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([2a01:e0a:280:24f0:3f78:514a:4f03:fdc0]) by smtp.gmail.com with ESMTPSA id i2-20020adffc02000000b003364aa5cc13sm2859760wrr.1.2023.12.21.13.23.13 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 21 Dec 2023 13:23:13 -0800 (PST) Message-ID: Date: Thu, 21 Dec 2023 22:23:12 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PULL 20/47] backends/iommufd: Introduce the iommufd object Content-Language: en-US To: eric.auger@redhat.com, qemu-devel@nongnu.org Cc: Zhenzhong Duan , Peter Maydell , Richard Henderson , Nicholas Piggin , Harsh Prateek Bora , Thomas Huth , Eric Farman , Alex Williamson , Matthew Rosato , Yi Liu , Nicolin Chen References: <20231219185643.725448-1-clg@redhat.com> <20231219185643.725448-21-clg@redhat.com> From: =?UTF-8?Q?C=C3=A9dric_Le_Goater?= In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=clg@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.061, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 12/21/23 18:14, Eric Auger wrote: > Hi Cédric, > > On 12/21/23 17:00, Cédric Le Goater wrote: >> [ ... ] >> >> >>> +static void iommufd_backend_init(Object *obj) >>> +{ >>> +    IOMMUFDBackend *be = IOMMUFD_BACKEND(obj); >>> + >>> +    be->fd = -1; >>> +    be->users = 0; >>> +    be->owned = true; >>> +    qemu_mutex_init(&be->lock);> +} >>> + >>> +static void iommufd_backend_finalize(Object *obj) >>> +{ >>> +    IOMMUFDBackend *be = IOMMUFD_BACKEND(obj); >>> + >>> +    if (be->owned) { >>> +        close(be->fd); >>> +        be->fd = -1; >>> +    } >>> +} >>> + >>> +static void iommufd_backend_set_fd(Object *obj, const char *str, >>> Error **errp) >>> +{ >>> +    IOMMUFDBackend *be = IOMMUFD_BACKEND(obj); >>> +    int fd = -1; >>> + >>> +    fd = monitor_fd_param(monitor_cur(), str, errp); >>> +    if (fd == -1) { >>> +        error_prepend(errp, "Could not parse remote object fd %s:", >>> str); >>> +        return; >>> +    } >>> +    qemu_mutex_lock(&be->lock); >>> +    be->fd = fd; >>> +    be->owned = false; >>> +    qemu_mutex_unlock(&be->lock); >>> +    trace_iommu_backend_set_fd(be->fd); >>> +} >>> + >>> +static bool iommufd_backend_can_be_deleted(UserCreatable *uc) >>> +{ >>> +    IOMMUFDBackend *be = IOMMUFD_BACKEND(uc); >>> + >>> +    return !be->users; >> >> Coverity CID 1531549 reports a concurrent data access violation because >> be->users is being accessed without holding the mutex. >> >> I wonder how useful is this mutex anyhow, since the code paths should >> be protected by the BQL lock. If you agree, I will send an update to >> simply drop be->lock and solve this report. > I am not totally comfortable with the fact BQL covers the same > protection? Please can you elaborate. These routines are called when a device is created which is called from the QEMU main thread which exits holding the BQL. It should be fine. Thanks, C.