Re: [BUG] usb: typec: ucsi: possible deadlock in ucsi_pr_swap() and ucsi_handle_connector_change()

[Heikki Krogerus]

 On Wed, Feb 09, 2022 at 11:50:57AM +0800, Jia-Ju Bai wrote:
> Hello,
> 
> My static analysis tool reports a possible deadlock in the ucsi driver in
> Linux 5.16:
> 
> ucsi_pr_swap()
>   mutex_lock(&con->lock); --> Line 962 (Lock A)
>   wait_for_completion_timeout(&con->complete, ...) --> Line 981 (Wait X)
> 
> ucsi_handle_connector_change()
>   mutex_lock(&con->lock); --> Line 763 (Lock A)
>   complete(&con->complete); --> Line 782 (Wake X)
>   complete(&con->complete); --> Line 807 (Wake X)
> 
> When ucsi_pr_swap() is executed, "Wait X" is performed by holding "Lock A".
> If ucsi_handle_connector_change() is executed at this time, "Wake X" cannot
> be performed to wake up "Wait X" in ucsi_handle_connector_change(), because
> "Lock A" has been already held by ucsi_handle_connector_change(), causing a
> possible deadlock.
> I find that "Wait X" is performed with a timeout, to relieve the possible
> deadlock; but I think this timeout can cause inefficient execution.
> 
> I am not quite sure whether this possible problem is real.
> Any feedback would be appreciated, thanks :)

This is probable a regression from commit ad74b8649bea ("usb: typec:
ucsi: Preliminary support for alternate modes"). Can you test does
this patch fix the issue (attached)?

thanks,

-- 
heikki