Re: [RFC] dmaengine: pl330: fix a race condition in case of threaded irqs

[Jassi Brar]

On Mon, Dec 25, 2017 at 7:50 AM, Qi Hou <qi.hou@xxxxxxxxxxxxx> wrote:
> I found this problem below, and I now understand why it happens, but I'm not
>  100% sure what is the best way to fix it.
>
> When booting up with "threadirqs" in command line, all irq handlers of the DMA
> controller pl330 will be threaded forcedly. These threads will race for the same
> list, pl330->req_done.
>
> Before the callback, the spinlock was released. And after it, the spinlock was
> taken. This opened an race window where another threaded irq handler could steal
> the spinlock and be permitted to delete entries of the list, pl330->req_done.
>
The locking has been recently modified beyond recognition, so I can't
tell why that part of code is the way it is.
The safest and cleanest solution seems to be to not drop and re-aquire the lock.

Cheers!