Messages in this thread | | | Date | Mon, 14 Feb 2022 10:08:00 +0900 | Subject | Re: [syzbot] possible deadlock in worker_thread | From | Tetsuo Handa <> |
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On 2022/02/14 8:06, Bart Van Assche wrote: > On 2/12/22 09:14, Tetsuo Handa wrote: >> How can reviewing all flush_workqueue(system_long_wq) calls help? > > It is allowed to queue blocking actions on system_long_wq.
Correct.
> flush_workqueue(system_long_wq) can make a lower layer (e.g. ib_srp) > wait on a blocking action from a higher layer (e.g. the loop driver) > and thereby cause a deadlock.
Correct.
> Hence my proposal to review all flush_workqueue(system_long_wq) calls.
Maybe I'm misunderstanding what the "review" means.
My proposal is to "rewrite" any module which needs to call flush_workqueue() on system-wide workqueues or call flush_work()/flush_*_work() which will depend on system-wide workqueues.
That is, for example, "rewrite" ib_srp module not to call flush_workqueue(system_long_wq).
+ srp_tl_err_wq = alloc_workqueue("srp_tl_err_wq", 0, 0);
- queue_work(system_long_wq, &target->tl_err_work); + queue_work(srp_tl_err_wq, &target->tl_err_work);
- flush_workqueue(system_long_wq); + flush_workqueue(srp_tl_err_wq);
+ destroy_workqueue(srp_tl_err_wq);
Then, we can call WARN_ON() if e.g. flush_workqueue() is called on system-wide workqueues.
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