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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 5 Mar 2020 03:38:52 -0000 Received: from b06wcsmtp001.portsmouth.uk.ibm.com (b06wcsmtp001.portsmouth.uk.ibm.com [9.149.105.160]) by b06cxnps3074.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 0253cpG563176904 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 5 Mar 2020 03:38:51 GMT Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 587A0A405C; Thu, 5 Mar 2020 03:38:51 +0000 (GMT) Received: from b06wcsmtp001.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id B2436A405B; Thu, 5 Mar 2020 03:38:50 +0000 (GMT) Received: from ozlabs.au.ibm.com (unknown [9.192.253.14]) by b06wcsmtp001.portsmouth.uk.ibm.com (Postfix) with ESMTP; Thu, 5 Mar 2020 03:38:50 +0000 (GMT) Received: from adsilva.ozlabs.ibm.com (haven.au.ibm.com [9.192.254.114]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ozlabs.au.ibm.com (Postfix) with ESMTPSA id C64C2A0264; Thu, 5 Mar 2020 14:38:45 +1100 (AEDT) Subject: Re: [PATCH v3 16/27] powerpc/powernv/pmem: Register a character device for userspace to interact with From: "Alastair D'Silva" To: Frederic Barrat Cc: "Aneesh Kumar K . V" , "Oliver O'Halloran" , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman , Andrew Donnellan , Arnd Bergmann , Greg Kroah-Hartman , Dan Williams , Vishal Verma , Dave Jiang , Ira Weiny , Andrew Morton , Mauro Carvalho Chehab , "David S. Miller" , Rob Herring , Anton Blanchard , Krzysztof Kozlowski , Mahesh Salgaonkar , Madhavan Srinivasan , =?ISO-8859-1?Q?C=E9dric?= Le Goater , Anju T Sudhakar , Hari Bathini , Thomas Gleixner , Greg Kurz , Nicholas Piggin , Masahiro Yamada , Alexey Kardashevskiy , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, linux-nvdimm@lists.01.org, linux-mm@kvack.org Date: Thu, 05 Mar 2020 14:38:49 +1100 In-Reply-To: References: <20200221032720.33893-1-alastair@au1.ibm.com> <20200221032720.33893-17-alastair@au1.ibm.com> Organization: IBM Australia Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.34.4 (3.34.4-1.fc31) MIME-Version: 1.0 X-TM-AS-GCONF: 00 x-cbid: 20030503-0008-0000-0000-000003597306 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 20030503-0009-0000-0000-00004A7AA8AC Message-Id: <083251112829de95609c2220dde2e381940184cb.camel@au1.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.572 definitions=2020-03-04_10:2020-03-04,2020-03-04 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=2 adultscore=0 mlxscore=0 phishscore=0 impostorscore=0 lowpriorityscore=0 priorityscore=1501 mlxlogscore=999 clxscore=1015 malwarescore=0 spamscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2001150001 definitions=main-2003050017 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 2020-03-03 at 10:28 +0100, Frederic Barrat wrote: >=20 > Le 21/02/2020 =C3=A0 04:27, Alastair D'Silva a =C3=A9crit : > > From: Alastair D'Silva > >=20 > > This patch introduces a character device (/dev/ocxl-scmX) which > > further > > patches will use to interact with userspace. > >=20 > > Signed-off-by: Alastair D'Silva > > --- > > arch/powerpc/platforms/powernv/pmem/ocxl.c | 116 > > +++++++++++++++++- > > .../platforms/powernv/pmem/ocxl_internal.h | 2 + > > 2 files changed, 116 insertions(+), 2 deletions(-) > >=20 > > diff --git a/arch/powerpc/platforms/powernv/pmem/ocxl.c > > b/arch/powerpc/platforms/powernv/pmem/ocxl.c > > index b8bd7e703b19..63109a870d2c 100644 > > --- a/arch/powerpc/platforms/powernv/pmem/ocxl.c > > +++ b/arch/powerpc/platforms/powernv/pmem/ocxl.c > > @@ -10,6 +10,7 @@ > > #include > > #include > > #include > > +#include > > #include > > #include > > #include "ocxl_internal.h" > > @@ -339,6 +340,9 @@ static void free_ocxlpmem(struct ocxlpmem > > *ocxlpmem) > > =20 > > free_minor(ocxlpmem); > > =20 > > + if (ocxlpmem->cdev.owner) > > + cdev_del(&ocxlpmem->cdev); > > + > > if (ocxlpmem->metadata_addr) > > devm_memunmap(&ocxlpmem->dev, ocxlpmem->metadata_addr); > > =20 > > @@ -396,6 +400,70 @@ static int ocxlpmem_register(struct ocxlpmem > > *ocxlpmem) > > return device_register(&ocxlpmem->dev); > > } > > =20 > > +static void ocxlpmem_put(struct ocxlpmem *ocxlpmem) > > +{ > > + put_device(&ocxlpmem->dev); > > +} > > + > > +static struct ocxlpmem *ocxlpmem_get(struct ocxlpmem *ocxlpmem) > > +{ > > + return (get_device(&ocxlpmem->dev) =3D=3D NULL) ? NULL : ocxlpmem; > > +} > > + > > +static struct ocxlpmem *find_and_get_ocxlpmem(dev_t devno) > > +{ > > + struct ocxlpmem *ocxlpmem; > > + int minor =3D MINOR(devno); > > + /* > > + * We don't declare an RCU critical section here, as our AFU > > + * is protected by a reference counter on the device. By the > > time the > > + * minor number of a device is removed from the idr, the ref > > count of > > + * the device is already at 0, so no user API will access that > > AFU and > > + * this function can't return it. > > + */ >=20 > I fixed something related in the ocxl driver (which had enough > changes=20 > with the introduction of the "info" device to make a similar comment=20 > become wrong). See commit a58d37bce0d21. The issue is handling a=20 > simultaneous open() and removal of the device through /sysfs as best > we can. >=20 > We are on a file open path and it's not like we're going to have a=20 > thousand clients, so performance is not that critical. We can take > the=20 > mutex before searching in the IDR and release it after we increment > the=20 > reference count on the device. > But that's not enough: we could still find the device in the IDR > while=20 > it is being removed in free_ocxlpmem(). I believe the only safe way > to=20 > address it is by removing the user-facing APIs (the char device) > before=20 > calling device_unregister(). So that it's not possible to find the=20 > device in file_open() if it's in the middle of being removed. >=20 > Fred >=20 >=20 Ok, I'll replicate that patch & follow your advice. > > + ocxlpmem =3D idr_find(&minors_idr, minor); > > + if (ocxlpmem) > > + ocxlpmem_get(ocxlpmem); > > + return ocxlpmem; > > +} > > + > > +static int file_open(struct inode *inode, struct file *file) > > +{ > > + struct ocxlpmem *ocxlpmem; > > + > > + ocxlpmem =3D find_and_get_ocxlpmem(inode->i_rdev); > > + if (!ocxlpmem) > > + return -ENODEV; > > + > > + file->private_data =3D ocxlpmem; > > + return 0; > > +} > > + > > +static int file_release(struct inode *inode, struct file *file) > > +{ > > + struct ocxlpmem *ocxlpmem =3D file->private_data; > > + > > + ocxlpmem_put(ocxlpmem); > > + return 0; > > +} > > + > > +static const struct file_operations fops =3D { > > + .owner =3D THIS_MODULE, > > + .open =3D file_open, > > + .release =3D