On Tue, 15 Aug 2023 23:32:31 +0200, Curtis Malainey wrote: > > On Tue, Aug 15, 2023 at 9:07 AM Takashi Iwai <tiwai@xxxxxxx> wrote: > > > > On Mon, 14 Aug 2023 22:20:29 +0200, > > Curtis Malainey wrote: > > > > > > On Sun, Aug 13, 2023 at 1:08 AM Takashi Iwai <tiwai@xxxxxxx> wrote: > > > > > > > > On Wed, 09 Aug 2023 23:11:45 +0200, > > > > Curtis Malainey wrote: > > > > > > > > > > > > > > > > > And now looking back at kobj code and device code, they do refcount > > > > > > parent objects. Maybe the problem is in our side -- the all devices > > > > > > are created with the original real device as the parent, including the > > > > > > card_dev, while there are some dependencies among children. So, if we > > > > > > build up a proper tree, pci_dev -> card_dev -> ctl_dev, pcm_dev, etc, > > > > > > one of the problems could be solved. It's more or less similar as > > > > > > what I suggested initially (referring card_dev at pcm), while changing > > > > > > the parent would make it implicitly. > > > > > > > > > > Yes I think this would be the long term proper way to go, that way > > > > > parents just put children and remove their reference, then they > > > > > cleanup on their own time making everyone happy. My first patch was a > > > > > very lazy attempt that, if we wanted to do the right thing we would > > > > > obviously have to split the structs and free functions to operate in > > > > > their own release. If you have time feel free to take another swing at > > > > > the patches, otherwise I won't be able to start until next week. > > > > > > > > Now looking back at the problem again, I noticed that actually my > > > > previous comment was wrong: as default, the device dependencies aren't > > > > kept at the release time, but it's already cleared at device_del() > > > > call. The device_del() calls kobject_del() and put_device(parent). > > > > So after this moment, both device releases become independent, and > > > > it'll hit a problem if the released object has still some dependency > > > > (such as the case of card vs ctl_dev in our case). > > > > > > > > An extra dependency to card_dev as I put in my early patch would "fix" > > > > it. But, there is yet another problem: the call of dev_free call for > > > > snd_device object with SNDRV_DEV_LOWLEVEL can happen before releasing > > > > PCM and other devices when the delayed kobj release is enabled. And, > > > > usually this callback does release the top-level resources, which > > > > might be still accessed during the other releases. > > > > > > > > > I was doing some testing late last week that confirms these fears > > > actually. Basically the rig was opening a non-blocking PCM and just > > > never sending data, removing the hw sound device (in this case a USB > > > peripheral) but not closing the userspace app. As a result kobjects > > > were released out of order with the top level "sound" being released > > > at disconnect of the USB device, but the actual card not being > > > released until the app closed. See annotated logs below > > > > > > [ 690.528577] kobject: 'sound' (00000000266cd308): > > > kobject_add_internal: parent: '3-9:1.0', set: '(null)' <----- plug in > > > device > > > [ 690.528607] kobject: 'card1' (00000000f7fa0903): > > > kobject_add_internal: parent: 'sound', set: 'devices' > > > [ 690.528732] kobject: 'card1' (00000000f7fa0903): kobject_uevent_env > > > [ 690.528756] kobject: 'card1' (00000000f7fa0903): fill_kobj_path: > > > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1' > > > [ 690.528988] kobject: 'pcmC1D0p' (0000000095ff4473): > > > kobject_add_internal: parent: 'card1', set: 'devices' > > > [ 690.529640] kobject: 'pcmC1D0p' (0000000095ff4473): fill_kobj_path: > > > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/pcmC1D0p' > > > [ 690.529778] kobject: 'pcmC1D0c' (00000000c4879d24): > > > kobject_add_internal: parent: 'card1', set: 'devices' > > > [ 690.530006] kobject: 'pcmC1D0c' (00000000c4879d24): fill_kobj_path: > > > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/pcmC1D0c' > > > [ 690.530108] kobject: 'controlC1' (00000000a0a25449): > > > kobject_add_internal: parent: 'card1', set: 'devices' > > > [ 690.530373] kobject: 'controlC1' (00000000a0a25449): > > > fill_kobj_path: path = > > > '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/controlC1' > > > [ 690.671889] kobject: 'card1' (00000000f7fa0903): kobject_uevent_env > > > [ 690.671906] kobject: 'card1' (00000000f7fa0903): fill_kobj_path: > > > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1' > > > [ 700.009244] kobject: 'controlC1' (00000000a0a25449): > > > fill_kobj_path: path = > > > '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/controlC1' > > > [ 700.010131] kobject: 'pcmC1D0p' (0000000095ff4473): fill_kobj_path: > > > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/pcmC1D0p' > > > [ 700.011344] kobject: 'pcmC1D0c' (00000000c4879d24): fill_kobj_path: > > > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/pcmC1D0c' > > > [ 700.012916] kobject: 'card1' (00000000f7fa0903): kobject_uevent_env > > > [ 700.012951] kobject: 'card1' (00000000f7fa0903): fill_kobj_path: > > > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1' > > > <---- start blocked playback here > > > [ 700.013057] kobject: 'sound' (00000000266cd308): kobject_release, > > > parent 0000000000000000 (delayed 1000) <--- unplug usb device > > > [ 701.054221] kobject: 'sound' (00000000266cd308): kobject_cleanup, > > > parent 0000000000000000 > > > [ 701.054236] kobject: 'sound' (00000000266cd308): calling ktype release > > > [ 701.054257] kobject: 'sound': free name > > > [ 713.639843] kobject: 'card1' (00000000f7fa0903): kobject_release, > > > parent 0000000000000000 (delayed 3000) <--- Send EOF to playback > > > stream > > > [ 716.669776] kobject: 'card1' (00000000f7fa0903): kobject_cleanup, > > > parent 0000000000000000 > > > [ 716.669810] kobject: 'card1' (00000000f7fa0903): calling ktype release > > > [ 716.670834] kobject: 'card1': free name > > > > > > > > > > > > > > > So, if we tie the object resource with each struct device release, we > > > > have a lot of works: > > > > 1. Add extra dependencies among device hierarchy > > > > 2. Don't use card_dev refcount for managing the sync to device closes, > > > > introduce another kref instead; otherwise card_dev refcount would > > > > never reach to zero > > > > 3. Fix race of devres vs card_dev release > > > > 4. Move the second half part of snd_card_do_free() to the release > > > > callback of card_dev itself to sync with the top-level release > > > > 5. Rewrite all SNDRV_DEV_LOWLEVEL usages to be called via > > > > card->private_free or such; > > > > maybe the only problem is hda_intel.c and hda_tegra.c that need > > > > some work at the disconnection time, and we may introduce another > > > > hook in the card object to replace that > > > > > > > > And, at this moment, I feel that it'd be easier to go back to the > > > > early way of device management, i.e. it'll be just like your patch, > > > > managing the device object independently from the rest resources. > > > > (This means also that the way freeing the resource for hwdep and > > > > rawmidi will go back again without the embedded device, too; they > > > > also suffer from the same problem of .) > > > > > > I agree, I think as a simple stopgap, my earlier patch would at least > > > appease the test until we can figure out the best way to do some > > > heavier work on the kobj. I think the proxy pointer for devres would > > > also be the best short term for 3. > > > > > > > > > > > The change 2 and 3 above can be still applied with your change, which > > > > will fix the remaining devres-vs-card_dev problem. > > > > > > I am not sure I follow the need for 2. If we broke ctl_dev out into > > > its own memory region and structured everything as a proper tree we > > > would have a proper cleanup and be able to use the refcounting > > > properly. > > > > My thought was about the devres release that does kfree() of the card > > while the card's card_dev release itself is still delayed. > > This might be a needless fear, though, as snd_card_free() should sync > > with the actual card_dev release. > > > > But, splitting the release-trigger and the actual memory release could > > be still worth. > > > > > > Once after fixing the current problem, we may work further on other > > > > stuff (e.g. item 5), so that we can switch again to the device-release > > > > model eventually later, too. > > > > > > Agreed, I don't have any experience with SNDRV_DEV_LOWLEVEL but I am > > > happy to help out here where I can. > > > > > > I am going to see if I can split the release card as mentioned but > > > also have refcount work as expected and have the release calls roll up > > > the tree. > > > > I quickly worked on and made a patch series. > > It's put in topic/dev-split branch of sound git tree > > https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/log/?h=topic/dev-split > > > > It'd be appreciated if you can review / test it. > > Took a look and ran it through the tests > > You need to apply this diff Thanks, I'll fix it up. > > diff --git a/sound/usb/media.c b/sound/usb/media.c > index 6d11fedb46326..d48db6f3ae659 100644 > --- a/sound/usb/media.c > +++ b/sound/usb/media.c > @@ -35,7 +35,7 @@ int snd_media_stream_init(struct snd_usb_substream > *subs, struct snd_pcm *pcm, > { > struct media_device *mdev; > struct media_ctl *mctl; > - struct device *pcm_dev = &pcm->streams[stream].dev; > + struct device *pcm_dev = pcm->streams[stream].dev; > u32 intf_type; > int ret = 0; > u16 mixer_pad; > > Hammering probe and remove appears to be fine. Went 45min without issue. > > Userspace holding references past hw removal appears to still be > broken as sound is released while the app is still running. > > -- remove usb device -- > [ 4819.827476] kobject: 'controlC1' (00000000255a51c8): > fill_kobj_path: path = > '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/controlC1' > [ 4819.828114] kobject: 'pcmC1D0p' (00000000f0627532): kobject_uevent_env > [ 4819.828145] kobject: 'pcmC1D0p' (00000000f0627532): fill_kobj_path: > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/pcmC1D0p' > [ 4819.828822] kobject: 'pcmC1D0c' (000000001b707a15): kobject_uevent_env > [ 4819.828850] kobject: 'pcmC1D0c' (000000001b707a15): fill_kobj_path: > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1/pcmC1D0c' > [ 4819.829405] kobject: 'card1' (000000005bce975e): kobject_uevent_env > [ 4819.829428] kobject: 'card1' (000000005bce975e): fill_kobj_path: > path = '/devices/pci0000:00/0000:00:14.0/usb3/3-9/3-9:1.0/sound/card1' > [ 4819.829516] kobject: 'sound' (000000000bb52434): kobject_release, > parent 0000000000000000 (delayed 4000) > [ 4823.873625] kobject: 'sound' (000000000bb52434): kobject_cleanup, > parent 0000000000000000 > [ 4823.873645] kobject: 'sound' (000000000bb52434): calling ktype release > [ 4823.873654] kobject: 'sound': free name > > -- end app -- > [ 4849.581815] kobject: 'pcmC1D0p' (00000000f0627532): > kobject_release, parent 0000000000000000 (delayed 2000) > [ 4849.581960] kobject: 'pcmC1D0c' (000000001b707a15): > kobject_release, parent 0000000000000000 (delayed 2000) > [ 4849.582626] kobject: 'card1' (000000005bce975e): kobject_release, > parent 0000000000000000 (delayed 1000) > [ 4850.625615] kobject: 'card1' (000000005bce975e): kobject_cleanup, > parent 0000000000000000 > [ 4850.625638] kobject: 'card1' (000000005bce975e): calling ktype release > [ 4850.625663] kobject: 'card1': free name > [ 4851.585647] kobject: 'pcmC1D0c' (000000001b707a15): > kobject_cleanup, parent 0000000000000000 > [ 4851.585672] kobject: 'pcmC1D0c' (000000001b707a15): calling ktype release > [ 4851.585708] kobject: 'pcmC1D0c': free name > [ 4851.585727] kobject: 'pcmC1D0p' (00000000f0627532): > kobject_cleanup, parent 0000000000000000 > [ 4851.585737] kobject: 'pcmC1D0p' (00000000f0627532): calling ktype release > [ 4851.585752] kobject: 'pcmC1D0p': free name It's the designed behavior. Those are device *files* that are deleted immediately at the disconnection while the application is still running. It's for avoiding a new application to be started after the disconnect. That is, only the device files in /dev/snd/* become invisible. Meanwhile, the already opened objects are still handled internally. > I still don't understand why you need the kref. The devices are > already reference counting, why not use them? If we split them up into > their own structs we could then just device_put everything on removal > and let it roll up the tree with releases automatically, blocking > where userspace is still holding references. I will share a patches > sometime this week of what I mean. They will probably be a bit bigger > blast radius but I think its what is needed here. We want to trigger the top-level release free procedure once when all files are closed. This top-level release does put_device() of all belonging devices. The card_dev device refcount was used for this purpose. OTOH, if we want to construct the topology of the devices until the actual deletion (i.e. keep card_dev until pcm and others are really released/deleted), the card_dev refcount will be used for managing the topology, too. So, it'll get a side-effect side-effect that the card_dev refcount won't be zero even after all files are closed (it's referred from the children). So, it's a kind of preparation for the future. Takashi
