Re: [PATCH] batman-adv: Broken sync while rescheduling delayed work

[Vlad Efanov]

Sven,


cancel_delayed_work_sync() and queue_delayed_work()

use WORK_STRUCT_PENDING_BIT in work->data to synchronize.

INIT_DELAYED_WORK() clears this bit.


The situation is :  __cancel_work_timer() sets WORK_STRUCT_PENDING_BIT

but INIT_DELAYED_WORK() in batadv_dat_start_timer() clears it

and queue_delayed_work() schedules new work.


Best regards,

Vlad.

On 26.05.2023 19:49, Sven Eckelmann wrote:
> On Friday, 26 May 2023 18:16:32 CEST Vladislav Efanov wrote:
> > The reason for these issues is the lack of synchronization. Delayed
> > work (batadv_dat_purge) schedules new timer/work while the device
> > is being deleted. As the result new timer/delayed work is set after
> > cancel_delayed_work_sync() was called. So after the device is freed
> > the timer list contains pointer to already freed memory.
> You are most likely right but could you please point out what in the worker is
> checked by the workqueue code that prevents it from being scheduled again?
> (and which seems to be overwritten as your patch seems to suggest)
>
> I think __cancel_work_timer marked the work as canceling but
> batadv_dat_start_timer reinitialized the worked (thus removing this important
> state). Would be nice if you could either correct me or confirm what I think to
> remember.
>
> Kind regards,
> 	Sven