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=-9.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 AF6DCC4360F for ; Tue, 2 Apr 2019 03:31:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 72D67207E0 for ; Tue, 2 Apr 2019 03:31:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1554175879; bh=FE/eNTVVmkZpNxedhTlxMNBvv1R+8n1pzmyI1KBQOMI=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=c/zxZ5OK+44ULB8DOyBtdRALC7/+SfqFXc0qbEV6LxgBA7dM31ZjEc4mkJwtmSE51 dlfyAIFrWNuKubEARIwPI9HTnmN4WdOc0Zw4f/vqVhf8CdvY5LpEvNyej+lZDJhzTk HrLXQP8wHPjIuT0BOLVc8PwUYnPB0NZwfpou273k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729122AbfDBDbS (ORCPT ); Mon, 1 Apr 2019 23:31:18 -0400 Received: from out2-smtp.messagingengine.com ([66.111.4.26]:34481 "EHLO out2-smtp.messagingengine.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726501AbfDBDbR (ORCPT ); Mon, 1 Apr 2019 23:31:17 -0400 Received: from compute3.internal (compute3.nyi.internal [10.202.2.43]) by mailout.nyi.internal (Postfix) with ESMTP id 7444822246; Mon, 1 Apr 2019 23:31:15 -0400 (EDT) Received: from mailfrontend2 ([10.202.2.163]) by compute3.internal (MEProxy); Mon, 01 Apr 2019 23:31:15 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:content-transfer-encoding:date:from :in-reply-to:message-id:mime-version:references:subject:to :x-me-proxy:x-me-proxy:x-me-sender:x-me-sender:x-sasl-enc; s= fm2; bh=qS74YLv32TK4OdRxyP79l+k5LQKLZkF6HF7u7XLPsVY=; b=J08A5mJb UVl31TB6lBjTNCDo3r2bk4xwTFtJIQ9a+1YCHSkj1oQGYW7B3uWXxsbHyGIoyaY6 1cSMIi8SOQdEFgMG3V1puLlXCNvSlftMGeu4BP1PPbcyeVt1+CFXp/GljiqrGZ0Y hsuDAsRcHfDYGAaJCmkVuwj1wU9Kg+588EQPWr8MFpUTH8BJA8/JDQ0Ldap/S9F8 +yTfqCBElrEHZlrL72Ngk6jd6gw9WFdY65Fvbrr8mHQB5yd/8MwpBE6rPxOMQUsW z2l/Jb4UG2O/9BpRfOnjSdL9RQYz4oP30CF+IwA0i1PCrw/JeY5J69iOE9vfwE8H EQpqkROtgrjsDQ== X-ME-Sender: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedutddrleehgdeikecutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpefhvffufffkofgjfhgggfestdekredtredttdenucfhrhhomhepfdfvohgsihhn ucevrdcujfgrrhguihhnghdfuceothhosghinheskhgvrhhnvghlrdhorhhgqeenucfkph epuddvgedrudejuddrvdefrdduvddvnecurfgrrhgrmhepmhgrihhlfhhrohhmpehtohgs ihhnsehkvghrnhgvlhdrohhrghenucevlhhushhtvghrufhiiigvpedt X-ME-Proxy: Received: from eros.localdomain (124-171-23-122.dyn.iinet.net.au [124.171.23.122]) by mail.messagingengine.com (Postfix) with ESMTPA id 549AC100E5; Mon, 1 Apr 2019 23:31:11 -0400 (EDT) From: "Tobin C. Harding" To: Andrew Morton Cc: "Tobin C. Harding" , LKP , Roman Gushchin , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , Matthew Wilcox , linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel test robot Subject: [PATCH 1/1] slob: Only use list functions when safe to do so Date: Tue, 2 Apr 2019 14:29:57 +1100 Message-Id: <20190402032957.26249-2-tobin@kernel.org> X-Mailer: git-send-email 2.21.0 In-Reply-To: <20190402032957.26249-1-tobin@kernel.org> References: <20190402032957.26249-1-tobin@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently we call (indirectly) list_del() then we manually try to combat the fact that the list may be in an undefined state by getting 'prev' and 'next' pointers in a somewhat contrived manner. It is hard to verify that this works for all initial states of the list. Clearly the author (me) got it wrong the first time because the 0day kernel testing robot managed to crash the kernel thanks to this code. All this is done in order to do an optimisation aimed at preventing fragmentation at the start of a slab. We can just skip this optimisation any time the list is put into an undefined state since this only occurs when an allocation completely fills the slab and in this case the optimisation is unnecessary since we have not fragmented the slab by this allocation. Change the page pointer passed to slob_alloc_page() to be a double pointer