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=-4.0 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 00691C47423 for ; Sun, 27 Sep 2020 23:35:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id AE8A720715 for ; Sun, 27 Sep 2020 23:35:31 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="F/56Xv83" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726469AbgI0Xf3 (ORCPT ); Sun, 27 Sep 2020 19:35:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43606 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726414AbgI0Xf3 (ORCPT ); Sun, 27 Sep 2020 19:35:29 -0400 Received: from mail-qv1-xf41.google.com (mail-qv1-xf41.google.com [IPv6:2607:f8b0:4864:20::f41]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E6B9DC0613D5 for ; Sun, 27 Sep 2020 16:35:28 -0700 (PDT) Received: by mail-qv1-xf41.google.com with SMTP id f11so4547886qvw.3 for ; Sun, 27 Sep 2020 16:35:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=QZ9ccKxrbw+GLDZtn/A5B8mgsLI26ygsTihNFMKsaJg=; b=F/56Xv83N6WX7oppzzL1NJZmCHsucSUClxFHBoBH3xsnTVfETiPJeuhnRdxGz41V4r wmhjN4hzByPXiI41LvOfaV3oAVNMOhh4n5Bti5j3pJHKbA2Nsm8f9J/+OQapxcZKM/0E Yg72rxpPjAQYXHf+wlNQils/SLD473ptBw7hc= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=QZ9ccKxrbw+GLDZtn/A5B8mgsLI26ygsTihNFMKsaJg=; b=kmGJjsWp/HQCXBZ7If8ZcDk3Lhgull+Hu3LeyWMkZNp+dppBySnXCxDB/w4I+Wtohn fmBMoW35O0uvfRmOb2YSn4egwlRBvByYWxkDPUAl0Y9DW+19vKK1QfLsyiB5WmlIsM8d D5cPdeJOPcnwSIT6TZZ44tXXkWj0qUUydMwvTMSxj/xew3vnP+4JJw4odDqz2BM7CBAL Wcs9bCLapyfiIr9rlQ7+y8eEUz8V/XDvDo0SDUPy+8wJ8tMNYy1BVDF8cNKCkJE7QNGi kS4RrD7RJdcHlZ3uqmMlV6dixnkGDlLW+7MA+e0+1xubEaA+2ShHRZCdV/EKwb8bJ64k 9FxQ== X-Gm-Message-State: AOAM532XqkhvkYql8OXp4IVl3wyNvmWdesZf/GSLKwXqutmxexVQrgCx QPQCd0Uer/litWE0wJA44fulVQ== X-Google-Smtp-Source: ABdhPJxVvYjhgGsi9+tR/TAw2u5qjrv6jp+i1+M0SKg/XJH2jhzXZSe5R7zNVYtzRKNJD4xFiXfYRw== X-Received: by 2002:a05:6214:292:: with SMTP id l18mr9219493qvv.3.1601249727784; Sun, 27 Sep 2020 16:35:27 -0700 (PDT) Received: from localhost ([2620:15c:6:12:cad3:ffff:feb3:bd59]) by smtp.gmail.com with ESMTPSA id j16sm7589014qkg.26.2020.09.27.16.35.27 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 27 Sep 2020 16:35:27 -0700 (PDT) Date: Sun, 27 Sep 2020 19:35:26 -0400 From: Joel Fernandes To: Shuah Khan Cc: corbet@lwn.net, keescook@chromium.org, gregkh@linuxfoundation.org, shuah@kernel.org, rafael@kernel.org, johannes@sipsolutions.net, lenb@kernel.org, james.morse@arm.com, tony.luck@intel.com, bp@alien8.de, arve@android.com, tkjos@android.com, maco@android.com, christian@brauner.io, hridya@google.com, surenb@google.com, minyard@acm.org, arnd@arndb.de, mchehab@kernel.org, rric@kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-acpi@vger.kernel.org, devel@driverdev.osuosl.org, openipmi-developer@lists.sourceforge.net, linux-edac@vger.kernel.org Subject: Re: [PATCH 00/11] Introduce Simple atomic and non-atomic counters Message-ID: <20200927233526.GA500818@google.com> References: 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-edac@vger.kernel.org On Fri, Sep 25, 2020 at 05:47:14PM -0600, Shuah Khan wrote: > This patch series is a result of discussion at the refcount_t BOF > the Linux Plumbers Conference. In this discussion, we identified > a need for looking closely and investigating atomic_t usages in > the kernel when it is used strictly as a counter without it > controlling object lifetimes and state changes. > > There are a number of atomic_t usages in the kernel where atomic_t api > is used strictly for counting and not for managing object lifetime. In > some cases, atomic_t might not even be needed. > > The purpose of these counters is twofold: 1. clearly differentiate > atomic_t counters from atomic_t usages that guard object lifetimes, > hence prone to overflow and underflow errors. It allows tools that scan > for underflow and overflow on atomic_t usages to detect overflow and > underflows to scan just the cases that are prone to errors. 2. provides > non-atomic counters for cases where atomic isn't necessary. Nice series :) It appears there is no user of counter_simple in this series other than the selftest. Would you be planning to add any conversions in the series itself, for illustration of use? Sorry if I missed a usage. Also how do we guard against atomicity of counter_simple RMW operations? Is the implication that it should be guarded using other synchronization to prevent lost-update problem? Some more comments: 1. atomic RMW operations that have a return value are fully ordered. Would you be adding support to counter_simple for such ordering as well, for consistency? 