On Wed, 2017-03-08 at 10:17 -0700, Jason Gunthorpe wrote: > On Tue, Mar 07, 2017 at 11:12:43PM -0500, Hon Ching(Vicky) Lo wrote: > > On Mon, 2017-03-06 at 16:19 -0700, Jason Gunthorpe wrote: > > > > Also, how does locking work here? Does the vio core prevent > > > tpm_ibmvtpm_get_desired_dma and tpm_ibmvtpm_remove from running > > > concurrently? > > > > No, vio core doesn't prevent tpm_ibmvtpm_get_desired_dma and > > tpm_ibmvtpm_remove > > from running concurrently. > > > > vio_bus_probe calls vio_cmo_bus_probe which calls > > tpm_ibmvtpm_get_desired_dma. > > tpm_ibmvtpm_get_desired_dma is called before the code enters critical > > section. > > > > There is no locking mechanism around tpm_ibmvtpm_remove in vio_bus_remove. > > > > What's the concern here? > > tpm_ibmvtpm_remove makes the pointer that tpm_ibmvtpm_get_desired_dma > is accessing invalid, so some kind of locking is technically required > so that the two things do not create a use after free race: >
I don't think we need to worry about locking in this specific case. tpm_ibmvtpm_get_desired_dma was designed to return a default value in the case when the chip is not available. There is a locking mechanism between the probe and the remove at vio level. The 'get_desired_dma' is called before acquiring a lock within the probe code is rather a design than a bug. Vicky > > > + /* For tpm_ibmvtpm_get_desired_dma */ > > > + dev_set_drvdata(&vdev->dev, NULL); > > > kfree(ibmvtpm); > > Eg with the kfree above. > > It may be that the driver core prevents probe/remove from running > concurrently and things are fine, but this is something to confirm.. > > Jason >
