linux-kernel - Re: [PATCH v4 10/25] nvdimm: Add driver for OpenCAPI Persistent Memory

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Date:   Sat, 28 Mar 2020 19:59:46 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Alastair D'Silva <alastair@...ilva.org>
Cc:     "Aneesh Kumar K . V" <aneesh.kumar@...ux.ibm.com>,
        Oliver O'Halloran <oohall@...il.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Frederic Barrat <fbarrat@...ux.ibm.com>,
        Andrew Donnellan <ajd@...ux.ibm.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh@...nel.org>,
        Anton Blanchard <anton@...abs.org>,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Madhavan Srinivasan <maddy@...ux.vnet.ibm.com>,
        Cédric Le Goater <clg@...d.org>,
        Anju T Sudhakar <anju@...ux.vnet.ibm.com>,
        Hari Bathini <hbathini@...ux.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Greg Kurz <groug@...d.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Alexey Kardashevskiy <aik@...abs.ru>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-nvdimm@...ts.01.org, linux-mm@...ck.org
Subject: Re: [PATCH v4 10/25] nvdimm: Add driver for OpenCAPI Persistent
 Memory

On Sat, Mar 28, 2020 at 07:56:17PM -0700, Matthew Wilcox wrote:
> On Fri, Mar 27, 2020 at 06:11:47PM +1100, Alastair D'Silva wrote:
> > +static struct mutex minors_idr_lock;
> > +static struct idr minors_idr;
> ...
> > +	mutex_lock(&minors_idr_lock);
> > +	minor = idr_alloc(&minors_idr, ocxlpmem, 0, NUM_MINORS, GFP_KERNEL);
> > +	mutex_unlock(&minors_idr_lock);
> ...
> > +	mutex_lock(&minors_idr_lock);
> > +	idr_remove(&minors_idr, MINOR(ocxlpmem->dev.devt));
> > +	mutex_unlock(&minors_idr_lock);
> ...
> > +	mutex_init(&minors_idr_lock);
> > +	idr_init(&minors_idr);
> 
> Unless you look up ocxlpmem by minor number later in the patch series (and
> most of the series didn't make it to my mailbox), this can just be an ida.
> 
> static DEFINE_IDA(minors);
> ...
> minor = ida_alloc_max(&minors, NUM_MINORS, GFP_KERNEL);

Oops.  NUM_MINORS - 1.  Or #define MAX_MINOR 255 since you only seem to use
NUM_MINORS in this one place.

> ...
> ida_free(&minors, MINOR(ocxlpmem->dev.devt));
> ...
> and you can drop the dynamic initialisation.  And the mutex.