Re: CFQ + 2.6.13-rc4-RT-V0.7.52-02 = BUG: scheduling with irqs disabled

[Ingo Molnar <mingo@elte.hu>]

* Jens Axboe <axboe@suse.de> wrote:

> There can quite easily be lots of pending IO for the io_context (and, 
> in CFQ's case, below cfq_io_contexts), task exiting is completely 
> decoupled from any pending io.

yes, but that only affects the io_context reference count. Actual new 
use of tsk->io_context should only be possible on the IO-submission 
side, which should all have stopped by the time we execute do_exit().  
(and it's synchronous anyway, so the fact that we are executing in the 
kernel prevents the same thread from submitting new IO, in this case.)

i.e. the removal of tsk->io_context can be done without locking out 
interrupts. No interrupt or io_context is supposed to access 
current->io_context at that point.

> Then there's the cfq_exit_io_context() locking. I have to ponder this 
> a bit, I cannot even convince myself that it is currently safe right 
> now.

i think it should be mostly safe already - it seems to be overlocking a 
bit. E.g. the read_lock_irq(&tasklist_lock) could be a simple 
read_lock() i think.

	Ingo