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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8FB34C04E69 for ; Mon, 14 Aug 2023 16:22:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232036AbjHNQVj (ORCPT ); Mon, 14 Aug 2023 12:21:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:52468 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230348AbjHNQVE (ORCPT ); Mon, 14 Aug 2023 12:21:04 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2290CF1 for ; Mon, 14 Aug 2023 09:21:03 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id B4823621AB for ; Mon, 14 Aug 2023 16:21:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7E82DC433C7; Mon, 14 Aug 2023 16:21:00 +0000 (UTC) Date: Mon, 14 Aug 2023 17:20:58 +0100 From: Catalin Marinas To: Vlastimil Babka Cc: wang xiaolei , akpm@linux-foundation.org, glider@google.com, andreyknvl@gmail.com, zhaoyang.huang@unisoc.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] mm/kmemleak: No need to check kmemleak_initialized in set_track_prepare() Message-ID: References: <20230810074704.2042664-1-xiaolei.wang@windriver.com> <20230810074704.2042664-3-xiaolei.wang@windriver.com> <37397d75-c95c-8730-cf22-79e283e0bd6c@suse.cz> <79deae0c-eeef-2370-9d8a-b2746389d38c@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 11, 2023 at 10:09:08AM +0200, Vlastimil Babka wrote: > On 8/11/23 04:03, wang xiaolei wrote: > > On 8/10/23 9:16 PM, Vlastimil Babka wrote: > >> Looking closer, I think what you want could be achieved by kmemleak_init() > >> setting a variable that is checked in kmemleak_initialized() instead of the > >> kmemleak_initialized that's set too late. > >> > >> I think this should work because: > >> - I assume kmemleak can't record anything before kmemleak_init() > >> - stack depot early init is requested one way or the other > >> - mm_core_init() calls stack_depot_early_init() before kmemleak_init() > >> > >> But I also wonder how kmemleak can even reach set_track_prepare() before > >> kmemleak_init(), maybe that's the issue? > > > > Before kmemleak_init, many places also need to allocate kmemleak_object, > > > > and also need to save stack in advance, but kmemleak_object is allocated > > > > in the form of an array, after kmemleak_init 'object_cache = > > KMEM_CACHE(kmemleak_object, SLAB_NOLEAKTRACE);' > > Hm I see, kmemleak has this static mempool so it really can record some > objects very early. Indeed, otherwise we'd get a lot of false positives. > > I think there is still some memory not recorded on the backtrace before > > > > stack_depot_early_init(), does anyone have a better suggestion? > > No we can't record the backtrace earlier. But I don't think it's a problem > in practice. AFAIU kmemleak needs to record these very early allocations so > if they point to further objects, those are not suspected as orphans. But > the early allocations themselves also are very unlikely to be leaks, so does > it really matter that we don't have a backtrace for their allocation? > Because the backtrace is the only thing that's missing - the object is > otherwise recorded even if set_track_prepare() returns 0. It's not a functional problem, just a reporting one. There are rare early leaks (usually false positives) so identifying them would help. That said, I think set_track_prepare() is too conservative in waiting for kmemleak_initialized to be set in kmemleak_late_init(). That's a late_initcall() meant for the scanning thread etc. not the core kmemleak functionality (which is on from early boot). We can instead use a different variable to check in set_track_prepare(), e.g. object_cache. stack_depot_early_init() is called prior to kmemleak_init(), so it should be fine. If "kmemleak_initialized" is confusing, we could rename it to "kmemleak_late_initialized" or "kmemleak_fully_initialized". I'm not too fussed about this as long as we add some comment on why we check object_cache instead of kmemleak_initialized. -- Catalin