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Message-ID: <1355423836.9463.14.camel@jlt4.sipsolutions.net> (sfid-20121213_193655_769037_826EEAE5)
Subject: Re: Add a new work-queue for destructing stations?
From: Johannes Berg <johannes@sipsolutions.net>
To: Ben Greear <greearb@candelatech.com>
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Date: Thu, 13 Dec 2012 19:37:16 +0100
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On Thu, 2012-12-13 at 10:30 -0800, Ben Greear wrote:
> On 12/13/2012 10:24 AM, Johannes Berg wrote:
> > On Thu, 2012-12-13 at 10:19 -0800, Ben Greear wrote:
> >
> >>> I don't think that's easy, but you're welcome to try. The
> >>> free_sta_work() function references the sdata so it absolutely must run
> >>> at this point.
> >
> >> So, cancel_work_sync(&sdata->work) would appear to remove
> >> all pending sdata->work items from the work-queue.  As long as
> >> there are no other different work items that reference
> >> sdata (and maybe there are..I haven't looked at all of them),
> >> then we should be safe to execute the free_sta_work()
> >> on a different work-queue safely, I think....
> >
> > Sorry, I don't get it. free_sta_work() *itself* has to be executed
> > before the sdata is destroyed. cancel_work_sync(&sdata->work) has
> > nothing to do with free_sta_work.
> 
> My concern is this:
> 
> If I add a different work queue (called destructor-workqueue, perhaps)
> for free_sta_work(), then it only helps
> if I can not block on flushing the current 'big' work-queue.  But, if
> there are items on the big work-queue that reference sdata, then
> that could easily execute after free_sta_work(), and I'm guessing
> that would be very bad.
> 
> So, near where we currently call cancel_work_sync(&sdata->work), I
> think we'd also need to cancel things like the sta->ampdu_mlme.work,
> and probably others as well.
> 
> Then, when we're sure there are no more references to sdata on the
> main-work-queue, it would be safe to flush the destructor-workqueue
> (which would have the fre_sta_work() on it).
> 
> Maybe?

Huh, ok, but I don't think you'll find much that doesn't reference an
sdata?

johannes