On Thu, 30 Sep 2021 12:27:53 +0200, John Keeping wrote: > > On Thu, 30 Sep 2021 08:55:52 +0200 > Takashi Iwai <tiwai@xxxxxxx> wrote: > > > On Thu, 30 Sep 2021 08:31:56 +0200, > > Takashi Iwai wrote: > > > > > > On Wed, 29 Sep 2021 18:56:32 +0200, > > > John Keeping wrote: > > > > > > > > On Wed, 29 Sep 2021 17:28:57 +0200 > > > > Takashi Iwai <tiwai@xxxxxxx> wrote: > > > > > > > > > On Wed, 29 Sep 2021 17:17:58 +0200, > > > > > John Keeping wrote: > > > > > > > > > > > > On Wed, 29 Sep 2021 16:51:47 +0200 > > > > > > Takashi Iwai <tiwai@xxxxxxx> wrote: > > > > > > > > > > > > > On Wed, 29 Sep 2021 13:36:20 +0200, > > > > > > > John Keeping wrote: > > > > > > > > > > > > > > > > If the sequencer device outlives the rawmidi device, then > > > > > > > > snd_rawmidi_dev_seq_free() will run after release_rawmidi_device() has > > > > > > > > freed the snd_rawmidi structure. > > > > > > > > > > > > > > > > This can easily be reproduced with CONFIG_DEBUG_KOBJECT_RELEASE. > > > > > > > > > > > > > > > > Keep a reference to the rawmidi device until the sequencer has been > > > > > > > > destroyed in order to avoid this. > > > > > > > > > > > > > > > > Signed-off-by: John Keeping <john@xxxxxxxxxxxx> > > > > > > > > > > > > > > Thanks for the patch. I wonder, though, how this could be triggered. > > > > > > > Is this the case where the connected sequencer device is being used > > > > > > > while the sound card gets released? Or is it something else? > > > > > > > > > > > > I'm not sure if it's possible to trigger via the ALSA API; I haven't > > > > > > found a route that can trigger it, but that doesn't mean there isn't > > > > > > one :-) > > > > > > > > > > > > Mostly this is useful to make CONFIG_DEBUG_KOBJECT_RELEASE cleaner. > > > > > > > > > > Hm, then could you check whether the patch below papers over it > > > > > instead? > > > > > > > > No, this patch doesn't solve it. The issue is that the effect of the > > > > final device_put() is delayed from the time it is called and there is no > > > > way to guarantee the ordering without ensuring the sequencer has been > > > > destroyed before the final reference to the rawmidi device is put. > > > > > > > > Both of the functions involved are called from the core > > > > device::release() hook. > > > > > > > > I'm using the patch below to easily check that the sequencer has been > > > > freed before the rawmidi data. This can easily be triggered by > > > > unplugging a USB MIDI device (it's not 100% since the kobject release > > > > delays are random). > > > > > > Hm, it's strange. I suppose you're *not* using the MIDI device, > > > right? > > > > > > The release path for the USB-audio driver is: > > > usb_audio_disconnect() -> > > > snd_card_free_when_closed() -> > > > release_card_device() (via put_device(&card->card_dev)) -> > > > snd_card_do_free() > > > > > > And here in snd_card_do_free(), the snd_device free-callback chains > > > are called at the beginning (snd_device_free_all()). > > > As it's executed in a reverse loop, snd_rawmidi_dev_seq_free() shall > > > be called before snd_rawmidi_dev_free(). Since the final put_device() > > > for the rawmidi device is called in the latter function, the device > > > release must not happen before snd_rawmidi_dev_seq_free()... > > > > Correction: now I finally understood what I misunderstood. > > Although the snd_device call chain mentioned above itself is correct, > > the snd_rawmidi_dev_seq_free() function isn't called directly from the > > snd_device chain, but it's rater the own private_free of > > snd_seq_device object. That is, the call of snd_seq_device > > private_free is done in a wrong place; it should be called in the > > snd_device call chain instead of the device release. > > > > A fix patch is something like below. Could you check whether this > > fixes the problem? > > Yes, this fixes it! Great, I'll submit a proper patch. Thanks! Takashi
