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 X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3CAB6C4740C for ; Mon, 9 Sep 2019 20:57:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 06B7C218AF for ; Mon, 9 Sep 2019 20:57:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727803AbfIIU51 (ORCPT ); Mon, 9 Sep 2019 16:57:27 -0400 Received: from www262.sakura.ne.jp ([202.181.97.72]:51977 "EHLO www262.sakura.ne.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726806AbfIIU51 (ORCPT ); Mon, 9 Sep 2019 16:57:27 -0400 Received: from fsav302.sakura.ne.jp (fsav302.sakura.ne.jp [153.120.85.133]) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTP id x89KvPPi038871; Tue, 10 Sep 2019 05:57:26 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Received: from www262.sakura.ne.jp (202.181.97.72) by fsav302.sakura.ne.jp (F-Secure/fsigk_smtp/530/fsav302.sakura.ne.jp); Tue, 10 Sep 2019 05:57:25 +0900 (JST) X-Virus-Status: clean(F-Secure/fsigk_smtp/530/fsav302.sakura.ne.jp) Received: from [192.168.1.8] (softbank126227201116.bbtec.net [126.227.201.116]) (authenticated bits=0) by www262.sakura.ne.jp (8.15.2/8.15.2) with ESMTPSA id x89KvPGd038866 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NO); Tue, 10 Sep 2019 05:57:25 +0900 (JST) (envelope-from penguin-kernel@I-love.SAKURA.ne.jp) Subject: Re: [PATCH] mm: avoid slub allocation while holding list_lock To: "Kirill A. Shutemov" , Yu Zhao Cc: Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org References: <20190909061016.173927-1-yuzhao@google.com> <20190909160052.cxpfdmnrqucsilz2@box> From: Tetsuo Handa Message-ID: Date: Tue, 10 Sep 2019 05:57:22 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20190909160052.cxpfdmnrqucsilz2@box> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/09/10 1:00, Kirill A. Shutemov wrote: > On Mon, Sep 09, 2019 at 12:10:16AM -0600, Yu Zhao wrote: >> If we are already under list_lock, don't call kmalloc(). Otherwise we >> will run into deadlock because kmalloc() also tries to grab the same >> lock. >> >> Instead, allocate pages directly. Given currently page->objects has >> 15 bits, we only need 1 page. We may waste some memory but we only do >> so when slub debug is on. >> >> WARNING: possible recursive locking detected >> -------------------------------------------- >> mount-encrypted/4921 is trying to acquire lock: >> (&(&n->list_lock)->rlock){-.-.}, at: ___slab_alloc+0x104/0x437 >> >> but task is already holding lock: >> (&(&n->list_lock)->rlock){-.-.}, at: __kmem_cache_shutdown+0x81/0x3cb >> >> other info that might help us debug this: >> Possible unsafe locking scenario: >> >> CPU0 >> ---- >> lock(&(&n->list_lock)->rlock); >> lock(&(&n->list_lock)->rlock); >> >> *** DEADLOCK *** >> >> Signed-off-by: Yu Zhao > > Looks sane to me: > > Acked-by: Kirill A. Shutemov > Really? Since page->objects is handled as bitmap, alignment should be BITS_PER_LONG than BITS_PER_BYTE (though in this particular case, get_order() would implicitly align BITS_PER_BYTE * PAGE_SIZE). But get_order(0) is an undefined behavior.