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Fri, 15 May 2020 11:35:54 -0700 From: "Prakhya, Sai Praneeth" To: Joerg Roedel Subject: RE: [PATCH] iommu: Remove functions that support private domain Thread-Topic: [PATCH] iommu: Remove functions that support private domain Thread-Index: AQHWKXk9fV5tekATV0S4blj7EpvL1KioBUCA///Q9SCAAIhBgP//i0rwgACMGYD//71zcAAlw0mAAANT08A= Date: Fri, 15 May 2020 18:35:54 +0000 Message-ID: References: <20200513224721.20504-1-sai.praneeth.prakhya@intel.com> <20200514131315.GJ18353@8bytes.org> <20200514183233.GO18353@8bytes.org> <20200514195615.GP18353@8bytes.org> <20200515095919.GQ18353@8bytes.org> In-Reply-To: <20200515095919.GQ18353@8bytes.org> Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: dlp-product: dlpe-windows dlp-version: 11.2.0.6 dlp-reaction: no-action x-originating-ip: [10.22.254.140] MIME-Version: 1.0 Cc: "iommu@lists.linux-foundation.org" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" Hi Joerg, > -----Original Message----- > From: Joerg Roedel > Sent: Friday, May 15, 2020 2:59 AM > To: Prakhya, Sai Praneeth > Cc: iommu@lists.linux-foundation.org; Lu Baolu > Subject: Re: [PATCH] iommu: Remove functions that support private domain > > On Thu, May 14, 2020 at 11:12:52PM +0000, Prakhya, Sai Praneeth wrote: > > +static int is_driver_bound(struct device *dev, void *not_used) { > > + int ret = 0; > > + > > + device_lock(dev); > > + if (device_is_bound(dev)) > > + ret = 1; > > + device_unlock(dev); > > + return ret; > > +} > > This locks only one device, so without lock-conversion there could be a driver > probe after the device_unlock(), while we are probing the other devices of the > group. > > > [SNIP] > > > > + /* > > + * Check if any device in the group still has a driver binded to it. > > + * This might race with device driver probing code and unfortunately > > + * there is no clean way out of that either, locking all devices in the > > + * group and then do the re-attach will introduce a lock-inversion with > > + * group->mutex - Joerg. > > + */ > > + if (iommu_group_for_each_dev(group, NULL, is_driver_bound)) { > > + pr_err("Active drivers exist for devices in the group\n"); > > + return -EBUSY; > > + } > > The lock inversion comes into the picture when this code is called from > device(-driver) core through the bus-notifiers. The notifiers are called with the > device already locked. Make sense. I will look through that code. > > Another question I have is.. if it's racy then it should be racy even > > for one device iommu groups.. right? Why would it be racy only with > > multiple devices iommu group? > > Valid point. So the device needs to be locked _while_ the default domain change > happens. If triggered by sysfs there should be no locking problems, I guess. But > you better try it out. I will try this out and will update you. Regards, Sai _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu