On Fri, 2017-08-25 at 21:03 +0300, Michael S. Tsirkin wrote: > On Wed, Aug 16, 2017 at 10:36:47AM -0700, Eric Dumazet wrote: > > From: Eric Dumazet <eduma...@google.com> > > > > As found by syzkaller, malicious users can set whatever tx_queue_len > > on a tun device and eventually crash the kernel. > > > > Lets remove the ALIGN(XXX, SMP_CACHE_BYTES) thing since a small > > ring buffer is not fast anyway. > > I'm not sure it's worth changing for small rings. > > Does kmalloc_array guarantee cache line alignment for big buffers > then? If the ring is misaligned it will likely cause false sharing > as it's designed to be accessed from two CPUs.
I specifically said that in the changelog : "since a small ring buffer is not fast anyway." If one user sets up a pathological small ring buffer, kernel should not try to fix it. In this case, you would have to setup a ring of 2 or 4 slots to eventually hit false sharing.
