On Tue, 17 Oct 2023 10:42:46 +0300 Ido Schimmel wrote: > Like other buses, devices on the netdevsim bus have a release callback > that is invoked when the reference count of the device drops to zero. > However, unlike other buses such as PCI, the release callback is not > necessarily built into the kernel, as netdevsim can be built as a > module. > > This above is problematic as nothing prevents the module from being > unloaded before the release callback has been invoked, which can happen > asynchronously. One such example is going to be added in subsequent > patches where devlink will call put_device() from an RCU callback. > > The issue is not theoretical and the reproducer in [1] can reliably > crash the kernel. The conclusion of this discussion was that the issue > should be solved in netdevsim, which is what this patch is trying to do. > > Add a reference count that is increased when a device is added to the > bus and decreased when a device is released. Signal a completion when > the reference count drops to zero and wait for the completion when > unloading the module so that the module will not be unloaded before all > the devices were released. The reference count is initialized to one so > that completion is only signaled when unloading the module. > > With this patch, the reproducer in [1] no longer crashes the kernel. > > [1] https://lore.kernel.org/netdev/20230619125015.1541143-2-idosch@xxxxxxxxxx/ > > Signed-off-by: Ido Schimmel <idosch@xxxxxxxxxx> Reviewed-by: Jakub Kicinski <kuba@xxxxxxxxxx>
