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Tue, 13 Jul 2021 17:05:35 +0000 Received: from BL0PR12MB5506.namprd12.prod.outlook.com ([fe80::d017:af2f:7049:5482]) by BL0PR12MB5506.namprd12.prod.outlook.com ([fe80::d017:af2f:7049:5482%5]) with mapi id 15.20.4331.021; Tue, 13 Jul 2021 17:05:35 +0000 Date: Tue, 13 Jul 2021 14:05:33 -0300 From: Jason Gunthorpe To: Halil Pasic Cc: Tony Krowiak , linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, borntraeger@de.ibm.com, cohuck@redhat.com, pasic@linux.vnet.ibm.com, jjherne@linux.ibm.com, alex.williamson@redhat.com, kwankhede@nvidia.com, frankja@linux.ibm.com, david@redhat.com, imbrenda@linux.ibm.com, hca@linux.ibm.com Subject: Re: [PATCH] s390/vfio-ap: do not open code locks for VFIO_GROUP_NOTIFY_SET_KVM notification Message-ID: <20210713170533.GF136586@nvidia.com> References: <20210707154156.297139-1-akrowiak@linux.ibm.com> <20210713013815.57e8a8cb.pasic@linux.ibm.com> <5dd3cc05-f789-21a3-50c7-ee80d850a105@linux.ibm.com> <20210713184517.48eacee6.pasic@linux.ibm.com> Content-Type: text/plain; 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X-MS-Exchange-AntiSpam-MessageData-ChunkCount: 1 X-MS-Exchange-AntiSpam-MessageData-0: =?us-ascii?Q?sALT8+CLQ3miJ5AOuiVYxEf3ptjmfXvw8NoHIe8EmNNZdOCtv/o/xBLirlX3?= =?us-ascii?Q?rAQyD1/9TuOh46HmLUxhZv6/xVHjDnNXFsqgGPaosflEm2Shvk3nvYItFsJk?= =?us-ascii?Q?UkVNtM2p7i+x/AIIqbITJ8P923jYoKQe4xbJj7iOSIKWDveiPj6CPHvuEwTp?= =?us-ascii?Q?Vfz3d7b6hcJGxO+nq9hQsKA26mdgP7cTcKLsdjzsCpfFZ3QHn+RWvEw1+Qmg?= =?us-ascii?Q?+9K0a5b/QjwB69R1yuV2q+UaGmGDNU158x0li1j+jHXMlva8ybAo3PMAH1SU?= =?us-ascii?Q?1c2sPwZq0L3cbCcfJgB5/hq+lA9aK3P+pVo7YkhJk3A1qlcbU1TPHVZnZ7GW?= =?us-ascii?Q?OM3zg37YAzA+wvM9Zlj+p6aVVy2p8XFt3qno4fSpfWSNQIQwQUfk+EHs2frI?= =?us-ascii?Q?EP0c5svhjhfx+7VNiYpv6Ypyis03s6QR6SAgKZ0SFEFIUJSJjDBHmBL2/9d6?= =?us-ascii?Q?0HV3ZY0TeZtrbVUDG+vc8fYhU3QC4yZ8n5QM/TU0BVQgU9IgMj1p6189e4/2?= =?us-ascii?Q?BEgrEEkAFHwk9QMx6YPY76lbNqYn8MWcQ6+MwuL8raBlX6z3CP54JAABTV2/?= =?us-ascii?Q?7EQx/QDHNMI1zOdkRDw3l/95rOoduJk0wFEyN87NZcNf+nrh8m5kSRijsQBo?= =?us-ascii?Q?WgR0zIJB0gEYQzasOj6X4GcyxVPfo9FFnRMkuPSGGcsE4tq7Va66U7a5xPE8?= =?us-ascii?Q?iMDJuKViWQ5oPF2h7YPpKgMp8cQHLVIM6HZFv8U3dKaDIg1cojfRMIqAALdL?= =?us-ascii?Q?EH0jXaYh4c2YBaN4XViHiGRgDYZiu5czuDpYkDIAsqLlpNAKHYqPALbLKIR/?= =?us-ascii?Q?VKDgvB5V02y9W4LxxLj+kMOK9bUCrkz4PaEIVpJUKjw+qM19BSp8p01t3l4Y?= =?us-ascii?Q?tiO9NbfLWrSR88etF2QRmT/uFAJRbEER9NNkFlg5ALCEWbIDmw5D6KavP6qo?= =?us-ascii?Q?gSSF/SbxoFh53lbX7EZK8Url+0Ks4qDoTuC0EVHNfohRgJxXixvOHY5CHseI?= =?us-ascii?Q?jvhqNpH3yNt5SPRd6Te+Nx6eukiq4kwYYNLDd7lL4K+Z5Z1YbVbxUDpEGRgD?= =?us-ascii?Q?DxOyvLtKrCUTTLmSDUG6rI8Xe/B4+MtnQf5NhHZFRZxBsbLtBCeS0nax4DEi?= =?us-ascii?Q?QgCHkpd3C0rkpUq13k9K4YujGN7xOsHUbxMuihHn5dBWMn5QzQHHsGtAhPky?= =?us-ascii?Q?T/gzP11MhQhBxq4KG3S0csEcfrq67bhN/WYlP6wAdPd7MOqusxjNoLQKBO93?= =?us-ascii?Q?ZChcJHETXqrg5/g15dr+IahOdTNlks8XTL9n10vbE4yGX+xECc4sE5FthcH2?= =?us-ascii?Q?pYLKg8RC/1+QL99ZTcYMAGHa?= X-OriginatorOrg: Nvidia.com X-MS-Exchange-CrossTenant-Network-Message-Id: 4ba60883-7b29-41d8-5cbc-08d946206e0e X-MS-Exchange-CrossTenant-AuthSource: BL0PR12MB5506.namprd12.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-OriginalArrivalTime: 13 Jul 2021 17:05:35.0979 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 43083d15-7273-40c1-b7db-39efd9ccc17a X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: dV74SNqe8Bd4BGXGw9Q4PiHw8As0yagRlLi/pRxi1D1y0geu8D3iYYRvWrdP/98s X-MS-Exchange-Transport-CrossTenantHeadersStamped: BL1PR12MB5143 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jul 13, 2021 at 06:45:17PM +0200, Halil Pasic wrote: > Jason may give it another try to convince us that 0cc00c8d4050 only > silenced lockdep, but vfio_ap remained prone to deadlocks. To my best > knowledge using condition variable and a mutex is one of the well known > ways to implement an rwlock. The well known pattern is to use a rwsem. This: wait_event_cmd(matrix_mdev->wait_for_kvm, !matrix_mdev->kvm_busy, mutex_unlock(&matrix_dev->lock), mutex_lock(&matrix_dev->lock)); Is not really a rwsem, and is invsible to lockdep. Jason