On Wed, 15 Apr 2020 08:08:24 +0200 Harald Freudenberger <freude@xxxxxxxxxxxxx> wrote: > On 14.04.20 14:58, Cornelia Huck wrote: > > On Tue, 7 Apr 2020 15:20:03 -0400 > > Tony Krowiak <akrowiak@xxxxxxxxxxxxx> wrote: > >> + /* The non-default driver's module must be loaded */ > >> + if (!try_module_get(drv->owner)) > >> + return 0; > > Is that really needed? I would have thought that the driver core's > > klist usage would make sure that the callback would not be invoked for > > drivers that are not registered anymore. Or am I missing a window? > The try_module_get() and module_put() is a result of review feedback from > my side. The ap bus core is static in the kernel whereas the > vfio dd is a kernel module. So there may be a race condition between > calling the callback function and removal of the vfio dd module. > There is similar code in zcrypt_api which does the same for the zcrypt > device drivers before using some variables or functions from the modules. > Help me, it this is outdated code and there is no need to adjust the > module reference counter any more, then I would be happy to remove > this code :-) I think the driver core already should keep us safe. A built-in bus calling a driver in a module is a very common pattern, and I think ->owner was introduced exactly for that case. Unless I'm really missing something obvious?
