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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3E299C433F5 for ; Fri, 24 Dec 2021 12:43:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352681AbhLXMkc (ORCPT ); Fri, 24 Dec 2021 07:40:32 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56312 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235763AbhLXMkb (ORCPT ); Fri, 24 Dec 2021 07:40:31 -0500 Received: from mail-pl1-x634.google.com (mail-pl1-x634.google.com [IPv6:2607:f8b0:4864:20::634]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DD98BC061757 for ; Fri, 24 Dec 2021 04:40:30 -0800 (PST) Received: by mail-pl1-x634.google.com with SMTP id u16so6574613plg.9 for ; Fri, 24 Dec 2021 04:40:30 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=vkaMjLSrWnNSKIxsm+YqOMH5aHbPwyhp0hWkPZSKCIM=; b=AFLAA49FbqsuxgvYmuClU8Ug7dP8wg4QG7O+nD14ujS4PrpIZ4BYnLuGWQhPnCDpro MN/M0ETWP6QAwG84M1fgN7t+W0OsQ5GMDctqZ72Fykw0PcvmW7hGihLfhHnhlL2qkiCg xCnL7vmimapkmiVeSq03ruraeO20I7jiN0Q215cvg+DxcJo2OPI3F3B0O6o/7LCXwzj+ 71NXALneYVs9kHFSxulLCuMqRJjJIbbyV7/9TSXy3RnkZY36pG7QDIh95Ugr0c/6ogVI wfRckqKUZP3SgySzYkDKc7lXJGxcIs5mNBwC+NrghGMr1FNxBOB9P8WO1A7HgFWh5tL+ Noag== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=vkaMjLSrWnNSKIxsm+YqOMH5aHbPwyhp0hWkPZSKCIM=; b=PKxEZmHqWcl+T94Y750m/AS92eFdPuPzLWoPPOT6guXa3UpwYLxd9z3l0nsVySlw9B +LgL1C3xoNwRZ2ZoMNJ1f5dG0Rw8SbdYrs1ygAVZFTUxHjT0xkltfQwyfDcqDz1fwO8j hbhwUIn6p4Joyv3bn5ycVr9V1oTih8uEL4KGPVAMGuggojZaTOKG03kDdrmVkAoR3zeI CZsGLy2LvmKvOMB32e7ijfvrm0e+Ndk54Ok7RlqjKPiPzi6bcfTTFCMREQ+wpexXMxMF 4EnqQ8Zk7BAtFgCmXChbs9qIVmZuoKqdAAIk8M+XbvkxZvfRIfFV5dSmQ/5701d7H+P7 uHjA== X-Gm-Message-State: AOAM530Ux05mD7uEahRNnMmDQXYKrp1KKY+N1Xy7febtZ7+t8h+xJFsF 2gAsV7FrvmDW811IM8Kod0MecA== X-Google-Smtp-Source: ABdhPJxD1s4hcy+HGU2tEEvPWtmHtypQXFYznV/whq4r6mO1x06m1jZP7wfkAm2Qe+QNr0w0W3RpdA== X-Received: by 2002:a17:902:b944:b0:148:be4b:66dd with SMTP id h4-20020a170902b94400b00148be4b66ddmr6358166pls.63.1640349629854; Fri, 24 Dec 2021 04:40:29 -0800 (PST) Received: from localhost ([134.195.101.46]) by smtp.gmail.com with ESMTPSA id k8sm7222685pjj.3.2021.12.24.04.40.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Dec 2021 04:40:29 -0800 (PST) From: Leo Yan To: Arnaldo Carvalho de Melo , Peter Zijlstra , Ingo Molnar , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Ian Rogers , linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Leo Yan Subject: [PATCH v1] perf synthetic-events: Return error if procfs isn't mounted for PID namespaces Date: Fri, 24 Dec 2021 20:40:13 +0800 Message-Id: <20211224124014.2492751-1-leo.yan@linaro.org> X-Mailer: git-send-email 2.25.1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org For perf recording, it retrieves process info by iterating nodes in proc fs. If we run perf in a non-root PID namespace with command: # unshare --fork --pid perf record -e cycles -a -- test_program ... in this case, unshare command creates a child PID namespace and launches perf tool in it, but the issue is the proc fs is not mounted for the non-root PID namespace, this leads to the perf tool gathering process info from its parent PID namespace. We can use below command to observe the process nodes under proc fs: # unshare --pid --fork ls /proc 1 137 1968 2128 3 342 48 62 78 crypto kcore net uptime 10 138 2 2142 30 35 49 63 8 devices keys pagetypeinfo version 11 139 20 2143 304 36 50 64 82 device-tree key-users partitions vmallocinfo 12 14 2011 22 305 37 51 