On Wed, Oct 17, 2018 at 06:22:48PM -0700, Andy Lutomirski wrote: > > > On Oct 17, 2018, at 5:54 PM, Nadav Amit <na...@vmware.com> wrote: > > > > It is sometimes beneficial to prevent preemption for very few > > instructions, or prevent preemption for some instructions that precede > > a branch (this latter case will be introduced in the next patches). > > > > To provide such functionality on x86-64, we use an empty REX-prefix > > (opcode 0x40) as an indication that preemption is disabled for the > > following instruction. > > Nifty! > > That being said, I think you have a few bugs.
> First, you can’t just ignore a rescheduling interrupt, as you > introduce unbounded latency when this happens — you’re effectively > emulating preempt_enable_no_resched(), which is not a drop-in > replacement for preempt_enable(). > To fix this, you may need to jump to a slow-path trampoline that calls > schedule() at the end or consider rewinding one instruction instead. > Or use TF, which is only a little bit terrifying... At which point we're very close to in-kernel rseq.
