On Mon, Oct 24, 2022 at 05:22:24PM +0200, Niklas Schnelle wrote: > Thanks for the explanation, still would like to grok this a bit more if > you don't mind. If I do read things correctly synchronize_rcu() should > run in the conext of the VFIO ioctl in this case and shouldn't block > anything else in the kernel, correct? At least that's how I understand > the synchronize_rcu() comments and the fact that e.g. > net/vmw_vsock/virtio_transport.c:virtio_vsock_remove() also does a > synchronize_rcu() and can be triggered from user-space too. Yes, but I wouldn't look in the kernel to understand if things are OK > So we're > more worried about user-space getting slowed down rather than a Denial- > of-Service against other kernel tasks. Yes, functionally it is OK, but for something like vfio with vIOMMU you could be looking at several domains that have to be detached sequentially and with grace periods > 1s you can reach multiple seconds to complete something like a close() system call. Generally it should be weighed carefully Jason