65 83 diskstats kmsg self vmstat 128 140 2038 23 307 39 52 656 84 driver kpagecgroup slabinfo zoneinfo 129 15 2074 24 309 4 53 67 9 execdomains kpagecount softirqs 13 16 2094 241 31 40 54 68 asound fb kpageflags stat 130 164 2096 242 310 41 55 69 buddyinfo filesystems loadavg swaps 131 17 2098 25 317 42 56 70 bus fs locks sys 132 175 21 26 32 43 57 71 cgroups interrupts meminfo sysrq-trigger 133 179 2102 263 329 44 58 75 cmdline iomem misc sysvipc 134 1875 2103 27 330 45 59 76 config.gz ioports modules thread-self 135 19 2117 29 333 46 6 77 consoles irq mounts timer_list 136 1941 2121 298 34 47 60 773 cpuinfo kallsyms mtd tty So it shows many existed tasks, since unshared command has not mounted the proc fs for the new created PID namespace, it still accesses the proc fs of the root PID namespace. This leads to two prominent issues: - Firstly, PID values are mismatched between thread info and samples. The gathered thread info are coming from the proc fs of the root PID namespace, but samples record its PID from the child PID namespace. - The second issue is profiled program 'test_program' returns its forked PID number from the child PID namespace, perf tool wrongly uses this PID number to retrieve the process info via the proc fs of the root PID namespace. To avoid issues, we need to mount proc fs for the child PID namespace with the option '--mount-proc' when use unshare command: # unshare --fork --pid --mount-proc perf record -e cycles -a -- test_program Conversely, when the proc fs of the root PID namespace is used by child namespace, perf tool can detect the multiple PID levels and nsinfo__is_in_root_namespace() returns false, this patch reports error for this case: # unshare --fork --pid perf record -e cycles -a -- test_program Couldn't synthesize bpf events. Perf runs in non-root PID namespace but it tries to gather process info from its parent PID namespace. Please mount the proc file system properly, e.g. add the option '--mount-proc' for unshare command. Signed-off-by: Leo Yan --- tools/perf/util/synthetic-events.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/tools/perf/util/synthetic-events.c b/tools/perf/util/synthetic-events.c index 198982109f0f..cf7800347f77 100644 --- a/tools/perf/util/synthetic-events.c +++ b/tools/perf/util/synthetic-events.c @@ -1784,6 +1784,25 @@ int __machine__synthesize_threads(struct machine *machine, struct perf_tool *too perf_event__handler_t process, bool needs_mmap, bool data_mmap, unsigned int nr_threads_synthesize) { + /* + * When perf runs in non-root PID namespace, and the namespace's proc FS + * is not mounted, nsinfo__is_in_root_namespace() returns false. + * In this case, the proc FS is coming for the parent namespace, thus + * perf tool will wrongly gather process info from its parent PID + * namespace. + * + * To avoid the confusion that the perf tool runs in a child PID + * namespace but it synthesizes thread info from its parent PID + * namespace, returns failure with warning. + */ + if (!nsinfo__is_in_root_namespace()) { + pr_err("Perf runs in non-root PID namespace but it tries to "); + pr_err("gather process info from its parent PID namespace.\n"); + pr_err("Please mount the proc file system properly, e.g. "); + pr_err("add the option '--mount-proc' for unshare command.\n"); + return -EPERM; + } + if (target__has_task(target)) return perf_event__synthesize_thread_map(tool, threads, process, machine, needs_mmap, data_mmap); -- 2.25.1