spinlock deadlock

[buyitian]

I am looking at version 3.4

在 2013-2-16，0:17，Valdis.Kletnieks at vt.edu 写道：

> 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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