From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 7B8246B0279 for ; Wed, 24 May 2017 12:52:21 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id t12so116213323pgo.7 for ; Wed, 24 May 2017 09:52:21 -0700 (PDT) Received: from foss.arm.com (foss.arm.com. [217.140.101.70]) by mx.google.com with ESMTP id 31si24594329plk.66.2017.05.24.09.52.20 for ; Wed, 24 May 2017 09:52:20 -0700 (PDT) Date: Wed, 24 May 2017 17:52:14 +0100 From: Catalin Marinas Subject: Re: [PATCH] mm: kmemleak: Treat vm_struct as alternative reference to vmalloc'ed objects Message-ID: <20170524165214.GF19448@e104818-lin.cambridge.arm.com> References: <1495474514-24425-1-git-send-email-catalin.marinas@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Andy Lutomirski Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Michal Hocko , "Luis R. Rodriguez" On Mon, May 22, 2017 at 11:19:08AM -0700, Andy Lutomirski wrote: > On Mon, May 22, 2017 at 10:35 AM, Catalin Marinas > wrote: > > Kmemleak requires that vmalloc'ed objects have a minimum reference count > > of 2: one in the corresponding vm_struct object and the other owned by > > the vmalloc() caller. There are cases, however, where the original > > vmalloc() returned pointer is lost and, instead, a pointer to vm_struct > > is stored (see free_thread_stack()). Kmemleak currently reports such > > objects as leaks. > > > > This patch adds support for treating any surplus references to an object > > as additional references to a specified object. It introduces the > > kmemleak_vmalloc() API function which takes a vm_struct pointer and sets > > its surplus reference passing to the actual vmalloc() returned pointer. > > The __vmalloc_node_range() calling site has been modified accordingly. > > > > An unrelated minor change is included in this patch to change the type > > of kmemleak_object.flags to unsigned int (previously unsigned long). > > > > Reported-by: "Luis R. Rodriguez" > > Cc: Michal Hocko > > Cc: Andy Lutomirski > > Signed-off-by: Catalin Marinas > > --- > > > > As per [1], I added support to use pointers to vm_struct as an > > alternative way to avoid false positives when the original vmalloc() > > pointer has been lost. This is slightly harder to reason about but it > > seems to work for this use-case. I'm not aware of other cases (than > > free_thread_stack()) where the original vmalloc() pointer is removed in > > favour of a vm_struct one. > > > > An alternative implementation (simpler to understand), if preferred, is > > to annotate alloc_thread_stack_node() and free_thread_stack() with > > kmemleak_unignore()/kmemleak_ignore() calls and proper comments. > > > > I personally prefer the option in this patch. It keeps the special > case in kmemleak and the allocation code rather than putting it in the > consumer code. > > Also, I want to add an API at some point that vmallocs some memory and > returns the vm_struct directly. That won't work with explicit > annotations in the caller because kmemleak might think it's leaked > before the caller can execute the annotations. While kmemleak delays the reporting of newly allocated objects to avoid such race, we need to keep annotations to a minimum anyway (only for special cases, definitely not for each caller of an allocation API). The proposed kmemleak_vmalloc() API in this patch would cover your case without any additional annotation. -- Catalin -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org