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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6B5C9C3DA78 for ; Tue, 17 Jan 2023 18:49:52 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 079816B0072; Tue, 17 Jan 2023 13:49:52 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 0026B6B0073; Tue, 17 Jan 2023 13:49:51 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DE5CC6B0074; Tue, 17 Jan 2023 13:49:51 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0014.hostedemail.com [216.40.44.14]) by kanga.kvack.org (Postfix) with ESMTP id D15C76B0072 for ; Tue, 17 Jan 2023 13:49:51 -0500 (EST) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay09.hostedemail.com (Postfix) with ESMTP id AF074801BF for ; Tue, 17 Jan 2023 18:49:51 +0000 (UTC) X-FDA: 80365180182.23.F51416C Received: from mail-yw1-f182.google.com (mail-yw1-f182.google.com [209.85.128.182]) by imf12.hostedemail.com (Postfix) with ESMTP id F0D214001C for ; Tue, 17 Jan 2023 18:49:49 +0000 (UTC) Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=p5fs5mLS; spf=pass (imf12.hostedemail.com: domain of surenb@google.com designates 209.85.128.182 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1673981390; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=iz0GQ7/w+mu6oDV5bKCsXpIO0gDrI/zJCZBxc6dizOg=; b=ueD2COYVg9Nw9kq0SAHKy/7Eb9oY45OcMkwxcuzP0+Y6lMlh3vnODtV5egmAjk2Jd4dKgD laf7n7+tqJnp04eARLVgwQY0hB4CvPxEW4rFq139hwzmsKoumfJePfVBHKA58A9+9d3iwQ bOX4xsEKrKhrVtRkKAYcV+x7FF2wHdg= ARC-Authentication-Results: i=1; imf12.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=p5fs5mLS; spf=pass (imf12.hostedemail.com: domain of surenb@google.com designates 209.85.128.182 as permitted sender) smtp.mailfrom=surenb@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1673981390; a=rsa-sha256; cv=none; b=0gi2ed5u8YGd+JftWl/azbcwWW/bRA5h3cDXvICBnt5nOvrPgTs5XDDFxkumNkuAA5zhNs inX/R3L0OZDPeA1bLE676JoUQB8usNN7AcHbi+olHLqRH9f0mcE+9LV4KXV/ECmMfh8BDN Hve4WV3KuPAkpzQw2RKusVTQdz3JRYc= Received: by mail-yw1-f182.google.com with SMTP id 00721157ae682-4d0f843c417so321883607b3.7 for ; Tue, 17 Jan 2023 10:49:49 -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=iz0GQ7/w+mu6oDV5bKCsXpIO0gDrI/zJCZBxc6dizOg=; b=p5fs5mLSVpER0JzqnFPms6ksIHjMhLnm0fGre8E+U/jXlE/W8pYmcWl5PGr886PDTB CCtdYmfgkYM4JMRjESQanIWyjIXlWHd/PxJFHITaVdlfn58FQ+NW2Zko5H4cXnDNBWke B565WEhHRxl6a6x1P63VIIsrRmgO45GgxGY3ttWlZkSOOq/tHi+ZkQ7B774p7YBhqesy u9cHULCi5YYM0ERasMFJ406wprrlp7om3hAtpCSPuwVEYfi6fMljV2/XAdpKw5OWsFJm yhC71JdRdTRRBJm9wugmwnlk8Z9bibkosJiO3CiDBD5UQ4mwnK82JkF8Too4UeebtXG7 Ckmg== 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=iz0GQ7/w+mu6oDV5bKCsXpIO0gDrI/zJCZBxc6dizOg=; b=fTXlSSVt17CGJD18j90a0w4Y15ZfvFNUxWWONxxaLh4VkAvK3WjRCdaQ1mng1UbQ/l PvKfDse8rz1C7seIRlV2JcXYwDLiAIG9SUwxewZvUSd9y6oDVi9zC3LOa0yEWGu35Grr hQKOB0tRuEd6Ga1ICP5DDqJuxLKOCWTHSIru5TH95Yri/tlEVUCc5Tqg8QBQpVsAaVTH l3xyKE29KC39TGc/ZsshllE4gp9Epth/AsLZtRzXwHp5Aj5X5Z0gJoFPbrxsjZflwBrW ZY0U7+DH5F0/mHZpgtarDp6/NLdq2g7Ag11HHPtoEkuidE1u4tdCzpR1TPABe2Rwa4oz UKcA== X-Gm-Message-State: AFqh2krhEbgow1937rp9wrxTUhAsnSjvZ+vauGj+iAmX1zibvozl8+XV