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 C2054C433EF for ; Wed, 11 May 2022 19:50:25 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D0C296B0074; Wed, 11 May 2022 15:50:24 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CBA996B0075; Wed, 11 May 2022 15:50:24 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B83A96B0078; Wed, 11 May 2022 15:50:24 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id A64416B0074 for ; Wed, 11 May 2022 15:50:24 -0400 (EDT) Received: from smtpin08.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay13.hostedemail.com (Postfix) with ESMTP id 7CE186213D for ; Wed, 11 May 2022 19:50:24 +0000 (UTC) X-FDA: 79454503968.08.D1C774D Received: from mail-pl1-f176.google.com (mail-pl1-f176.google.com [209.85.214.176]) by imf10.hostedemail.com (Postfix) with ESMTP id 0763BC007C for ; Wed, 11 May 2022 19:50:00 +0000 (UTC) Received: by mail-pl1-f176.google.com with SMTP id j14so2890217plx.3 for ; Wed, 11 May 2022 12:50:23 -0700 (PDT) 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=NQqa4NCLuH69QVRWRKwlBaMthxo9RbegNopzdicXQlQ=; b=Iwsi1sTz6thBDZysbiByHudfOFMkxoIZcOUmMVXsDCHn56PUllgEgwJmqDNEpKFOKm aNlACEqSQCfMW7QLHqwu4iXZkG538AmcEzQHbQmv5N8131V3AbymGpLcPN/lQ3uc3E2s wOR43qzPZWZiomRsLkxDP8a62sIR+AGJHHO2RZxv4zZj3C17tEmrGBPmvzy3RC2erDF6 oX9Z5qRcBR2OEkBpl/ipw3akPfCWTegJUyN6JsvhV3BYzICcisuxcYg5mFvhHqcvVo+h 6/F7RE1Q5L4dNRKyjldl08Tu51ITqOPezd6mg3fzHfLfv+21V874RDfpDDS/7ePr7bbY L4uQ== X-Gm-Message-State: AOAM532309IdRKnR2sjeB95M+eX5FhbNfzVXMJKyKOiIWYFGz0eFrlHJ WdGhKBbq/XQHAbmgZqlDo1Q= X-Google-Smtp-Source: ABdhPJz0rPYrf6faYGgucXqaE8izHgU+jh+jnUWb+tXPQuELlzX4XQ2p5283OLQ3hg3fmxjaMZjGDg== X-Received: by 2002:a17:902:cec9:b0:15e:cbf4:c246 with SMTP id d9-20020a170902cec900b0015ecbf4c246mr27625166plg.1.1652298623146; Wed, 11 May 2022 12:50:23 -0700 (PDT) Received: from sultan-box.localdomain ([204.152.216.102]) by smtp.gmail.com with ESMTPSA id b8-20020a1709027e0800b0015ef27092aasm2292465plm.190.2022.05.11.12.50.21 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 11 May 2022 12:50:22 -0700 (PDT) Date: Wed, 11 May 2022 12:50:20 -0700 From: Sultan Alsawaf To: Minchan Kim Cc: stable@vger.kernel.org, Nitin Gupta , Sergey Senozhatsky , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] zsmalloc: Fix races between asynchronous zspage free and page migration Message-ID: References: <20220509024703.243847-1-sultan@kerneltoast.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: 3egzkq47pmdmpd7qwxhwyukgkmjiz8od X-Rspamd-Server: rspam07 X-Rspamd-Queue-Id: 0763BC007C X-Rspam-User: Authentication-Results: imf10.hostedemail.com; dkim=none; spf=pass (imf10.hostedemail.com: domain of sultan.kerneltoast@gmail.com designates 209.85.214.176 as permitted sender) smtp.mailfrom=sultan.kerneltoast@gmail.com; dmarc=none X-HE-Tag: 1652298600-687172 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 Wed, May 11, 2022 at 11:01:01AM -0700, Minchan Kim wrote: > On Sun, May 08, 2022 at 07:47:02PM -0700, Sultan Alsawaf wrote: > > Cc: stable@vger.kernel.org > > Fixes: 48b4800a1c6a ("zsmalloc: page migration support") > > Shouldn't the fix be Fixes: 77ff465799c6 ("zsmalloc: zs_page_migrate: skip > unnecessary loops but not return -EBUSY if zspage is not inuse)? > Because we didn't migrate ZS_EMPTY pages before. Hi, Yeah, 77ff465799c6 indeed seems like the commit that introduced the bug. > I couldn't get the point here. Why couldn't we simple lock zspage migration? > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c > index 9152fbde33b5..05ff2315b7b1 100644 > --- a/mm/zsmalloc.c > +++ b/mm/zsmalloc.c > @@ -1987,7 +1987,10 @@ static void async_free_zspage(struct work_struct *work) > > list_for_each_entry_safe(zspage, tmp, &free_pages, list) { > list_del(&zspage->list); > + > + migrate_read_lock(zspage); > lock_zspage(zspage); > + migrate_read_unlock(zspage); > > get_zspage_mapping(zspage, &class_idx, &fullness); > VM_BUG_ON(fullness != ZS_EMPTY); There are two problems with this: 1. migrate_read_lock() is a rwlock and lock_page() can sleep. 2. This will cause a deadlock because it violates the lock ordering in zs_page_migrate(), since zs_page_migrate() takes migrate_write_lock() under the page lock. Sultan