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=-8.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,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 E8AFAC31E48 for ; Wed, 12 Jun 2019 15:53:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CCE8821019 for ; Wed, 12 Jun 2019 15:53:16 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2440145AbfFLPxP (ORCPT ); Wed, 12 Jun 2019 11:53:15 -0400 Received: from bhuna.collabora.co.uk ([46.235.227.227]:46846 "EHLO bhuna.collabora.co.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2409452AbfFLPxP (ORCPT ); Wed, 12 Jun 2019 11:53:15 -0400 Received: from turingmachine.home (unknown [IPv6:2804:431:d719:d9b5:d711:794d:1c68:5ed3]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: tonyk) by bhuna.collabora.co.uk (Postfix) with ESMTPSA id 0E7D52808F4; Wed, 12 Jun 2019 16:53:10 +0100 (BST) From: =?UTF-8?q?Andr=C3=A9=20Almeida?= To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, catalin.marinas@arm.com, kernel@collabora.com, akpm@linux-foundation.org, =?UTF-8?q?Andr=C3=A9=20Almeida?= Subject: [PATCH v2 2/2] docs: kmemleak: add more documentation details Date: Wed, 12 Jun 2019 12:52:31 -0300 Message-Id: <20190612155231.19448-2-andrealmeid@collabora.com> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190612155231.19448-1-andrealmeid@collabora.com> References: <20190612155231.19448-1-andrealmeid@collabora.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Wikipedia now has a main article to "tracing garbage collector" topic. Change the URL and use the reStructuredText syntax for hyperlinks and add more details about the use of the tool. Add a section about how to use the kmemleak-test module to test the memory leak scanning. Signed-off-by: André Almeida --- Changes in v2: none Documentation/dev-tools/kmemleak.rst | 48 +++++++++++++++++++++++++--- 1 file changed, 44 insertions(+), 4 deletions(-) diff --git a/Documentation/dev-tools/kmemleak.rst b/Documentation/dev-tools/kmemleak.rst index e6f51260ff32..3621cd5e1eef 100644 --- a/Documentation/dev-tools/kmemleak.rst +++ b/Documentation/dev-tools/kmemleak.rst @@ -2,8 +2,8 @@ Kernel Memory Leak Detector =========================== Kmemleak provides a way of detecting possible kernel memory leaks in a -way similar to a tracing garbage collector -(https://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29#Tracing_garbage_collectors), +way similar to a `tracing garbage collector +`_, with the difference that the orphan objects are not freed but only reported via /sys/kernel/debug/kmemleak. A similar method is used by the Valgrind tool (``memcheck --leak-check``) to detect the memory leaks in @@ -15,10 +15,13 @@ Usage CONFIG_DEBUG_KMEMLEAK in "Kernel hacking" has to be enabled. A kernel thread scans the memory every 10 minutes (by default) and prints the -number of new unreferenced objects found. To display the details of all -the possible memory leaks:: +number of new unreferenced objects found. If the ``debugfs`` isn't already +mounted, mount with:: # mount -t debugfs nodev /sys/kernel/debug/ + +To display the details of all the possible scanned memory leaks:: + # cat /sys/kernel/debug/kmemleak To trigger an intermediate memory scan:: @@ -72,6 +75,9 @@ If CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF are enabled, the kmemleak is disabled by default. Passing ``kmemleak=on`` on the kernel command line enables the function. +If you are getting errors like "Error while writing to stdout" or "write_loop: +Invalid argument", make sure kmemleak is properly enabled. + Basic Algorithm --------------- @@ -218,3 +224,37 @@ the pointer is calculated by other methods than the usual container_of macro or the pointer is stored in a location not scanned by kmemleak. Page allocations and ioremap are not tracked. + +Testing with kmemleak-test +-------------------------- + +To check if you have all set up to use kmemleak, you can use the kmemleak-test +module, a module that deliberately leaks memory. Set CONFIG_DEBUG_KMEMLEAK_TEST +as module (it can't be used as bult-in) and boot the kernel with kmemleak +enabled. Load the module and perform a scan with:: + + # modprobe kmemleak-test + # echo scan > /sys/kernel/debug/kmemleak + +Note that the you may not get results instantly or on the first scanning. When +kmemleak gets results, it'll log ``kmemleak: new suspected +memory leaks``. Then read the file to see then:: + + # cat /sys/kernel/debug/kmemleak + unreferenced object 0xffff89862ca702e8 (size 32): + comm "modprobe", pid 2088, jiffies 4294680594 (age 375.486s) + hex dump (first 32 bytes): + 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b kkkkkkkkkkkkkkkk + 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b a5 kkkkkkkkkkkkkkk. + backtrace: + [<00000000e0a73ec7>] 0xffffffffc01d2036 + [<000000000c5d2a46>] do_one_initcall+0x41/0x1df + [<0000000046db7e0a>] do_init_module+0x55/0x200 + [<00000000542b9814>] load_module+0x203c/0x2480 + [<00000000c2850256>] __do_sys_finit_module+0xba/0xe0 + [<000000006564e7ef>] do_syscall_64+0x43/0x110 + [<000000007c873fa6>] entry_SYSCALL_64_after_hwframe+0x44/0xa9 + ... + +Removing the module with ``rmmod kmemleak_test`` should also trigger some +kmemleak results. -- 2.22.0