From patchwork Wed Mar 10 10:41:31 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Marco Elver X-Patchwork-Id: 397050 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=-21.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT, USER_IN_DEF_DKIM_WL 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 6FD27C433E9 for ; Wed, 10 Mar 2021 10:42:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3440764FEE for ; Wed, 10 Mar 2021 10:42:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232318AbhCJKmW (ORCPT ); Wed, 10 Mar 2021 05:42:22 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38568 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232041AbhCJKlv (ORCPT ); Wed, 10 Mar 2021 05:41:51 -0500 Received: from mail-qv1-xf49.google.com (mail-qv1-xf49.google.com [IPv6:2607:f8b0:4864:20::f49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 82AD4C061762 for ; Wed, 10 Mar 2021 02:41:51 -0800 (PST) Received: by mail-qv1-xf49.google.com with SMTP id e10so12306473qvr.17 for ; Wed, 10 Mar 2021 02:41:51 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:message-id:mime-version:subject:from:to:cc; bh=CXDGXPLv4zBuXju/CY+pJKsC5gho63hQizGsKGKZIlo=; b=s8QQMW2LW/UVYVavbb8dseqF5ki4rCkHLP26JLijl8mjtrb2/K9xsn1pRuxTKkCI4A WGyH7yeNfeUXgTkHZRLKKruj4dvA8zqeAw8g9DEKxuPrIaGljnESUIgjFlOM+bCXz4tn c9bFCJzuS2ISr9LWzCXLNx+Wcm+zwSSUKC22+8M7ayZ+u40rra70SNM/qZC8LntQ8M+x LfbEJhGnYNOCsOoYIBKkY22AYCekDUpQLyniHJOCTXmbR2NjqIWEI/Q7LXtMgkQdT9PA pBMfOEGap4OIRTFxX57bGhAxB9ytAltLxLxoTVs8/M5KXEc0dKDW6iG4+bhnhlJ2Cq5H n5tw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=CXDGXPLv4zBuXju/CY+pJKsC5gho63hQizGsKGKZIlo=; b=nqThAZfwSUquUz0BnjgbgTncLnWF3OXyZEOcw/FmxRNG311h+9HsIT/NL/ZAIFOyNc Tb2xAil85bkXoVcbQJtC7pw1zdcJXPmd7JaU8+dphjYQ/qdC3w1Eh9DgjGaIJE5wTMnp pLFXrGbFgrtuhrHgItaW9K2OARsIApTfspfnWjvEVcLIux9cEgWKJyaMIg2EY9hhORDn Dlg8CwPNsyatJhMpyzKa7dY1jaJGChRdtP5eGHDMD9y0JX51QE9r91mvpg2q4ah5PgNu wegLzmBwVTx9WtMvtvsz39umm+RdRHFdQbfSIYsOZAcWtreH3HN7R7Y97g3ajBmaD9iz mbUA== X-Gm-Message-State: AOAM530Gp5P8uwy8Gccuik33GaIU/nHtcBwL9wmmeI7kSRI/Ki5kOCRY faK7JoKpQUDK58CunjPr+wlbU7f+7w== X-Google-Smtp-Source: ABdhPJyUi3y7lpUQnvLHzVb9XkNgXOybwzuc9DsNWma/PHqm9SowojQnqTCgLARpnGj2C/XeILIJohc7NA== X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:e995:ac0b:b57c:49a4]) (user=elver job=sendgmr) by 2002:a05:6214:2262:: with SMTP id gs2mr2155838qvb.32.1615372910698; Wed, 10 Mar 2021 02:41:50 -0800 (PST) Date: Wed, 10 Mar 2021 11:41:31 +0100 Message-Id: <20210310104139.679618-1-elver@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.30.1.766.gb4fecdf3b7-goog Subject: [PATCH RFC v2 0/8] Add support for synchronous signals on perf events From: Marco Elver To: elver@google.com, peterz@infradead.org, alexander.shishkin@linux.intel.com, acme@kernel.org, mingo@redhat.com, jolsa@redhat.com, mark.rutland@arm.com, namhyung@kernel.org, tglx@linutronix.de Cc: glider@google.com, viro@zeniv.linux.org.uk, arnd@arndb.de, christian@brauner.io, dvyukov@google.com, jannh@google.com, axboe@kernel.dk, mascasa@google.com, pcc@google.com, irogers@google.com, kasan-dev@googlegroups.com, linux-arch@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-kselftest@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kselftest@vger.kernel.org The perf subsystem today unifies various tracing and monitoring features, from both software and hardware. One benefit of the perf subsystem is automatically inheriting events to child tasks, which enables process-wide events monitoring with low overheads. By default perf events are non-intrusive, not affecting behaviour of the tasks being monitored. For certain use-cases, however, it makes sense to leverage the generality of the perf events subsystem and optionally allow the tasks being monitored to receive signals on events they are interested in. This patch series adds the option to synchronously signal user space on events. To better support process-wide synchronous self-monitoring, without events propagating to children that do not share the current process's shared environment, two pre-requisite patches are added to optionally restrict inheritance to CLONE_THREAD, and remove events on exec (without affecting the parent). Examples how to use these features can be found in the two kselftests at the end of the series. The kselftests verify and stress test the basic functionality. The discussion