lBa6bMfAgEpDcyqAhgrVuv4TOkD7gMYL1zRmSe0hgQ== X-Google-Smtp-Source: AMrXdXvI+MOkNBHOikckkXfQawDP5Ir9tQ5z55WvACj8+QlkWO3+VNjLWrjFnu2fznZ7jncOPRR0JlSu1xdrpp+UO5Y= X-Received: by 2002:a81:784c:0:b0:4e1:5013:6da1 with SMTP id t73-20020a81784c000000b004e150136da1mr617572ywc.218.1673981388803; Tue, 17 Jan 2023 10:49:48 -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 10:49:37 -0800 Message-ID: Subject: Re: [PATCH 41/41] mm: replace rw_semaphore with atomic_t in vma_lock To: Jann Horn Cc: Matthew Wilcox , 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, 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" X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: F0D214001C X-Rspam-User: X-Stat-Signature: ksbx4ybg8xiz8cr6qqytoy6bm95egga8 X-HE-Tag: 1673981389-102312 X-HE-Meta: U2FsdGVkX1+lv0NEmHjc+p8UemRvX1S0foE/caVf04E7fV888IR3x9yya+ey7RPyf1UdV2JSqs/ac3hSbEhEZE6SUHXMyDFm94jVjQpAOsxHgbYzMYA8IYkhF39Kno0F5xbD8214TLQnPKBGqy1ZEq8/xTBFw4ULwI/mZA4lDHqM07fKO0nD3kXUUsJ/yN825YpPmuNtIqtrvPyyiJ+i9NGKYb9kKUBUJNZxvzQiZk+Ki22qo/mvByoc1IujdTS1zJ4sOWhrLgxJCua81Z7H/evk3OEYNdUl+IHWBJT5qyg2WvcBy4kBxD7p5QJHuuI+281f7KLlKERq8xjPymhIslcizTI8+5rTWzzMwDqANSPn5lbMfpfefJYH/R+CsILT0x1qZbBLZb8nyCiY6wgc6qrJgyYTeQ20A5Rk7p9ieWvCzLExDURswYWXy3vGJNC98RkNgdmnCkMDw61Ae8fRLMbf+LWFQJdtvz3oEqMCF1mvWVxjF6pcysOJ3pttoOxhkk8XSd4fsQHak1AeF1VojqRR/ReaSvLcyHJPvD0s7YLcis8JL+9+5qCagPJIZzgkmyAgyrBgkA2FMhICwa+wVipn+s/lZ364sOZTcO5fy9Tff7buFnsQ4vrTTQeHNiGj0LO8HNDirSmN2M6VncBiDFlKQO9PjZMD+N6nEIycTjjj3M8yJOQmDNxR/Go+tzI0PhZHVybcEVOik24sOMUTfiGvxaQ6El6mX0+hJjjyir0G2yda7h1qtkl67GyBs5y3f10Kj7ial3FxuhosRUcvja2KAlElfBM9LHv65Nq/bquzuAp7rePKhy+W/BE1WOzTwFA5YO14vanApNcPf7JzKFlhvB00YPcmQpNwEFGdWckB6ocF0dUJNzYpV/g11v2V4D5JYceBU7+le6ZoYiWvWFzWG9SdRtiNH7jXHhMPUIC9i6/FPpM1W8YCv/1LpJrboegdKgER0k9nnzI5r3f i2DWJm4H Isjb2xsWFc4ArQs0mtPQ98++7sbJ9qm+RXI3ejMh8tofZNovVkCJQnb3TXA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jan 17, 2023 at 10:36 AM Jann Horn wrote: > > On Tue, Jan 17, 2023 at 7:31 PM Matthew Wilcox wrote: > > > > On Tue, Jan 17, 2023 at 10:26:32AM -0800, Suren Baghdasaryan wrote: > > > 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. > > > > Yes, but ... > > > > Task A: > > atomic_dec_and_test(&vma->vm_lock->count) > > Task B: > > munmap() > > write lock > > free VMA > > synchronize_rcu() > > VMA is really freed > > wake_up(&vma->vm_mm->vma_writer_wait); > > > > ... vma is freed. > > > > Now, I think this doesn't occur. I'm pretty sure that every caller of > > vma_read_unlock() is holding the RCU read lock. But maybe we should > > have that assertion? > > I don't see that. When do_user_addr_fault() is calling > vma_read_unlock(), there's no RCU read lock held, right? We free VMAs using call_rcu() after removing them from VMA tree. OTOH page fault handlers are searching for VMAs from inside RCU read section and calling vma_read_unlock() from there, see https://lore.kernel.org/all/20230109205336.3665937-29-surenb@google.com/. Once we take the VMA read-lock, it ensures that it can't be write-locked and if someone is destroying or isolating the VMA, it needs to write-lock it first.