file_release, > > +}; > > + > > +/** > > + * create_cdev() - Create the chardev in /dev for the device > > + * @ocxlpmem: the SCM metadata > > + * Return: 0 on success, negative on failure > > + */ > > +static int create_cdev(struct ocxlpmem *ocxlpmem) > > +{ > > + cdev_init(&ocxlpmem->cdev, &fops); > > + return cdev_add(&ocxlpmem->cdev, ocxlpmem->dev.devt, 1); > > +} > > + > > /** > > * ocxlpmem_remove() - Free an OpenCAPI persistent memory device > > * @pdev: the PCI device information struct > > @@ -572,6 +640,11 @@ static int probe(struct pci_dev *pdev, const > > struct pci_device_id *ent) > > goto err; > > } > > =20 > > + if (create_cdev(ocxlpmem)) { > > + dev_err(&pdev->dev, "Could not create character > > device\n"); > > + goto err; > > + } >=20 > As already mentioned in a previous patch, we branch to the err label > so=20 > rc needs to be set to a valid error. >=20 Ok >=20 >=20 > > + > > elapsed =3D 0; > > timeout =3D ocxlpmem->readiness_timeout + ocxlpmem- > > >memory_available_timeout; > > while (!is_usable(ocxlpmem, false)) { > > @@ -613,20 +686,59 @@ static struct pci_driver pci_driver =3D { > > .shutdown =3D ocxlpmem_remove, > > }; > > =20 > > +static int file_init(void) > > +{ > > + int rc; > > + > > + mutex_init(&minors_idr_lock); > > + idr_init(&minors_idr); > > + > > + rc =3D alloc_chrdev_region(&ocxlpmem_dev, 0, NUM_MINORS, "ocxl- > > pmem"); > > + if (rc) { > > + idr_destroy(&minors_idr); > > + pr_err("Unable to allocate OpenCAPI persistent memory > > major number: %d\n", rc); > > + return rc; > > + } > > + > > + ocxlpmem_class =3D class_create(THIS_MODULE, "ocxl-pmem"); > > + if (IS_ERR(ocxlpmem_class)) { > > + idr_destroy(&minors_idr); > > + pr_err("Unable to create ocxl-pmem class\n"); > > + unregister_chrdev_region(ocxlpmem_dev, NUM_MINORS); > > + return PTR_ERR(ocxlpmem_class); > > + } > > + > > + return 0; > > +} > > + > > +static void file_exit(void) > > +{ > > + class_destroy(ocxlpmem_class); > > + unregister_chrdev_region(ocxlpmem_dev, NUM_MINORS); > > + idr_destroy(&minors_idr); > > +} > > + > > static int __init ocxlpmem_init(void) > > { > > - int rc =3D 0; > > + int rc; > > =20 > > - rc =3D pci_register_driver(&pci_driver); > > + rc =3D file_init(); > > if (rc) > > return rc; > > =20 > > + rc =3D pci_register_driver(&pci_driver); > > + if (rc) { > > + file_exit(); > > + return rc; > > + } > > + > > return 0; > > } > > =20 > > static void ocxlpmem_exit(void) > > { > > pci_unregister_driver(&pci_driver); > > + file_exit(); > > } > > =20 > > module_init(ocxlpmem_init); > > diff --git a/arch/powerpc/platforms/powernv/pmem/ocxl_internal.h > > b/arch/powerpc/platforms/powernv/pmem/ocxl_internal.h > > index 28e2020f6355..d2d81fec7bb1 100644 > > --- a/arch/powerpc/platforms/powernv/pmem/ocxl_internal.h > > +++ b/arch/powerpc/platforms/powernv/pmem/ocxl_internal.h > > @@ -2,6 +2,7 @@ > > // Copyright 2019 IBM Corp. > > =20 > > #include > > +#include > > #include > > #include > > #include > > @@ -99,6 +100,7 @@ struct ocxlpmem_function0 { > > struct ocxlpmem { > > struct device dev; > > struct pci_dev *pdev; > > + struct cdev cdev; > > struct ocxl_fn *ocxl_fn; > > struct nd_interleave_set nd_set; > > struct nvdimm_bus_descriptor bus_desc; > >=20 --=20 Alastair D'Silva Open Source Developer Linux Technology Centre, IBM Australia mob: 0423 762 819