On Wed, 26 Jun 2019 22:34:28 +0200, Evan Green wrote: > > On Wed, Jun 26, 2019 at 1:27 AM Takashi Iwai <tiwai@xxxxxxx> wrote: > > > > On Tue, 25 Jun 2019 23:54:18 +0200, > > Evan Green wrote: > > > > > > The normal flow through the widget sysfs codepath is that > > > snd_hdac_refresh_widgets() is called once without the sysfs bool set > > > to set up codec->num_nodes and friends, then another time with the > > > bool set to actually allocate all the sysfs widgets. However, during > > > the first time allocation, hda_widget_sysfs_reinit() ignores the new > > > num_nodes passed in via parameter and just calls hda_widget_sysfs_init(), > > > using whatever was in codec->num_nodes before the update. This is not > > > correct in cases where num_nodes changes. Here's an example: > > > > > > Sometime earlier: > > > snd_hdac_refresh_widgets(hdac, false) > > > sets codec->num_nodes to 2, widgets is still not allocated > > > > > > Now: > > > snd_hdac_refresh_widgets(hdac, true) > > > hda_widget_sysfs_reinit(num_nodes=7) > > > hda_widget_sysfs_init() > > > widget_tree_create() > > > alloc(codec->num_nodes) // this is still 2 > > > codec->num_nodes = 7 > > > > > > Pass num_nodes and start_nid down into widget_tree_create() so that > > > the right number of nodes are allocated in all cases. > > > > > > Signed-off-by: Evan Green <evgreen@xxxxxxxxxxxx> > > > > Thanks for the patch. That's indeed a problem, but I guess a simpler > > approach is just to return if sysfs didn't exist. If the sysfs > > entries aren't present at the second call with sysfs=true, it implies > > that the codec object will be exposed anyway later, and the sysfs will > > be created there. So, something like below would work instead? > > Hi Takashi, > Thanks for taking a look. I'm not sure you'd want to do that because > then you end up returning from sysfs_reinit without having allocated > any of the sysfs widgets. You'd be relying on the implicit behavior > that another call to init is coming later (despite having updated > num_nodes and start node), which is difficult to follow and easy to > break. In my opinion the slight bit of extra diffs is well worth the > clarity of having widget_tree_create always allocate the correct > start/count. Well, skipping is the right behavior, actually. The whole need of the refresh function is just to refresh the widget list, and the current behavior to create a sysfs is rather superfluous. This action has never been used, so better to get removed for avoiding misuse. > Actually, in looking at the widget lock patch, I don't think it's > sufficient either. It adds a lock around sysfs_reinit, but the setting > of codec->num_nodes and codec->start_nid is unprotected by the lock. > So you could have the two threads politely serialize through > sysfs_reinit, but then get reordered before setting codec->num_nodes, > landing you with an array whose length doesn't match num_nodes. The usage of snd_hdac_refresh_widgets() is supposed to be done only at the codec probe phase, hence there is no lock done in the core code; IOW, any concurrent access has to be protected in the caller side in general. Have you actually seen such concurrent accesses? If yes, that's a problem in the usage. thanks, Takashi > > Let me craft up an additional patch to fix the locking. > -Evan > > > > > > > thanks, > > > > Takashi > > > > --- a/sound/hda/hdac_sysfs.c > > +++ b/sound/hda/hdac_sysfs.c > > @@ -428,7 +428,7 @@ int hda_widget_sysfs_reinit(struct hdac_device *codec, > > int i; > > > > if (!codec->widgets) > > - return hda_widget_sysfs_init(codec); > > + return 0; > > > > tree = kmemdup(codec->widgets, sizeof(*tree), GFP_KERNEL); > > if (!tree) > _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
