Re: [PATCH 2/4] cxl/pci: Find and register CXL PMU devices

From: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
To: Davidlohr Bueso <dave@stgolabs.net>
Cc: <linux-cxl@vger.kernel.org>, <peterz@infradead.org>,
	<mingo@redhat.com>, <acme@kernel.org>, <mark.rutland@arm.com>,
	<will@kernel.org>, <dan.j.williams@intel.com>,
	<bwidawsk@kernel.org>, <ira.weiny@intel.com>,
	<vishal.l.verma@intel.com>, <alison.schofield@intel.com>,
	<linuxarm@huawei.com>, <linux-perf-users@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 2/4] cxl/pci: Find and register CXL PMU devices
Date: Tue, 21 Mar 2023 14:48:13 +0000	[thread overview]
Message-ID: <20230321144813.00002c19@Huawei.com> (raw)
In-Reply-To: <20230307023656.cyntxctzqgpam5u3@offworld>

On Mon, 6 Mar 2023 18:36:56 -0800
Davidlohr Bueso <dave@stgolabs.net> wrote:

> On Fri, 03 Mar 2023, Jonathan Cameron wrote:
> 
> >+int devm_cxl_cpmu_add(struct device *parent, struct cxl_cpmu_regs *regs, int index)
> >+{
> >+	struct cxl_cpmu *cpmu;
> >+	struct device *dev;
> >+	int rc;
> >+
> >+	cpmu = kzalloc(sizeof(*cpmu), GFP_KERNEL);
> >+	if (!cpmu)
> >+		return -ENOMEM;
> >+
> >+	cpmu->base = regs->cpmu;
> >+	dev = &cpmu->dev;
> >+	device_initialize(dev);
> >+	device_set_pm_not_required(dev);
> >+	dev->parent = parent;
> >+	dev->bus = &cxl_bus_type;
> >+	dev->type = &cxl_cpmu_type;
> >+	rc = ida_alloc(&cpmu_ida, GFP_KERNEL);
> >+	if (rc < 0)
> >+		goto err;  
> 
> Probably better to do the ida_alloc after the cpmu allocation above, before
> arming the dev.

Hi Davidlohr,

There was a bug hiding here I think as the device_put() could cause the ida
to be freed even though the ida_alloc() failed.

Good you pointed out this oddity.

Moving the ida_alloc earlier requires an explicit free of the cpmu
but that's easy enough to locally to that if (rc < 0)

Thanks,

Jonathan