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 AAEE3C83005 for ; Mon, 12 Jun 2023 12:18:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232678AbjFLMSJ (ORCPT ); Mon, 12 Jun 2023 08:18:09 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48798 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230335AbjFLMSI (ORCPT ); Mon, 12 Jun 2023 08:18:08 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8DDD78F; Mon, 12 Jun 2023 05:18:07 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 29F0C619AC; Mon, 12 Jun 2023 12:18:07 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id A0E37C433D2; Mon, 12 Jun 2023 12:18:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1686572286; bh=2+oPAHG4Lq6LModOSA2D8h8xmstG0BEfV6ZbR8S7Y8Y=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sj8wNPhQRZHzcIjWvoPlOsQz6EBp5D+0yuoBOBf83bH1hwRxLox4E7RGJhRk2NghN xa755zgQzSw+e2Yfys/knB0jTKwRMLTQ+b6wHVsmxOKPwgfsKV+aXY+NVX+QAZbIfh 7HHxW+YCm4bQuuayaxCSpDRkYiWs7euZm3ewUJfI= Date: Mon, 12 Jun 2023 14:18:03 +0200 From: Greg KH To: Peter Zijlstra Cc: torvalds@linux-foundation.org, keescook@chromium.org, pbonzini@redhat.com, masahiroy@kernel.org, nathan@kernel.org, ndesaulniers@google.com, nicolas@fjasle.eu, catalin.marinas@arm.com, will@kernel.org, vkoul@kernel.org, trix@redhat.com, ojeda@kernel.org, mingo@redhat.com, longman@redhat.com, boqun.feng@gmail.com, dennis@kernel.org, tj@kernel.org, cl@linux.com, acme@kernel.org, mark.rutland@arm.com, alexander.shishkin@linux.intel.com, jolsa@kernel.org, namhyung@kernel.org, irogers@google.com, adrian.hunter@intel.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, vschneid@redhat.com, paulmck@kernel.org, frederic@kernel.org, quic_neeraju@quicinc.com, joel@joelfernandes.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, rientjes@google.com, vbabka@suse.cz, roman.gushchin@linux.dev, 42.hyeyoo@gmail.com, apw@canonical.com, joe@perches.com, dwaipayanray1@gmail.com, lukas.bulwahn@gmail.com, john.johansen@canonical.com, paul@paul-moore.com, jmorris@namei.org, serge@hallyn.com, linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org, dmaengine@vger.kernel.org, llvm@lists.linux.dev, linux-perf-users@vger.kernel.org, rcu@vger.kernel.org, linux-security-module@vger.kernel.org, tglx@linutronix.de, ravi.bangoria@amd.com, error27@gmail.com, luc.vanoostenryck@gmail.com Subject: Re: [PATCH v3 46/57] perf: Simplify pmu_dev_alloc() Message-ID: <2023061213-knapsack-moonlike-e595@gregkh> References: <20230612090713.652690195@infradead.org> <20230612093540.850386350@infradead.org> <20230612094400.GG4253@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230612094400.GG4253@hirez.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org On Mon, Jun 12, 2023 at 11:44:00AM +0200, Peter Zijlstra wrote: > On Mon, Jun 12, 2023 at 11:07:59AM +0200, Peter Zijlstra wrote: > > > > Signed-off-by: Peter Zijlstra (Intel) > > --- > > kernel/events/core.c | 65 ++++++++++++++++++++++++--------------------------- > > 1 file changed, 31 insertions(+), 34 deletions(-) > > > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -11285,49 +11285,46 @@ static void pmu_dev_release(struct devic > > > > static int pmu_dev_alloc(struct pmu *pmu) > > { > > + int ret; > > > > + struct device *dev __free(put_device) = > > + kzalloc(sizeof(struct device), GFP_KERNEL); > > + if (!dev) > > + return -ENOMEM; > > > > + dev->groups = pmu->attr_groups; > > + device_initialize(dev); > > > > + dev_set_drvdata(dev, pmu); > > + dev->bus = &pmu_bus; > > + dev->release = pmu_dev_release; > > > > + ret = dev_set_name(dev, "%s", pmu->name); > > if (ret) > > + return ret; > > > > + ret = device_add(dev); > > if (ret) > > + return ret; > > > > + struct device *del __free(device_del) = dev; > > Greg, I'm not much familiar with the whole device model, but it seems > unfortunate to me that one has to call device_del() explicitly if we > already have a put_device() queued. > > Is there a saner way to write this? Ok, the "problem" here is that you have decided to do the "complex" way to initialize a struct device. And as such, you have to do more housekeeping than if you were to just use the simple interface. The rule is, after you call device_initialize() you HAVE to call put_device() on the pointer if something goes wrong and you want to clean up properly. Unless you have called device_add(), and at that point in time, then you HAVE to call device_del() if the device_add() call succeeded. If the device_add() call failed, then you HAVE to call put_device(). Yeah, it's a pain, but you are trying to hand-roll code that is not a "normal" path for a struct device, sorry. I don't know if you really can encode all of that crazy logic in the cleanup api, UNLESS you can "switch" the cleanup function at a point in time (i.e. after device_add() is successful). Is that possible? Anyway, let me see about just cleaning up this code in general, I don't think you need the complex interface here for a tiny struct device at all, which would make this specific instance moot :) Also, nit, you are racing with userspace by attempting to add new device files _AFTER_ the device is registered with the driver core, this whole thing can be made more simpler I hope, give me a bit... thanks greg k-h