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Tue, 05 Nov 2019 15:13:31 +0000 Received: from pps.filterd (aserp3030.oracle.com [127.0.0.1]) by aserp3030.oracle.com (8.16.0.27/8.16.0.27) with SMTP id xA5FB6tt027055; Tue, 5 Nov 2019 15:13:31 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3030.oracle.com with ESMTP id 2w35pp2pd1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 05 Nov 2019 15:13:30 +0000 Received: from abhmp0010.oracle.com (abhmp0010.oracle.com [141.146.116.16]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id xA5FDSHx018497; Tue, 5 Nov 2019 15:13:29 GMT Received: from bostrovs-us.us.oracle.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Tue, 05 Nov 2019 07:13:28 -0800 Subject: Re: [PATCH v2 09/15] xen/gntdev: use mmu_range_notifier_insert To: Jason Gunthorpe Cc: "linux-mm@kvack.org" , Jerome Glisse , Ralph Campbell , John Hubbard , "Felix.Kuehling@amd.com" , "linux-rdma@vger.kernel.org" , "dri-devel@lists.freedesktop.org" , "amd-gfx@lists.freedesktop.org" , Alex Deucher , Ben Skeggs , =?UTF-8?Q?Christian_K=c3=b6nig?= , David Zhou , Dennis Dalessandro , Juergen Gross , Mike Marciniszyn , Oleksandr Andrushchenko , Petr Cvek , Stefano Stabellini , "nouveau@lists.freedesktop.org" , "xen-devel@lists.xenproject.org" , Christoph Hellwig References: <20191028201032.6352-1-jgg@ziepe.ca> <20191028201032.6352-10-jgg@ziepe.ca> <3938b588-c6c5-3bd1-8ea9-47e4d5b2045c@oracle.com> <20191105023108.GN22766@mellanox.com> From: Boris Ostrovsky Autocrypt: addr=boris.ostrovsky@oracle.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: <20191105023108.GN22766@mellanox.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9432 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1911050126 X-Proofpoint-Virus-Version: vendor=nai engine=6000 definitions=9432 signatures=668685 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1908290000 definitions=main-1911050126 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 11/4/19 9:31 PM, Jason Gunthorpe wrote: > On Mon, Nov 04, 2019 at 05:03:31PM -0500, Boris Ostrovsky wrote: >> On 10/28/19 4:10 PM, Jason Gunthorpe wrote: >>> @@ -445,17 +438,9 @@ static void gntdev_vma_close(struct vm_area_stru= ct *vma) >>> struct gntdev_priv *priv =3D file->private_data; >>> =20 >>> pr_debug("gntdev_vma_close %p\n", vma); >>> - if (use_ptemod) { >>> - /* It is possible that an mmu notifier could be running >>> - * concurrently, so take priv->lock to ensure that the vma won't >>> - * vanishing during the unmap_grant_pages call, since we will >>> - * spin here until that completes. Such a concurrent call will >>> - * not do any unmapping, since that has been done prior to >>> - * closing the vma, but it may still iterate the unmap_ops list. >>> - */ >>> - mutex_lock(&priv->lock); >>> + if (use_ptemod && map->vma =3D=3D vma) { >> >> Is it possible for map->vma not to be equal to vma? > It could be NULL at least if use_ptemod is not set. > > Otherwise, I'm not sure, the confusing bit is that the map comes from > here: > > map =3D gntdev_find_map_index(priv, index, count); > > It looks like the intent is that the map->vma is always set to the > only vma that has the map as private_data. I am not sure how this can work otherwise. We stash map pointer in vm's vm_private_data and vice versa (for use_ptemod) gntdev_mmap() so if they have to match. That's why I was asking you to see if you had something particular in mind when you added this test. > So, I suppose it can be relaxed to a null test and a WARN_ON that it > hasn't changed? You mean if (use_ptemod) { =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 WARN_ON(map->vma !=3D vma); =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 ... Yes, that sounds good. -boris