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=-6.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 BD0C9C4363A for ; Thu, 8 Oct 2020 13:15:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4561021897 for ; Thu, 8 Oct 2020 13:15:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="pKPbIDTD" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730199AbgJHNPk (ORCPT ); Thu, 8 Oct 2020 09:15:40 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45262 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725845AbgJHNPj (ORCPT ); Thu, 8 Oct 2020 09:15:39 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 83B4AC061755; Thu, 8 Oct 2020 06:15:39 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=JaQ+T90WKEsmTDN0IcV43yKJVPBOn1vkBHwJ2Y5Wb1o=; b=pKPbIDTDlUfvitahW5Nw+P5yuI nvNJGFIhol1qjRFQK/06ohMB6l7wf7S51vxszWhnedWVhYPN7FL//f7cBq4vU466aAZ255IHmjq3w 2aVgTyjAFE+AzazuilSHJwHQitz8XKZw4z7Ob+ip93by2hHgQC98EqbBfzG9ANIeyoH0JXIjWcii4 T9+Yn1NSF5jjrfcvibN/NwAMYbWSC0qSdJEjaSucImRoe20chjzmroyNP5or7ocgMcX6GSR8qeGAn EV24uMlgdzQIRoK4M8DHC3XAKbWY7rz9NAn3/ZtjDZcJ4ARwtBi+nc8/f5SVSx7GThoSU+niFBwWL rOBIzNcQ==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kQVlR-0008UV-Cb; Thu, 08 Oct 2020 13:15:21 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 3AA7B303A02; Thu, 8 Oct 2020 15:15:20 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2227F2B7801AD; Thu, 8 Oct 2020 15:15:20 +0200 (CEST) Date: Thu, 8 Oct 2020 15:15:20 +0200 From: Peter Zijlstra To: kajoljain Cc: acme@kernel.org, jolsa@redhat.com, linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org, maddy@linux.ibm.com, mingo@redhat.com, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, namhyung@kernel.org, daniel@iogearbox.net, brho@google.com, srikar@linux.vnet.ibm.com Subject: Re: [PATCH] perf/core: Fix hung issue on perf stat command during cpu hotplug Message-ID: <20201008131520.GY2628@hirez.programming.kicks-ass.net> References: <20200827064732.20860-1-kjain@linux.ibm.com> <931cf8fd-79e9-3cbd-0943-63abea31ee8d@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <931cf8fd-79e9-3cbd-0943-63abea31ee8d@linux.ibm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Oct 08, 2020 at 05:55:35PM +0530, kajoljain wrote: > > > On 8/27/20 12:17 PM, Kajol Jain wrote: > > Commit 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()") > > added assignment of ret value as -EAGAIN in case function > > call to 'smp_call_function_single' fails. > > For non-zero ret value, it did > > 'ret = !ret ? data.ret : -EAGAIN;', which always > > assign -EAGAIN to ret and make second if condition useless. > > > > In scenarios like when executing a perf stat with --per-thread option, and > > if any of the monitoring cpu goes offline, the 'smp_call_function_single' > > function could return -ENXIO, and with the above check, > > task_function_call hung and increases CPU > > usage (because of repeated 'smp_call_function_single()') > > > > Recration scenario: > > # perf stat -a --per-thread && (offline a CPU ) > > > > Patch here removes the tertiary condition added as part of that > > commit and added a check for NULL and -EAGAIN. > > Hi Peter, > Please let me know if you have any comment on this patch. Yes, sorry. I've got it now. Thanks! --- Subject: perf: Fix task_function_call() error handling From: Kajol Jain Date: Thu, 27 Aug 2020 12:17:32 +0530 From: Kajol Jain The error handling introduced by commit: 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()") looses any return value from smp_call_function_single() that is not {0, -EINVAL}. This is a problem because it will return -EXNIO when the target CPU is offline. Worse, in that case it'll turn into an infinite loop. Fixes: 2ed6edd33a21 ("perf: Add cond_resched() to task_function_call()") Reported-by: Srikar Dronamraju Signed-off-by: Kajol Jain Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Barret Rhoden Tested-by: Srikar Dronamraju Link: https://lkml.kernel.org/r/20200827064732.20860-1-kjain@linux.ibm.com --- kernel/events/core.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -99,7 +99,7 @@ static void remote_function(void *data) * retry due to any failures in smp_call_function_single(), such as if the * task_cpu() goes offline concurrently. * - * returns @func return value or -ESRCH when the process isn't running + * returns @func return value or -ESRCH or -ENXIO when the process isn't running */ static int task_function_call(struct task_struct *p, remote_function_f func, void *info) @@ -115,7 +115,8 @@ task_function_call(struct task_struct *p for (;;) { ret = smp_call_function_single(task_cpu(p), remote_function, &data, 1); - ret = !ret ? data.ret : -EAGAIN; + if (!ret) + ret = data.ret; if (ret != -EAGAIN) break;