On Sat, 05 Aug 2023 10:09:58 +0200, Takashi Iwai wrote: > > On Fri, 04 Aug 2023 21:17:56 +0200, > Curtis Malainey wrote: > > > > On Fri, Aug 4, 2023 at 1:58 AM Takashi Iwai <tiwai@xxxxxxx> wrote: > > > > > > Now I've been reconsidering the problem, and thought of another > > > possible workaround. We may add the card's refcount control for the > > > device init and release, so that we delay the actual resource free. > > > The basic idea is to take card->card_ref at the device init and unref > > > it at the actual device release callback. Then the snd_card_free() > > > call is held until all those refcounted devices are released. > > > > > > Below is a PoC patch (yes, this can be split, too ;) > > > A quick test on VM seems OK, but needs more reviews and tests. > > > > > > It contains somewhat ugly conditional put_device() at the dev_free > > > ops. We can make those a bit saner with some helpers later, too. > > > > > > BTW, this approach may avoid another potential problem by the delayed > > > release; if we finish the driver remove without waiting for the actual > > > device releases, it may hit a code (the piece of the device release > > > callback) of the already removed module, and it's not guaranteed to be > > > present. > > > I'm not sure whether this really happens, but it's another thing to be > > > considered. > > > > > > > > > thanks, > > > > > > Takashi > > > > > > --- > > > diff --git a/include/sound/core.h b/include/sound/core.h > > > index f6e0dd648b80..00c514a80a4a 100644 > > > --- a/include/sound/core.h > > > +++ b/include/sound/core.h > > > > Unfortunately it doesn't hold up in my testing, hit the devm vs device > > race bug after a little over 30min of hammering snd-dummy (on top of > > your for-next branch) > (snip) > > I was talking with Stephen Boyd about this bug and his recommendation > > was to keep snd_card always out of devm and just allocate a pointer in > > devm to snd_card to puppet it as if it was managed via devm and just > > reference count rather than release the card so that its always > > handled through device->release. What do you think? This would go > > alongside the current patch proposed. > > Indeed, that's another issue about devres vs delayed kobj release. > A quick fix would be something like below, I suppose. > (note: totally untested) Scratch it. It's still obviously broken. Will cook more proper patches later. Takashi
