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 27073C6FD1C for ; Wed, 22 Mar 2023 14:15:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231201AbjCVOPz (ORCPT ); Wed, 22 Mar 2023 10:15:55 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47724 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231137AbjCVOPy (ORCPT ); Wed, 22 Mar 2023 10:15:54 -0400 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 50CB764864; Wed, 22 Mar 2023 07:15:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1679494541; x=1711030541; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=xQRrzlxhecTD5AMTnfLJZr21kEYVnBrnkCCGyzDt+j8=; b=IWfFU/G/PndH96tvTPaPN8+WqstvbzzbDwWQbOAy1lfmxA5Dnw43u/9o EbA0agS9kYbwf3F7yq6UFkxL4jxft9KasXImSWVEAR/WQy+ZVQjBxtPpN YF6+x8jsBzAeEwquFHDn+NKpuThWmdSPIPlH8VFGpzHoKGvyUOZzDihMd SOGdDlCPPNsJi5rTF4qeFNozZrZMou7/sLUYM73y2FLjPtGmt3Xh3TUY9 QC2E9GReUelVdWGQhywK4kE0wWQ4PM0keJwIoHTs0E3WUHSKAHqyrF+uH Q3/0VmHMWluPloeen03QL0cXI074CGvOidalA6Q7wxOc4+qbO+xj+RFDl g==; X-IronPort-AV: E=McAfee;i="6600,9927,10657"; a="340758720" X-IronPort-AV: E=Sophos;i="5.98,282,1673942400"; d="scan'208";a="340758720" Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Mar 2023 07:15:15 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=McAfee;i="6600,9927,10657"; a="927845152" X-IronPort-AV: E=Sophos;i="5.98,282,1673942400"; d="scan'208";a="927845152" Received: from ahunter6-mobl1.ger.corp.intel.com (HELO [10.0.2.15]) ([10.251.222.47]) by fmsmga006-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 22 Mar 2023 07:15:11 -0700 Message-ID: Date: Wed, 22 Mar 2023 16:15:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.9.0 Subject: Re: [PATCH] perf/core: Fix the same task check in perf_event_set_output Content-Language: en-US To: Peter Zijlstra , kan.liang@linux.intel.com Cc: alexander.shishkin@linux.intel.com, ak@linux.intel.com, nadav.amit@gmail.com, Zhengjun Xing , linux-kernel@vger.kernel.org, Arnaldo Carvalho de Melo , jolsa@kernel.org, Mark Rutland , mingo@redhat.com, Namhyung Kim , Ian Rogers , "linux-perf-users@vger.kernel.org" References: <20220711180706.3418612-1-kan.liang@linux.intel.com> <20230322134203.GB2357380@hirez.programming.kicks-ass.net> From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki In-Reply-To: <20230322134203.GB2357380@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On 22/03/23 15:42, Peter Zijlstra wrote: > On Wed, Mar 22, 2023 at 12:59:28PM +0200, Adrian Hunter wrote: >> On 11/07/22 21:07, kan.liang@linux.intel.com wrote: >>> From: Kan Liang >>> >>> With the --per-thread option, perf record errors out when sampling with >>> a hardware event and a software event as below. >>> >>> $ perf record -e cycles,dummy --per-thread ls >>> failed to mmap with 22 (Invalid argument) >>> >>> The same task is sampled with the two events. The IOC_OUTPUT is invoked >>> to share the mmap memory of the task between the events. In the >>> perf_event_set_output(), the event->ctx is used to check whether the >>> two events are attached to the same task. However, a hardware event and >>> a software event are from different task context. The check always >>> fails. >>> >>> The task struct is stored in the event->hw.target for each per-thread >>> event. It can be used to determine whether two events are attached to >>> the same task. >>> >>> The patch can also fix another issue reported months ago. >>> https://lore.kernel.org/all/92645262-D319-4068-9C44-2409EF44888E@gmail.com/ >>> The event->ctx is not ready when the perf_event_set_output() is invoked >>> in the perf_event_open(), while the event->hw.target has been assigned >>> at the moment. >>> >>> The problem should be a long time issue since commit c3f00c70276d >>> ("perf: Separate find_get_context() from event initialization"). The >>> event->hw.target doesn't exist at that time. Here, the patch which >>> introduces the event->hw.target is used by the Fixes tag. >>> >>> The problem should still exists between the broken patch and the >>> event->hw.target patch. This patch does not intend to fix that case. >>> >>> Fixes: 50f16a8bf9d7 ("perf: Remove type specific target pointers") >>> Reviewed-by: Zhengjun Xing >>> Signed-off-by: Kan Liang >> >> Did this slip through the cracks, or is there more complexity >> to this case than just sharing the rb? > > Both; I very much missed it, but looking at it now, I'm not at all sure > it is correct prior to the whole context rewrite we did recently. > > So after the rewrite every cpu/task only has a single > perf_event_context, and your change below is actually an equivalence. > > But prior to that a task could have multiple contexts. Now they got > co-scheduled most of the times and it will probably work, but I'm not > entirely sure. > > So how about we change the Fixes tag to something like: > > Fixes: c3f00c70276d ("perf: Separate find_get_context() from event initialization") # >= v6.2 > > And anybody that wants to back-port this further gets to either do the > full audit and/or keep the pieces. > > Hmm? Seems reasonable to me. Kan? > >>> --- >>> kernel/events/core.c | 2 +- >>> 1 file changed, 1 insertion(+), 1 deletion(-) >>> >>> diff --git a/kernel/events/core.c b/kernel/events/core.c >>> index b4d62210c3e5..22df79d3f19d 100644 >>> --- a/kernel/events/core.c >>> +++ b/kernel/events/core.c >>> @@ -12080,7 +12080,7 @@ perf_event_set_output(struct perf_event *event, struct perf_event *output_event) >>> /* >>> * If its not a per-cpu rb, it must be the same task. >>> */ >>> - if (output_event->cpu == -1 && output_event->ctx != event->ctx) >>> + if (output_event->cpu == -1 && output_event->hw.target != event->hw.target) >>> goto out; >>> >>> /* >>