up the vma->vm_mm, then do > the atomic_dec_and_test(), and afterwards do the wake_up() without > touching the vma. Or alternatively wrap the whole thing in an RCU > read-side critical section if the VMA is freed with RCU delay. vm_lock->count does not control the lifetime of the VMA, it's a counter of how many readers took the lock or it's negative if the lock is write-locked.