Re: [PATCHv2] thunderbolt: do not double dequeue a request
From: Mika Westerberg
Date: Thu Mar 27 2025 - 10:22:14 EST
Hi,
On Thu, Mar 27, 2025 at 11:02:04PM +0900, Sergey Senozhatsky wrote:
> Hi,
>
> On (25/03/27 15:37), Mika Westerberg wrote:
> > > Another possibility can be tb_cfg_request_sync():
> > >
> > > tb_cfg_request_sync()
> > > tb_cfg_request()
> > > schedule_work(&req->work) -> tb_cfg_request_dequeue()
> > > tb_cfg_request_cancel()
> > > schedule_work(&req->work) -> tb_cfg_request_dequeue()
> >
> > Not sure about this one because &req->work will only be scheduled once the
> > second schedule_work() should not queue it again (as far as I can tell).
>
> If the second schedule_work() happens after a timeout, that's what
> !wait_for_completion_timeout() does, then the first schedule_work()
> can already execute the work by that time, and then we can schedule
> the work again (but the request is already dequeued). Am I missing
> something?
schedule_work() does not schedule the work again if it is already
scheduled.
> > > To address the issue, do not dequeue requests that don't
> > > have TB_CFG_REQUEST_ACTIVE bit set.
> >
> > Just to be sure. After this change you have not seen the issue anymore
> > with your testing?
>
> Haven't tried it yet.
>
> We just found it today, it usually takes several weeks before
> we can roll out the fix to our fleet and we prefer patches from
> upstream/subsystem git, so that's why we reach out to the upstream.
Makes sense.
> The 0xdead000000000122 deference is a LIST_POISON on x86_64, which
> is set explicitly in list_del(), so I'd say I'm fairly confident
> that we have a double list_del() in tb_cfg_request_dequeue().
Yes, I agree but since I have not seen any similar reports (sans what I saw
ages ago), I would like to be sure the issue you see is actually fixed with
the patch (and that there are no unexpected side-effects). ;-)