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=-5.3 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 17783C43331 for ; Sat, 9 Nov 2019 20:52:32 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id B066021848 for ; Sat, 9 Nov 2019 20:52:31 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B066021848 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 210B06B0003; Sat, 9 Nov 2019 15:52:31 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 1C05A6B0006; Sat, 9 Nov 2019 15:52:31 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 0FE836B0007; Sat, 9 Nov 2019 15:52:31 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0030.hostedemail.com [216.40.44.30]) by kanga.kvack.org (Postfix) with ESMTP id F01BD6B0003 for ; Sat, 9 Nov 2019 15:52:30 -0500 (EST) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id B00AA181AEF15 for ; Sat, 9 Nov 2019 20:52:30 +0000 (UTC) X-FDA: 76137937260.16.burst09_6d354e263aa2f X-HE-Tag: burst09_6d354e263aa2f X-Filterd-Recvd-Size: 4184 Received: from gentwo.org (gentwo.org [3.19.106.255]) by imf28.hostedemail.com (Postfix) with ESMTP for ; Sat, 9 Nov 2019 20:52:30 +0000 (UTC) Received: by gentwo.org (Postfix, from userid 1002) id 9CEE23EC14; Sat, 9 Nov 2019 20:52:29 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by gentwo.org (Postfix) with ESMTP id 9A0DA3E886; Sat, 9 Nov 2019 20:52:29 +0000 (UTC) Date: Sat, 9 Nov 2019 20:52:29 +0000 (UTC) From: Christopher Lameter X-X-Sender: cl@www.lameter.com To: Yu Zhao cc: Pekka Enberg , David Rientjes , Joonsoo Kim , Andrew Morton , "Kirill A . Shutemov" , Tetsuo Handa , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A . Shutemov" Subject: Re: [PATCH v4 2/2] mm: avoid slub allocation while holding list_lock In-Reply-To: <20191108193958.205102-2-yuzhao@google.com> Message-ID: References: <20190914000743.182739-1-yuzhao@google.com> <20191108193958.205102-1-yuzhao@google.com> <20191108193958.205102-2-yuzhao@google.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII 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 Fri, 8 Nov 2019, 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. How did this happen? The kmalloc needs to be always done before the list_lock is taken. > Fixing the problem by using a static bitmap instead. > > 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 *** Ahh. list_slab_objects() in shutdown? There is a much easier fix for this: [FIX] slub: Remove kmalloc under list_lock from list_slab_objects() list_slab_objects() is called when a slab is destroyed and there are objects still left to list the objects in the syslog. This is a pretty rare event. And there it seems we take the list_lock and call kmalloc while holding that lock. Perform the allocation in free_partial() before the list_lock is taken. Fixes: bbd7d57bfe852d9788bae5fb171c7edb4021d8ac ("slub: Potential stack overflow") Signed-off-by: Christoph Lameter Index: linux/mm/slub.c =================================================================== --- linux.orig/mm/slub.c 2019-10-15 13:54:57.032655296 +0000 +++ linux/mm/slub.c 2019-11-09 20:43:52.374187381 +0000 @@ -3690,14 +3690,11 @@ error: } static void list_slab_objects(struct kmem_cache *s, struct page *page, - const char *text) + const char *text, unsigned long *map) { #ifdef CONFIG_SLUB_DEBUG void *addr = page_address(page); void *p; - unsigned long *map = bitmap_zalloc(page->objects, GFP_ATOMIC); - if (!map) - return; slab_err(s, page, text, s->name); slab_lock(page); @@ -3723,6 +3720,10 @@ static void free_partial(struct kmem_cac { LIST_HEAD(discard); struct page *page, *h; + unsigned long *map = bitmap_alloc(oo_objects(s->max), GFP_KERNEL); + + if (!map) + return; BUG_ON(irqs_disabled()); spin_lock_irq(&n->list_lock); @@ -3732,7 +3733,8 @@ static void free_partial(struct kmem_cac list_add(&page->slab_list, &discard); } else { list_slab_objects(s, page, - "Objects remaining in %s on __kmem_cache_shutdown()"); + "Objects remaining in %s on __kmem_cache_shutdown()", + map); } } spin_unlock_irq(&n->list_lock);