so that we can set it to NULL to indicate that the page was removed from the list. Skip the optimisation if the page was removed. Found thanks to the kernel test robot, email subject: 340d3d6178 ("mm/slob.c: respect list_head abstraction layer"): kernel BUG at lib/list_debug.c:31! Reported-by: kernel test robot Signed-off-by: Tobin C. Harding --- mm/slob.c | 50 ++++++++++++++++++++++++++++++-------------------- 1 file changed, 30 insertions(+), 20 deletions(-) diff --git a/mm/slob.c b/mm/slob.c index 21af3fdb457a..c543da10df45 100644 --- a/mm/slob.c +++ b/mm/slob.c @@ -213,10 +213,18 @@ static void slob_free_pages(void *b, int order) } /* - * Allocate a slob block within a given slob_page sp. + * slob_page_alloc() - Allocate a slob block within a given slob_page sp. + * @spp: Page to look in, return parameter. + * @size: Size of the allocation. + * @align: Allocation alignment. + * + * Tries to find a chunk of memory at least @size within page. If the + * allocation fills up page then page is removed from list, in this case + * *spp will be set to %NULL to signal that list removal occurred. */ -static void *slob_page_alloc(struct page *sp, size_t size, int align) +static void *slob_page_alloc(struct page **spp, size_t size, int align) { + struct page *sp = *spp; slob_t *prev, *cur, *aligned = NULL; int delta = 0, units = SLOB_UNITS(size); @@ -254,8 +262,11 @@ static void *slob_page_alloc(struct page *sp, size_t size, int align) } sp->units -= units; - if (!sp->units) + if (!sp->units) { clear_slob_page_free(sp); + /* Signal that page was removed from list. */ + *spp = NULL; + } return cur; } if (slob_last(cur)) @@ -268,7 +279,7 @@ static void *slob_page_alloc(struct page *sp, size_t size, int align) */ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node) { - struct page *sp, *prev, *next; + struct page *sp; struct list_head *slob_list; slob_t *b = NULL; unsigned long flags; @@ -283,6 +294,7 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node) spin_lock_irqsave(&slob_lock, flags); /* Iterate through each partially free page, try to find room */ list_for_each_entry(sp, slob_list, slab_list) { + struct page **spp = &sp; #ifdef CONFIG_NUMA /* * If there's a node specification, search for a partial @@ -295,27 +307,25 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node) if (sp->units < SLOB_UNITS(size)) continue; - /* - * Cache previous entry because slob_page_alloc() may - * remove sp from slob_list. - */ - prev = list_prev_entry(sp, slab_list); - /* Attempt to alloc */ - b = slob_page_alloc(sp, size, align); + b = slob_page_alloc(spp, size, align); if (!b) continue; - next = list_next_entry(prev, slab_list); /* This may or may not be sp */ - /* - * Improve fragment distribution and reduce our average - * search time by starting our next search here. (see - * Knuth vol 1, sec 2.5, pg 449) + * If slob_page_alloc() removed sp from the list then we + * cannot call list functions on sp. Just bail, don't + * worry about the optimisation below. */ - if (!list_is_first(&next->slab_list, slob_list)) - list_rotate_to_front(&next->slab_list, slob_list); - + if (*spp) { + /* + * Improve fragment distribution and reduce our average + * search time by starting our next search here. (see + * Knuth vol 1, sec 2.5, pg 449) + */ + if (!list_is_first(&sp->slab_list, slob_list)) + list_rotate_to_front(&sp->slab_list, slob_list); + } break; } spin_unlock_irqrestore(&slob_lock, flags); @@ -334,7 +344,7 @@ static void *slob_alloc(size_t size, gfp_t gfp, int align, int node) INIT_LIST_HEAD(&sp->slab_list); set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE)); set_slob_page_free(sp, slob_list); - b = slob_page_alloc(sp, size, align); + b = slob_page_alloc(&sp, size, align); BUG_ON(!b); spin_unlock_irqrestore(&slob_lock, flags); } -- 2.21.0