spinlock deadlock

[Valdis.Kletnieks at vt.edu]

On Fri, 15 Feb 2013 17:17:38 +0530, anish singh said:
> adding Joe Perches  as generally he looks after printk stuff.
>
> On Fri, Feb 15, 2013 at 2:22 PM, buyitian <buyit at live.cn> wrote:
> > is it possible that printk cause deadlock? the path is as below:
> >
> > 1. taskA runs on CPU0, and run schedule to acqire the rq->lock.
> > 2. taskA calls printk while holding rq->lock.
> > 3. taskA holds console_sem.
> > 4. taskB runs on CPU1, and call console_lock(), which is blocked by
> > console_sem and queue itslef to the wait list.
> > 5. taskB migrates from CPU1 to cpu0. will this step occur?
> > 6. taskA calls up(&console_sem)-->
> > wake_up_process()-->try_to_wake_up()-->ttwu_queue()-->raw_spin_lock(&rq->lock).
> > here taskA tries to acquire the rq->lock of CPU0 again.

I'm not Joe, but what kernel release are you looking at?  ISTR that in
the last few releases (3.5-ish maybe?), that code got overhauled to
prevent a similar issue...
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