Re: irq lock inversion

[Tejun Heo <tj@kernel.org>]

Hello, Ingo.

Ingo Molnar wrote:
> I havent looked deeply but at first sight i'm not 100% sure that even 
> the lock dance hack is safe - doesnt vfree() do TLB flushes, which must 
> be done with irqs enabled in general? If yes, then the whole notion of 
> using the allocator from irqs-off sections is wrong and the flags 
> save/restore is misguided (or at least incomplete).

The only place where any v*() call is nested under pcpu_lock is in the
alloc path, specifically pcpu_extend_area_map() ends up calling
vfree().  pcpu_free() path which can be called from irq context never
calls any vmalloc function directly.  The reclaiming is deferred to a
work.  Breaking the single nesting completely decouples the two locks
and nobody would be calling vfree() with irq disabled, so I don't
think there will be any problem.

Thanks.

-- 
tejun