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 A2441C433F5 for ; Wed, 30 Mar 2022 05:02:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242690AbiC3FES (ORCPT ); Wed, 30 Mar 2022 01:04:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45710 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242686AbiC3FER (ORCPT ); Wed, 30 Mar 2022 01:04:17 -0400 Received: from mail-pl1-x62e.google.com (mail-pl1-x62e.google.com [IPv6:2607:f8b0:4864:20::62e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B2687CFB96 for ; Tue, 29 Mar 2022 22:02:32 -0700 (PDT) Received: by mail-pl1-x62e.google.com with SMTP id p17so19500305plo.9 for ; Tue, 29 Mar 2022 22:02:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=Q85yzQxuckTI85t4cJc6DzVDpQWWYMYpPgEAz27AZ68=; b=ZHB4+/xxhnaUd9srMjdIbuyk3a2PTfBvLvGAfiBjML6/F3kNlVnSuQW/XM+IzgUwbY 5/NhAggjA+JF2LrMbYNU0lxeZapTt/wS0JljVhTU2i2oWKUpxI0lxEbsL585kyDCCiUG wX4xh6bQKFgWZjJI2nBt95FnpSNviAw4BfWG0= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=Q85yzQxuckTI85t4cJc6DzVDpQWWYMYpPgEAz27AZ68=; b=ncncYsexfgnAMzA+UyV5IH8PwX1BuZ94bYm7tKojHWkE6+wwclt8mSWvXj+OvNzAr6 ljkmSsXcNbVzio71uUyK738R8yeh8eDEjji3EIQApp/7+EJrQ/++vI796jRTHQmcT7Tu 3j0rHV8aezlqhz757K1RA+WItLELlILmBDIkiguI+PWL/ohFqmBXsShm96wUy0QtZBF5 FPzhvDgjp+2O0rS7y7bbjx5a21bTGOZuBojE5+6arkKLDmzKtbgKdmYaCA3lIZpQT78q 462gUFFclpSukbFTMGmHdUgGxtzy28gIuNLNREaep8f+oNMVxX+quUThQHvTYdcP+s0i G9UQ== X-Gm-Message-State: AOAM533qEuktgdr0f1XTB+tzAd5qWAdQLqu0XQAcNTKDZsO4XBrRB5Lz 9EqjS7Tya+JmZvp2UH6mrpaUyA== X-Google-Smtp-Source: ABdhPJynLoJHDRoNgTS6HubmG1wyKYpNp3nof3cTY8dxxZLdxGtQyIunL3E09HMqA82pa808/H7T4Q== X-Received: by 2002:a17:902:d4cf:b0:154:2416:218e with SMTP id o15-20020a170902d4cf00b001542416218emr32897719plg.60.1648616552074; Tue, 29 Mar 2022 22:02:32 -0700 (PDT) Received: from google.com ([2401:fa00:8f:203:1719:a115:46dd:6b80]) by smtp.gmail.com with ESMTPSA id y8-20020a17090aa40800b001c6ccb2c395sm4524541pjp.9.2022.03.29.22.02.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Mar 2022 22:02:31 -0700 (PDT) Date: Wed, 30 Mar 2022 14:02:26 +0900 From: Sergey Senozhatsky To: Minchan Kim , Andrew Morton Cc: mm-commits@vger.kernel.org, stable@vger.kernel.org, senozhatsky@chromium.org, ngupta@vflare.org, ivan@cloudflare.com, david@redhat.com, axboe@kernel.dk, minchan@kernel.org Subject: Re: + mm-fix-unexpected-zeroed-page-mapping-with-zram-swap.patch added to -mm tree Message-ID: References: <20220326034321.2589FC340E8@smtp.kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220326034321.2589FC340E8@smtp.kernel.org> Precedence: bulk Reply-To: linux-kernel@vger.kernel.org List-ID: X-Mailing-List: mm-commits@vger.kernel.org On (22/03/25 20:43), Andrew Morton wrote: > Two processes under CLONE_VM cloning, user process can be corrupted by > seeing zeroed page unexpectedly. > > CPU A CPU B > > do_swap_page do_swap_page > SWP_SYNCHRONOUS_IO path SWP_SYNCHRONOUS_IO path > swap_readpage valid data > swap_slot_free_notify > delete zram entry > swap_readpage zeroed(invalid) data > pte_lock > map the *zero data* to userspace > pte_unlock > pte_lock > if (!pte_same) > goto out_nomap; > pte_unlock > return and next refault will > read zeroed data > > The swap_slot_free_notify is bogus for CLONE_VM case since it doesn't > increase the refcount of swap slot at copy_mm so it couldn't catch up > whether it's safe or not to discard data from backing device. In the > case, only the lock it could rely on to synchronize swap slot freeing is > page table lock. Thus, this patch gets rid of the swap_slot_free_notify > function. With this patch, CPU A will see correct data. > > CPU A CPU B > > do_swap_page do_swap_page > SWP_SYNCHRONOUS_IO path SWP_SYNCHRONOUS_IO path > swap_readpage original data > pte_lock > map the original data > swap_free > swap_range_free > bd_disk->fops->swap_slot_free_notify > swap_readpage read zeroed data > pte_unlock > pte_lock > if (!pte_same) > goto out_nomap; > pte_unlock > return > on next refault will see mapped data by CPU B > > The concern of the patch would increase memory consumption since it could > keep wasted memory with compressed form in zram as well as uncompressed > form in address space. However, most of cases of zram uses no readahead > and do_swap_page is followed by swap_free so it will free the compressed > form from in zram quickly. Minchan, a quick question, shouldn't this instead revert 3f2b1a04f4493?