switch_mm race condition with Ingo's scheduler

Hi,

I found another race condition with the O(1) MQ scheduler from Ingo. The pattern is the following:

CPU#0:
------
schedule -> take runqueue #0 lock
context_switch
activate_mm
get_new_mmu_context
wrap_mmu_context
flush_tlb_all
smp_call_function (and wait...)

CPU#1:
------
schedule -> disable interrupts, take runqueue #1 lock
load_balance -> wants to get task from runqueue #0: release rq#1,
spinlock on rq #0 (interrupts disabled) => wait forever...

As the interrupts are disabled on CPU#1, the IPI cannot reach CPU#1.

Enabling interrupts while waiting for the rq#0 lock in load_balance is not an option because it leads to other race conditions (the timer-interrupt may call sched_tick and load_balance and end up spin-waiting on the same lock).

Is it really necessary to flush all TLBs when doing a context switch on one?

Any ideas, solutions?

Thanks,
Erich