On Thu, Jul 27, 2023 at 12:23:08AM -0700, Nicolin Chen wrote: > The complication of the mutex and refcount will be amplified after we > introduce the replace support for access. So, add a preparatory change > of a constitutive helper iommufd_access_change_ioas(), to take care of > the existing iommufd_access_attach() and iommufd_access_detach(). > > Also, update the unprotect routine in iommufd_access_destroy_object() > to calling the new iommufd_access_change_ioas() helper. > > Suggested-by: Jason Gunthorpe <jgg@xxxxxxxxxx> > Signed-off-by: Nicolin Chen <nicolinc@xxxxxxxxxx> > --- > drivers/iommu/iommufd/device.c | 112 ++++++++++++++++++++------------- > 1 file changed, 69 insertions(+), 43 deletions(-) > > diff --git a/drivers/iommu/iommufd/device.c b/drivers/iommu/iommufd/device.c > index 7a3e8660b902..d9680a247e1c 100644 > --- a/drivers/iommu/iommufd/device.c > +++ b/drivers/iommu/iommufd/device.c > @@ -684,17 +684,69 @@ void iommufd_device_detach(struct iommufd_device *idev) > } > EXPORT_SYMBOL_NS_GPL(iommufd_device_detach, IOMMUFD); > > +static int iommufd_access_change_ioas(struct iommufd_access *access, > + struct iommufd_ioas *new_ioas) > +{ > + u32 iopt_access_list_id = access->iopt_access_list_id; > + struct iommufd_ioas *cur_ioas = access->ioas; > + int rc; > + > + lockdep_assert_held(&access->ioas_lock); > + > + /* We are racing with a concurrent detach, bail */ > + if (cur_ioas != access->ioas_unpin) > + return -EBUSY; > + > + if (IS_ERR(new_ioas)) > + return PTR_ERR(new_ioas); > + > + if (cur_ioas == new_ioas) { > + /* Do not forget to put since we allow a duplication */ > + iommufd_put_object(&new_ioas->obj); > + return 0; > + } > + > + /* > + * Set ioas to NULL to block any further iommufd_access_pin_pages(). > + * iommufd_access_unpin_pages() can continue using access->ioas_unpin. > + */ > + access->ioas = NULL; > + > + if (new_ioas) { > + rc = iopt_add_access(&new_ioas->iopt, access); > + if (rc) { > + iommufd_put_object(&new_ioas->obj); > + access->ioas = cur_ioas; > + return rc; > + } > + iommufd_ref_to_users(&new_ioas->obj); Kevin's suggestion to just open code the refcount_inc here And have a wrapper func that does: iommufd_access_change_ioas_id(struct iommufd_access *access, u32 id) { struct iommufd_ioas *ioas = iommufd_get_ioas(ictx, ioas_id); int rc; if (IS_ERR(ioas)) return PTR_ERR(ioas); rc = iommufd_access_change_ioas(access, ioas); iommufd_put_object(&ioas->obj); return rc; } Does looks cleaner Then we delete iommufd_ref_to_users() as there are no users (once all the branches are merged). Logic looks OK otherwise Jason