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

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Date:   Tue, 21 Mar 2023 14:48:13 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Davidlohr Bueso <dave@...olabs.net>
CC:     <linux-cxl@...r.kernel.org>, <peterz@...radead.org>,
        <mingo@...hat.com>, <acme@...nel.org>, <mark.rutland@....com>,
        <will@...nel.org>, <dan.j.williams@...el.com>,
        <bwidawsk@...nel.org>, <ira.weiny@...el.com>,
        <vishal.l.verma@...el.com>, <alison.schofield@...el.com>,
        <linuxarm@...wei.com>, <linux-perf-users@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/4] cxl/pci: Find and register CXL PMU devices

On Mon, 6 Mar 2023 18:36:56 -0800
Davidlohr Bueso <dave@...olabs.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