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=-8.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 7D798C43381 for ; Wed, 27 Mar 2019 17:30:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 52E5B206B7 for ; Wed, 27 Mar 2019 17:30:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728566AbfC0RaD (ORCPT ); Wed, 27 Mar 2019 13:30:03 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:58366 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726803AbfC0RaC (ORCPT ); Wed, 27 Mar 2019 13:30:02 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 543CD80D; Wed, 27 Mar 2019 10:30:02 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 63F773F557; Wed, 27 Mar 2019 10:30:00 -0700 (PDT) Date: Wed, 27 Mar 2019 17:29:57 +0000 From: Catalin Marinas To: Michal Hocko Cc: Qian Cai , akpm@linux-foundation.org, cl@linux.com, willy@infradead.org, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] kmemleak: survive in a low-memory situation Message-ID: <20190327172955.GB17247@arrakis.emea.arm.com> References: <20190327005948.24263-1-cai@lca.pw> <20190327084432.GA11927@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190327084432.GA11927@dhcp22.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Mar 27, 2019 at 09:44:32AM +0100, Michal Hocko wrote: > On Tue 26-03-19 20:59:48, Qian Cai wrote: > [...] > > Unless there is a brave soul to reimplement the kmemleak to embed it's > > metadata into the tracked memory itself in a foreseeable future, Revisiting the kmemleak memory scanning code, that's not actually possible without some long periods with kmemleak_lock held. The scanner relies on the kmemleak_object (refcounted) being around even when the actual memory block has been freed. > > this > > provides a good balance between enabling kmemleak in a low-memory > > situation and not introducing too much hackiness into the existing > > code for now. Another approach is to fail back the original allocation > > once kmemleak_alloc() failed, but there are too many call sites to > > deal with which makes it error-prone. > > As long as there is an implicit __GFP_NOFAIL then kmemleak is simply > broken no matter what other gfp flags you play with. Has anybody looked > at some sort of preallocation where gfpflags_allow_blocking context > allocate objects into a pool that non-sleeping allocations can eat from? Quick attempt below and it needs some more testing (pretty random pick of the EMERGENCY_POOL_SIZE value). Also, with __GFP_NOFAIL removed, are the other flags safe or we should trim them further? ---------------8<------------------------------- >From dc4194539f8191bb754901cea74c86e7960886f8 Mon Sep 17 00:00:00 2001 From: Catalin Marinas Date: Wed, 27 Mar 2019 17:20:57 +0000 Subject: [PATCH] mm: kmemleak: Add an emergency allocation pool for kmemleak objects This patch adds an emergency pool for struct kmemleak_object in case the normal kmem_cache_alloc() fails under the gfp constraints passed by the slab allocation caller. The patch also removes __GFP_NOFAIL which does not play well with other gfp flags (introduced by commit d9570ee3bd1d, "kmemleak: allow to coexist with fault injection"). Suggested-by: Michal Hocko Signed-off-by: Catalin Marinas --- mm/kmemleak.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 57 insertions(+), 2 deletions(-) diff --git a/mm/kmemleak.c b/mm/kmemleak.c index 6c318f5ac234..366a680cff7c 100644 --- a/mm/kmemleak.c +++ b/mm/kmemleak.c @@ -127,7 +127,7 @@ /* GFP bitmask for kmemleak internal allocations */ #define gfp_kmemleak_mask(gfp) (((gfp) & (GFP_KERNEL | GFP_ATOMIC)) | \ __GFP_NORETRY | __GFP_NOMEMALLOC | \ - __GFP_NOWARN | __GFP_NOFAIL) + __GFP_NOWARN) /* scanning area inside a memory block */ struct kmemleak_scan_area { @@ -191,11 +191,16 @@ struct kmemleak_object { #define HEX_ASCII 1 /* max number of lines to be printed */ #define HEX_MAX_LINES 2 +/* minimum emergency pool size */ +#define EMERGENCY_POOL_SIZE (NR_CPUS * 4) /* the list of all allocated objects */ static LIST_HEAD(object_list); /* the list of gray-colored objects (see color_gray comment below) */ static LIST_HEAD(gray_list); +/* emergency pool allocation */ +static LIST_HEAD(emergency_list); +static int emergency_pool_size; /* search tree for object boundaries */ static struct rb_root object_tree_root = RB_ROOT; /* rw_lock protecting the access to object_list and object_tree_root */ @@ -467,6 +472,43 @@ static int get_object(struct kmemleak_object *object) return atomic_inc_not_zero(&object->use_count); } +/* + * Emergency pool allocation and freeing. kmemleak_lock must not be held. + */ +static struct kmemleak_object *emergency_alloc(void) +{ + unsigned long flags; + struct kmemleak_object *object; + + write_lock_irqsave(&kmemleak_lock, flags); + object = list_first_entry_or_null(&emergency_list, typeof(*object), object_list); + if (object) { + list_del(&object->object_list); + emergency_pool_size--; + } + write_unlock_irqrestore(&kmemleak_lock, flags); + + return object; +} + +/* + * Return true if object added to the emergency pool, false otherwise. + */ +static bool emergency_free(struct kmemleak_object *object) +{ + unsigned long flags; + + if (emergency_pool_size >= EMERGENCY_POOL_SIZE) + return false; + + write_lock_irqsave(&kmemleak_lock, flags); + list_add(&object->object_list, &emergency_list); + emergency_pool_size++; + write_unlock_irqrestore(&kmemleak_lock, flags); + + return true; +} + /* * RCU callback to free a kmemleak_object. */ @@ -485,7 +527,8 @@ static void free_object_rcu(struct rcu_head *rcu) hlist_del(&area->node); kmem_cache_free(scan_area_cache, area); } - kmem_cache_free(object_cache, object); + if (!emergency_free(object)) + kmem_cache_free(object_cache, object); } /* @@ -577,6 +620,8 @@ static struct kmemleak_object *create_object(unsigned long ptr, size_t size, unsigned long untagged_ptr; object = kmem_cache_alloc(object_cache, gfp_kmemleak_mask(gfp)); + if (!object) + object = emergency_alloc(); if (!object) { pr_warn("Cannot allocate a kmemleak_object structure\n"); kmemleak_disable(); @@ -2127,6 +2172,16 @@ void __init kmemleak_init(void) kmemleak_warning = 0; } } + + /* populate the emergency allocation pool */ + while (emergency_pool_size < EMERGENCY_POOL_SIZE) { + struct kmemleak_object *object; + + object = kmem_cache_alloc(object_cache, GFP_KERNEL); + if (!object) + break; + emergency_free(object); + } } /*