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[23.128.96.18]) by mx.google.com with ESMTP id i7si102007ejx.34.2020.12.08.17.16.10; Tue, 08 Dec 2020 17:16:33 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@kernel.org header.s=k20201202 header.b=X9rmamK9; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726553AbgLIBMG (ORCPT + 99 others); Tue, 8 Dec 2020 20:12:06 -0500 Received: from mail.kernel.org ([198.145.29.99]:37262 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725881AbgLIBMG (ORCPT ); Tue, 8 Dec 2020 20:12:06 -0500 Date: Tue, 8 Dec 2020 17:11:24 -0800 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1607476285; bh=86Y3uT99F3tJGRc8oJiWdNyf9+evidkYld7zLrp6oNc=; h=From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=X9rmamK9/+r5LLPPa/TL37AwFxp6X6oP1JIacIvrCcMDjjwlOglfnuHCO84ayub71 KaWsORbxvFMIcoRRtKtOVNFb410+Fn5aJLHg7nqpC6qnirjOzMPDtqkNujtWKLAFZN XyeYHG7Fb4wCSowZ1Z4CGKWvFb4j4dvsdJrNpKOJcYGc3Yh+wGnB4flcDIfoEtFSSa efICFCjAIqBcAqEnEI84d75l1I46LeWTFmVLUjF+YgwgOPzanHogQpQj40gKhgUDMc qWQGgepKxwAI+58/QoA90Ul/IOD/UyvA/BL0ltwGj7zelIYy1dF4nAVPgfYSRkjPvN ro6qSb5bGe32A== From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org Subject: [PATCH RFC v2 sl-b] Export return addresses etc. for better diagnostics Message-ID: <20201209011124.GA31164@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201205004022.GA31166@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201205004022.GA31166@paulmck-ThinkPad-P72> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello! This is v2 of the series the improves diagnostics by providing access to additional information including the return addresses collected by the sl*b allocators and by vmalloc(). If the allocator is not configured to collect this information, the diagnostics fall back to a reasonable approximation of their earlier state. One use case is the queue_rcu_work() function, which might be used by any number of kernel subsystems. If the caller does back-to-back invocations of queue_rcu_work(), this constitutes a double-free bug, and (if so configured) the debug-objects system will flag this, printing the callback function. In most cases, printing this function suffices. However, for double-free bugs involving queue_rcu_work(), the RCU callback function will always be rcu_work_rcufn(), which provides almost no help to the poor person trying to find this double-free bug. The return address from the allocator of the memory containing the rcu_work structure can provide an additional valuable clue. Another use case is the percpu_ref_switch_to_atomic_rcu() function, which detects percpu_ref reference-count underflow. Unfortunately, the only data that this function has access to doesn't have much in the way of identifying characteristics. Yes, it might be possible to gain more information from a crash dump, but it is more convenient for the needed hints to be in the console log. Unfortunately, printing the return address in this case is of little help because this object is allocated from percpu_ref_init(), regardless of what part of the kernel is responsible for the reference-count underflow. However, CONFIG_STACKTRACE=y kernels (such as those enabling ftrace) using slub with debugging enabled also collect stack traces. This series therefore also provides a way of extracting these stack traces to provide additional information to those debugging percpu_ref reference-count underflows. The patches are as follows: 1. Add mem_dump_obj() to print source of memory block. 2. Make mem_dump_obj() handle NULL and zero-sized pointers. 3. Make mem_dump_obj() handle vmalloc() memory. 4. Make call_rcu() print mem_dump_obj() info for double-freed callback. 5. Dump mem_dump_obj() info upon reference-count underflow. Thanx, Paul Changes since v1: o Apply feedback from Joonsoo Kim, mostly around naming and code structure. o Apply fix suggested by Stephen Rothwell for a bug that was also located by kbuild test robot. o Add support for vmalloc(). o Add support for special pointers. o Additional rework simplifying use of mem_dump_obj(), which simplifies both the RCU and the percpu_ref uses. ------------------------------------------------------------------------ include/linux/mm.h | 2 + include/linux/slab.h | 2 + include/linux/vmalloc.h | 6 ++++ kernel/rcu/tree.c | 7 +++- lib/percpu-refcount.c | 12 ++++++-- mm/slab.c | 28 +++++++++++++++++++ mm/slab.h | 11 +++++++ mm/slab_common.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++ mm/slob.c | 7 ++++ mm/slub.c | 40 +++++++++++++++++++++++++++ mm/util.c | 44 ++++++++++++++++++++++++++---- mm/vmalloc.c | 12 ++++++++ 12 files changed, 229 insertions(+), 11 deletions(-)