at [1] led to the changes proposed in this series. The approach taken in patch "Add support for SIGTRAP on perf events" to use 'event_limit' to trigger the signal was kindly suggested by Peter Zijlstra in [2]. [1] https://lore.kernel.org/lkml/CACT4Y+YPrXGw+AtESxAgPyZ84TYkNZdP0xpocX2jwVAbZD=-XQ@mail.gmail.com/ [2] https://lore.kernel.org/lkml/YBv3rAT566k+6zjg@hirez.programming.kicks-ass.net/ Motivation and example uses: 1. Our immediate motivation is low-overhead sampling-based race detection for user space [3]. By using perf_event_open() at process initialization, we can create hardware breakpoint/watchpoint events that are propagated automatically to all threads in a process. As far as we are aware, today no existing kernel facility (such as ptrace) allows us to set up process-wide watchpoints with minimal overheads (that are comparable to mprotect() of whole pages). [3] https://llvm.org/devmtg/2020-09/slides/Morehouse-GWP-Tsan.pdf 2. Other low-overhead error detectors that rely on detecting accesses to certain memory locations or code, process-wide and also only in a specific set of subtasks or threads. Other ideas for use-cases we found interesting, but should only illustrate the range of potential to further motivate the utility (we're sure there are more): 3. Code hot patching without full stop-the-world. Specifically, by setting a code breakpoint to entry to the patched routine, then send signals to threads and check that they are not in the routine, but without stopping them further. If any of the threads will enter the routine, it will receive SIGTRAP and pause. 4. Safepoints without mprotect(). Some Java implementations use "load from a known memory location" as a safepoint. When threads need to be stopped, the page containing the location is mprotect()ed and threads get a signal. This could be replaced with a watchpoint, which does not require a whole page nor DTLB shootdowns. 5. Threads receiving signals on performance events to throttle/unthrottle themselves. 6. Tracking data flow globally. Signed-off-by: Peter Zijlstra (Intel) --- v2: * Patch "Support only inheriting events if cloned with CLONE_THREAD" added to series. * Patch "Add support for event removal on exec" added to series. * Patch "Add kselftest for process-wide sigtrap handling" added to series. * Patch "Add kselftest for remove_on_exec" added to series. * Implicitly restrict inheriting events if sigtrap, but the child was cloned with CLONE_CLEAR_SIGHAND, because it is not generally safe if the child cleared all signal handlers to continue sending SIGTRAP. * Various minor fixes (see details in patches). v1: https://lkml.kernel.org/r/20210223143426.2412737-1-elver@google.com Marco Elver (8): perf/core: Apply PERF_EVENT_IOC_MODIFY_ATTRIBUTES to children perf/core: Support only inheriting events if cloned with CLONE_THREAD perf/core: Add support for event removal on exec signal: Introduce TRAP_PERF si_code and si_perf to siginfo perf/core: Add support for SIGTRAP on perf events perf/core: Add breakpoint information to siginfo on SIGTRAP selftests/perf: Add kselftest for process-wide sigtrap handling selftests/perf: Add kselftest for remove_on_exec arch/m68k/kernel/signal.c | 3 + arch/x86/kernel/signal_compat.c | 5 +- fs/signalfd.c | 4 + include/linux/compat.h | 2 + include/linux/perf_event.h | 5 +- include/linux/signal.h | 1 + include/uapi/asm-generic/siginfo.h | 6 +- include/uapi/linux/perf_event.h | 5 +- include/uapi/linux/signalfd.h | 4 +- kernel/events/core.c | 130 ++++++++- kernel/fork.c | 2 +- kernel/signal.c | 11 + .../testing/selftests/perf_events/.gitignore | 3 + tools/testing/selftests/perf_events/Makefile | 6 + tools/testing/selftests/perf_events/config | 1 + .../selftests/perf_events/remove_on_exec.c | 256 ++++++++++++++++++ tools/testing/selftests/perf_events/settings | 1 + .../selftests/perf_events/sigtrap_threads.c | 202 ++++++++++++++ 18 files changed, 632 insertions(+), 15 deletions(-) create mode 100644 tools/testing/selftests/perf_events/.gitignore create mode 100644 tools/testing/selftests/perf_events/Makefile create mode 100644 tools/testing/selftests/perf_events/config create mode 100644 tools/testing/selftests/perf_events/remove_on_exec.c create mode 100644 tools/testing/selftests/perf_events/settings create mode 100644 tools/testing/selftests/perf_events/sigtrap_threads.c