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[34.168.104.7]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-30a3471ee7esm2100393a91.4.2025.04.30.12.57.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 30 Apr 2025 12:57:01 -0700 (PDT) Date: Wed, 30 Apr 2025 12:56:57 -0700 From: William McVicker To: Robin Murphy Cc: joro@8bytes.org, will@kernel.org, Bjorn Helgaas , iommu@lists.linux.dev, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org Subject: Re: [PATCH] PCI: Fix driver_managed_dma check Message-ID: References: <20250425133929.646493-4-robin.murphy@arm.com> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250425133929.646493-4-robin.murphy@arm.com> On 04/25/2025, Robin Murphy wrote: > Since it's not currently safe to take device_lock() in the IOMMU probe > path, that can race against really_probe() setting dev->driver before > attempting to bind. The race itself isn't so bad, since we're only > concerned with dereferencing dev->driver itself anyway, but sadly my > attempt to implement the check with minimal churn leads to a kind of > TOCTOU issue, where dev->driver becomes valid after to_pci_driver(NULL) > is already computed, and thus the check fails to work as intended. > > Will and I both hit this with the platform bus, but the pattern here is > the same, so fix it for correctness too. Thanks! Reviewed-by: Will McVicker > > Reported-by: Will McVicker > Fixes: bcb81ac6ae3c ("iommu: Get DT/ACPI parsing into the proper probe path") > Signed-off-by: Robin Murphy > --- > drivers/pci/pci-driver.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/pci/pci-driver.c b/drivers/pci/pci-driver.c > index c8bd71a739f7..66e3bea7dc1a 100644 > --- a/drivers/pci/pci-driver.c > +++ b/drivers/pci/pci-driver.c > @@ -1634,7 +1634,7 @@ static int pci_bus_num_vf(struct device *dev) > */ > static int pci_dma_configure(struct device *dev) > { > - struct pci_driver *driver = to_pci_driver(dev->driver); > + const struct device_driver *drv = READ_ONCE(dev->driver); > struct device *bridge; > int ret = 0; > > @@ -1651,8 +1651,8 @@ static int pci_dma_configure(struct device *dev) > > pci_put_host_bridge_device(bridge); > > - /* @driver may not be valid when we're called from the IOMMU layer */ > - if (!ret && dev->driver && !driver->driver_managed_dma) { > + /* @drv may not be valid when we're called from the IOMMU layer */ > + if (!ret && drv && !to_pci_driver(drv)->driver_managed_dma) { > ret = iommu_device_use_default_domain(dev); > if (ret) > arch_teardown_dma_ops(dev); > -- > 2.39.2.101.g768bb238c484.dirty >