From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 72E0D3F6C4D; Tue, 22 Sep 2026 13:44:59 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790084700; cv=none; b=DOXQ4rpekhcawl/t8E22CvSu7iBzsB+A64B28VFiQxMcD1ytJtIAebDYkufDCS4k4rIRh1d+XTgz9BTTOjq+x+JFFyOXt7XNECkK/incndoX+6QR2qFPegUV9y+MOI0JZYH9UNNbIp00K6OpqhVuhLLaEvZpzJQPdimaVowI+sw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1790084700; c=relaxed/simple; bh=Isi/XSz2XLB9elZLIuiT8+/gbeZBkYKpUNwCABDOIL8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=S4pZJoMXIyZ+mEbOnnPQNi3Xj9dSXmusNWnmKgG4VWQZTbj3/IdTzQZwj6GoRS190NPXJRmPcllmDqPvLrT17UT2Ge54uecO+6ENVKXbEGFAsZ9LyGA8+WAOEilIQNS/pNhE8m8r/WNMnrsTr96KSLFVYldRi0tOaodq7mG55hw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A6by66Bt; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="A6by66Bt" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4D71F1F00893; Tue, 22 Sep 2026 13:44:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1790084699; bh=tqTKHOB40XcCnMBIfF1XOtz8msytKJ8dl2VlRBxSVUo=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=A6by66Btcq0oxxz6XeUnbBptKL6e7P+vKxTSRd8BiR1vXllfVIL1v8yZ/52/UBbbY eAeuXgtI67QiZjmag3TyE6JzFmm1WtUJkI3YZDtBbo0+V8tEOaPK5+Y8peTNt3kKhn TDdNcW/gaZUQ8qZIviAfUdAVZ3OdT27z+5hPOts2aH/KSViaGseor1uECKJvjYAeTf Sel3yL7Z+cX6B+iQf31Cn/yYU+7u3hvoeQ2z0MXaQS8i5RxA9x3xq+dsfhWdVoCIat t321ThOK0x8hwvJ6weWtwpF0M/tMmQBWLDVzFcdub4xhDOyM7K5ICt0TKlC1n8oZy+ Bm9WFvk5XK+xA== Message-ID: Date: Tue, 22 Sep 2026 15:44:48 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v12 03/25] firmware: arm_scmi: Introduce protocol instance notifiers To: Cristian Marussi , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, arm-scmi@vger.kernel.org, linux-doc@vger.kernel.org Cc: sudeep.holla@kernel.org, james.quinlan@broadcom.com, f.fainelli@gmail.com, vincent.guittot@linaro.org, etienne.carriere@st.com, peng.fan@oss.nxp.com, michal.simek@amd.com, d-gole@ti.com, jic23@kernel.org, elif.topuz@arm.com, lukasz.luba@arm.com, philip.radford@arm.com, souvik.chakravarty@arm.com, leitao@kernel.org, kas@kernel.org, puranjay@kernel.org, usama.arif@linux.dev, kernel-team@meta.com, Jonathan Cameron References: <20260920091928.2014972-1-cristian.marussi@arm.com> <20260920091928.2014972-4-cristian.marussi@arm.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/20/26 11:19, Cristian Marussi wrote: > SCMI Protocol notifications are typically used by SCMI drivers to detect > and react to particular conditions: this was the assumption and the classic > usage scenario upon which the SCMI notification framework was built. Was the paragraph supposed to start with "SCMI notifications" ? Because later you describe how some protocols might want to reuse the "existing SCMI Notifications machinery", and here you talk about the traditional usage. > - mutex_lock(&info->protocols_mtx); > - pi = idr_find(&info->protocols, protocol_id); > + scoped_guard(mutex, &info->protocols_mtx) { > + pi = idr_find(&info->protocols, protocol_id); > + if (pi) { > + refcount_inc(&pi->users); > + } else { > + const struct scmi_protocol *proto; > > - if (pi) { > - refcount_inc(&pi->users); > - } else { > - const struct scmi_protocol *proto; > + /* Fails if protocol not registered on bus */ > + proto = scmi_protocol_get(protocol_id, &info->version); > + if (!proto) > + return ERR_PTR(-EPROBE_DEFER); > > - /* Fails if protocol not registered on bus */ > - proto = scmi_protocol_get(protocol_id, &info->version); > - if (proto) > pi = scmi_alloc_init_protocol_instance(info, proto); > - else > - pi = ERR_PTR(-EPROBE_DEFER); > + if (IS_ERR(pi)) > + return pi; > + > + proto_notifier_nb = READ_ONCE(pi->pno.nb); > + } > + } > + > + if (proto_notifier_nb) { > + if (scmi_protocol_notifier_register(pi->handle, &pi->pno)) > + dev_warn(handle->dev, > + "Failed to register protocol notifier\n"); if (proto_notifier_nb && scmi_protocol_notifier_register(pi->handle, &pi->pno)) dev_warn(handle->dev, ...) As we dropped the mutex, I assume somebody else could move ahead and refcount_inc(&pi->users) + return before the notifier was registered? Is that expected? > } > - mutex_unlock(&info->protocols_mtx); > > return pi; > } > @@ -2366,13 +2398,35 @@ int scmi_protocol_acquire(const struct scmi_handle *handle, u8 protocol_id) > void scmi_protocol_release(const struct scmi_handle *handle, u8 protocol_id) > { > struct scmi_info *info = handle_to_scmi_info(handle); > + struct notifier_block *proto_notifier_nb = NULL; > struct scmi_protocol_instance *pi; > > - mutex_lock(&info->protocols_mtx); > - pi = idr_find(&info->protocols, protocol_id); > - if (WARN_ON(!pi)) > - goto out; > + scoped_guard(mutex, &info->protocols_mtx) { > + pi = idr_find(&info->protocols, protocol_id); > + if (WARN_ON(!pi)) > + return; > > + /* > + * If a protocol notifier was registered and this is the > + * last istance releasing the protocol, mark the notifier s/istance/instance/ > + * for un-registration: note that the notifier itself counts > + * as one user, as for any other regular notification, so if a > + * protocol notifier is registered and there are only 2 users > + * active we can derive that this is the last protocol > + * instance de-registering. > + */ > + if (scmi_protocol_notifier_registered(&pi->pno) && > + refcount_read(&pi->users) == 2) > + proto_notifier_nb = READ_ONCE(pi->pno.nb); > + } > + We drop the mutex now temporarily. What happens if another instance gets registered (incrementing &pi->users) just after we dropped the lock and unregister the notifier? Shouldn't we care about that or why is it ok? -- Cheers, David