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 D21E1C4332F for ; Thu, 20 Oct 2022 13:46:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229928AbiJTNqK (ORCPT ); Thu, 20 Oct 2022 09:46:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57670 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229777AbiJTNqE (ORCPT ); Thu, 20 Oct 2022 09:46:04 -0400 Received: from mga03.intel.com (mga03.intel.com [134.134.136.65]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id A9747159A3C for ; Thu, 20 Oct 2022 06:45:52 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1666273560; x=1697809560; h=message-id:date:mime-version:subject:to:cc:references: from:in-reply-to:content-transfer-encoding; bh=sOvhO47D7FTpxIF0a2DwvTy4GmSSGRqIP8YnoXp6ofQ=; b=bhhyQR6pnTBFTGh26waGrzIrqekMuae2C6JdoiTwBncIm9szzlc3H7YN xMRXGr5bxXehotjBJt2BZJBH1kUfW++bY5ywbvzoXXuxMTtykMtNB2tuW 1RSs9sRARmn8CSlsrFZXhFop4SNnCTNSWu8Q7cdzP9oQ/yZ23VFqxwhRH UxDDIJ/LvLpSvyRMErz5aYdLOSB0+/+AWzV3eKI+DIqToOE6hRm2OVeAV MefP3uNH/MYT/367QpkcikejgyT4jjKDSFC5frY+l1GrgATfXqykDpp7i V+O3GO4c3KLEFBmHm2Q2yp5UdpnSltlZAl0kIYhx5IEG0ccKDs+cotG4z A==; X-IronPort-AV: E=McAfee;i="6500,9779,10506"; a="308390701" X-IronPort-AV: E=Sophos;i="5.95,198,1661842800"; d="scan'208";a="308390701" Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga103.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Oct 2022 06:45:52 -0700 X-IronPort-AV: E=McAfee;i="6500,9779,10506"; a="692990171" X-IronPort-AV: E=Sophos;i="5.95,198,1661842800"; d="scan'208";a="692990171" Received: from aasthash-mobl.ger.corp.intel.com (HELO [10.213.232.117]) ([10.213.232.117]) by fmsmga008-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 20 Oct 2022 06:45:51 -0700 Message-ID: Date: Thu, 20 Oct 2022 14:45:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.3.2 Subject: Re: [Intel-gfx] signal: break out of wait loops on kthread_stop() Content-Language: en-US To: "Jason A. Donenfeld" Cc: "Intel-gfx@lists.freedesktop.org" , "Eric W. Biederman" , linux-kernel@vger.kernel.org, sultan@kerneltoast.com References: <0029af41-bf24-9972-10ac-f52e1bdcbf08@linux.intel.com> <41455798-1dcb-135f-516d-25ab9a8082f5@linux.intel.com> <8acc3e4a-abbc-32bc-626e-7a216f6755c3@linux.intel.com> From: Tvrtko Ursulin Organization: Intel Corporation UK Plc In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/10/2022 21:19, Jason A. Donenfeld wrote: > On Wed, Oct 19, 2022 at 09:09:28PM +0100, Tvrtko Ursulin wrote: >> Hm why is kthread_stop() after kthread_run() abuse? I don't see it in >> kerneldoc that it must not be used for stopping threads. > > Because you don't want it to stop. You want to wait until it's done. If > you call stop right after run, it will even stop it before it even > begins to run. That's why you wind up sprinkling your msleeps > everywhere, indicating that clearly this is not meant to work that way. Not after kthread_run which wakes it up already. If the kerneldoc for kthread_stop() is correct at least... In which case I really do think that the yields are pointless/red herring. Perhaps they predate kthread_run and then they were even wrong. >> Yep the yields and sleeps are horrible and will go. But they are also >> not relevant for the topic at hand. > > Except they very much are. The reason you need these is because you're > using kthread_stop() for something it's not meant to do. It is supposed to assert kthread_should_stop() which thread can look at as when to exit. Except that now it can fail to get to that controlled exit point. Granted that argument is moot since it implies incomplete error handling in the thread anyway. Btw there are actually two use cases in our code base. One is thread controls the exit, second is caller controls the exit. Anyway... >> Never mind, I was not looking for anything more than a suggestion on how >> to maybe work around it in piece as someone is dealing with the affected >> call sites. > > Sultan's kthread_work idea is probably the right direction. This would > seem to have what you need. ... yes, it can be converted. Even though for one of the two use cases we need explicit signalling. There now isn't anything which would assert kthread_should_stop() without also asserting the signal, right?. Neither I found that the thread work API can do it. Fingers crossed we were the only "abusers" of the API. There's a quite a number of kthread_stop callers and it would be a large job to audit them all. Regards, Tvrtko