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

* 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
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