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=-21.2 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 51B28C433E6 for ; Tue, 23 Feb 2021 14:35:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2323464DD3 for ; Tue, 23 Feb 2021 14:35:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232991AbhBWOf1 (ORCPT ); Tue, 23 Feb 2021 09:35:27 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58482 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232466AbhBWOf0 (ORCPT ); Tue, 23 Feb 2021 09:35:26 -0500 Received: from mail-qt1-x849.google.com (mail-qt1-x849.google.com [IPv6:2607:f8b0:4864:20::849]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E2867C061786 for ; Tue, 23 Feb 2021 06:34:45 -0800 (PST) Received: by mail-qt1-x849.google.com with SMTP id k28so10083794qtu.17 for ; Tue, 23 Feb 2021 06:34:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=sender:date:message-id:mime-version:subject:from:to:cc; bh=Q8hQJDMeUJlqSjrNYnPafLaJX5CJRNsJS+XYHF26pcU=; b=PJnNVGeDqB/jzzRFb43n6pABAUatJLV3VpoQVilcEqdrryJp08zjPufvVz5cFPnSEY t/li1aI0RjRwp7z2bUQbnWYCBL0UM2aSKop0ae9s2DpamNAajkWv+hxDEW2W9qIUp36d PAkr+ieLWes8nDdQ/+SEvLNzI2fhbLggfEVRl9YrCoom2ez47kSRP4/0+WUFn/kOA6Dt tTkwHtzevwds9t+smuh8yccupDpw+dh//SW88nsBdvQXbwTAsE8g1S7IxFZI03HwubvC rBVvVUVzattE0GWgZFrJETMXyA15a2rVhKdtnp2DazMEJEX4XDqEecySE72Fjn1RZ8Z0 L2rQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:date:message-id:mime-version:subject:from :to:cc; bh=Q8hQJDMeUJlqSjrNYnPafLaJX5CJRNsJS+XYHF26pcU=; b=VJwry7poyQZlfi4gkLjXIjA1/jtUECJ6opaqCsPkSgFlEJoRBPgTTs82IDw5iyYBVN OczqX4s8tsjNJv5gjbdb0gtrpmktT6//qpJNPVkMeHOU5+ZVT+LDHXQMxIfa9uyF3yTu ksaRljxsveT0ahd+tRU0Rq6QgWx0+3AHK1GwTOISRB4xz8iifaoA3sojaz82FZYZQDpn IA9zgMoMFrs+od5/v4ERjsxZjw1M35VMIFHat12OMm3A/Jb79JihozAQbjEkal2nQh2A yVrv2QT3Hu9vN1elKhBlCe6dKwLOXu9C6HLlz7lB+DWRo8q0JGVQBtu0pzETRv/13Eqv sZSQ== X-Gm-Message-State: AOAM532VWxKb6BUdU0S458aJL8rXiE6GZRD9IHaEejTOI+fY0eNu9C34 ZC6U2xvbufROLemzrU8TIrycCDh+jA== X-Google-Smtp-Source: ABdhPJwIekUA4sFfcyjccindFCcQp2ep8MthgqSzW3N3MtGLmm1PZlc40koEqgpP+XoOBcmnN/Qv1jzPlw== Sender: "elver via sendgmr" X-Received: from elver.muc.corp.google.com ([2a00:79e0:15:13:855b:f924:6e71:3d5d]) (user=elver job=sendgmr) by 2002:a0c:a8cf:: with SMTP id h15mr25576657qvc.20.1614090884790; Tue, 23 Feb 2021 06:34:44 -0800 (PST) Date: Tue, 23 Feb 2021 15:34:22 +0100 Message-Id: <20210223143426.2412737-1-elver@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.30.0.617.g56c4b15f3c-goog Subject: [PATCH RFC 0/4] 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, linux-m68k@lists.linux-m68k.org, x86@kernel.org Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@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. The discussion at [1] led to the changes proposed in this series. The approach taken in patch 3/4 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 example use-cases we found potentially interesting: 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 can be replaced with a watchpoint, which does not require a whole page nor DTLB shootdowns. 5. Tracking data flow globally. 6. Threads receiving signals on performance events to throttle/unthrottle themselves. Marco Elver (4): perf/core: Apply PERF_EVENT_IOC_MODIFY_ATTRIBUTES to children 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 arch/m68k/kernel/signal.c | 3 ++ arch/x86/kernel/signal_compat.c | 5 ++- fs/signalfd.c | 4 +++ include/linux/compat.h | 2 ++ include/linux/signal.h | 1 + include/uapi/asm-generic/siginfo.h | 6 +++- include/uapi/linux/perf_event.h | 3 +- include/uapi/linux/signalfd.h | 4 ++- kernel/events/core.c | 54 +++++++++++++++++++++++++++++- kernel/signal.c | 11 ++++++ 10 files changed, 88 insertions(+), 5 deletions(-) -- 2.30.0.617.g56c4b15f3c-goog