arch, mm: Remove tlb_fast_mode()

arch, mm: Remove tlb_fast_mode()

Since the introduction of preemptible mmu_gather TLB fast mode has been
broken. TLB fast mode relies on there being absolutely no concurrency;
it frees pages first and invalidates TLBs later.

However now we can get concurrency and stuff goes *bang*.

This patch removes all tlb_fast_mode() code; it was found the better
option vs trying to patch the hole by entangling tlb invalidation with
the scheduler.

Cc: Thomas Gleixner <[email protected]>
Cc: Russell King <[email protected]>
Cc: Tony Luck <[email protected]>
Reported-by: Max Filippov <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>