2. I felt counter_atomic and counter_atomic64 would be nice equivalents to the atomic and atomic64 naming currently used (i.e. dropping the '32'). However that is just my opinion and I am ok with either naming. thanks! - Joel > > Simple atomic and non-atomic counters api provides interfaces for simple > atomic and non-atomic counters that just count, and don't guard resource > lifetimes. Counters will wrap around to 0 when it overflows and should > not be used to guard resource lifetimes, device usage and open counts > that control state changes, and pm states. > > Using counter_atomic to guard lifetimes could lead to use-after free > when it overflows and undefined behavior when used to manage state > changes and device usage/open states. > > This patch series introduces Simple atomic and non-atomic counters. > Counter atomic ops leverage atomic_t and provide a sub-set of atomic_t > ops. > > In addition this patch series converts a few drivers to use the new api. > The following criteria is used for select variables for conversion: > > 1. Variable doesn't guard object lifetimes, manage state changes e.g: > device usage counts, device open counts, and pm states. > 2. Variable is used for stats and counters. > 3. The conversion doesn't change the overflow behavior. > > Changes since RFC: > -- Thanks for reviews and reviewed-by, and Acked-by tags. Updated > the patches with the tags. > -- Addressed Kees's comments: > 1. Non-atomic counters renamed to counter_simple32 and counter_simple64 > to clearly indicate size. > 2. Added warning for counter_simple* usage and it should be used only > when there is no need for atomicity. > 3. Renamed counter_atomic to counter_atomic32 to clearly indicate size. > 4. Renamed counter_atomic_long to counter_atomic64 and it now uses > atomic64_t ops and indicates size. > 5. Test updated for the API renames. > 6. Added helper functions for test results printing > 7. Verified that the test module compiles in kunit env. and test > module can be loaded to run the test. > 8. Updated Documentation to reflect the intent to make the API > restricted so it can never be used to guard object lifetimes > and state management. I left _return ops for now, inc_return > is necessary for now as per the discussion we had on this topic. > -- Updated driver patches with API name changes. > -- We discussed if binder counters can be non-atomic. For now I left > them the same as the RFC patch - using counter_atomic32 > -- Unrelated to this patch series: > The patch series review uncovered improvements could be made to > test_async_driver_probe and vmw_vmci/vmci_guest. I will track > these for fixing later. > > Shuah Khan (11): > counters: Introduce counter_simple* and counter_atomic* counters > selftests:lib:test_counters: add new test for counters > drivers/base: convert deferred_trigger_count and probe_count to > counter_atomic32 > drivers/base/devcoredump: convert devcd_count to counter_atomic32 > drivers/acpi: convert seqno counter_atomic32 > drivers/acpi/apei: convert seqno counter_atomic32 > drivers/android/binder: convert stats, transaction_log to > counter_atomic32 > drivers/base/test/test_async_driver_probe: convert to use > counter_atomic32 > drivers/char/ipmi: convert stats to use counter_atomic32 > drivers/misc/vmw_vmci: convert num guest devices counter to > counter_atomic32 > drivers/edac: convert pci counters to counter_atomic32 > > Documentation/core-api/counters.rst | 174 +++++++++ > MAINTAINERS | 8 + > drivers/acpi/acpi_extlog.c | 5 +- > drivers/acpi/apei/ghes.c | 5 +- > drivers/android/binder.c | 41 +-- > drivers/android/binder_internal.h | 3 +- > drivers/base/dd.c | 19 +- > drivers/base/devcoredump.c | 5 +- > drivers/base/test/test_async_driver_probe.c | 23 +- > drivers/char/ipmi/ipmi_msghandler.c | 9 +- > drivers/char/ipmi/ipmi_si_intf.c | 9 +- > drivers/edac/edac_pci.h | 5 +- > drivers/edac/edac_pci_sysfs.c | 28 +- > drivers/misc/vmw_vmci/vmci_guest.c | 9 +- > include/linux/counters.h | 350 +++++++++++++++++++ > lib/Kconfig | 10 + > lib/Makefile | 1 + > lib/test_counters.c | 276 +++++++++++++++ > tools/testing/selftests/lib/Makefile | 1 + > tools/testing/selftests/lib/config | 1 + > tools/testing/selftests/lib/test_counters.sh | 5 + > 21 files changed, 913 insertions(+), 74 deletions(-) > create mode 100644 Documentation/core-api/counters.rst > create mode 100644 include/linux/counters.h > create mode 100644 lib/test_counters.c > create mode 100755 tools/testing/selftests/lib/test_counters.sh > > -- > 2.25.1 >