Re: [syzbot] possible deadlock in worker_thread

[Tetsuo Handa]

On 2022/02/12 3:59, Bart Van Assche wrote:
> On 2/10/22 11:27, syzbot wrote:
>> ======================================================
>> WARNING: possible circular locking dependency detected
>> 5.17.0-rc2-syzkaller-00398-gd8ad2ce873ab #0 Not tainted
>> ------------------------------------------------------
> 
> Since the SRP initiator driver is involved, I will take a look.
> However, I'm not sure yet when I will have the time to post a fix.
> 
> Thanks,
> 
> Bart.
> 

This problem was already handled by commit bf23747ee0532090 ("loop:
revert "make autoclear operation asynchronous"").

But this report might be suggesting us that we should consider
deprecating (and eventually getting rid of) system-wide workqueues
(declared in include/linux/workqueue.h), for since flush_workqueue()
synchronously waits for completion, sharing system-wide workqueues
among multiple modules can generate unexpected locking dependency
chain (like this report).

If some module needs flush_workqueue() or flush_*_work(), shouldn't
such module create and use their own workqueues?

Tejun, what do you think?