Hi, On Sat, Jan 23, 2021 at 10:10:20AM +0100, Takashi Iwai wrote: > On Sat, 23 Jan 2021 04:10:25 +0100, > Takashi Sakamoto wrote: > > > > Hi, > > > > On Fri, Jan 22, 2021 at 03:04:56PM +0100, Takashi Iwai wrote: > > > On Fri, 22 Jan 2021 09:20:32 +0100, > > > Takashi Sakamoto wrote: > > > > > > > > ALSA control core allows usespace application to register control element > > > > set by call of ioctl(2) with SNDRV_CTL_IOCTL_ELEM_ADD request. The added > > > > control elements are called as 'user-defined'. Currently sound card has > > > > limitation on the number of the user-defined control element set up > > > > to 32. > > > > > > > > The limitation is inconvenient to drivers in ALSA firewire stack since > > > > the drivers expect userspace applications to implement function to > > > > control device functionalities such as mixing and routing. As the > > > > userspace application, snd-firewire-ctl-services project starts: > > > > https://github.com/alsa-project/snd-firewire-ctl-services/ > > > > > > > > The project supports many devices supported by ALSA firewire stack. The > > > > limitation is mostly good since routing and mixing controls can be > > > > represented by control element set, which includes multiple control element > > > > with the same parameters. Nevertheless, it's actually inconvenient to > > > > device which has many varied functionalities. For example, plugin effect > > > > such as channel strip and reverb has many parameters. For the case, many > > > > control elements are required to configure the parameters and control > > > > element set cannot aggregates them for the parameters. At present, the > > > > implementations for below models requires more control element sets > > > > than 32: > > > > > > > > * snd-bebob-ctl-service > > > > * Apogee Ensemble (31 sets for 34 elements) > > > > * snd-dice-ctl-service > > > > * TC Electronic Konnekt 24d (78 sets for 94 elements) > > > > * TC Electronic Studio Konnekt 48 (98 sets for 114 elements) > > > > * TC Electronic Konnekt Live (88 sets for 104 elements) > > > > * TC Electronic Impact Twin (70 sets for 86 elements) > > > > * Focusrite Liquid Saffire 56 (37 sets for 52 elements) > > > > > > > > This commit expands the limitation according to requirement from the above > > > > applications. As a result, userspace applications can add control element > > > > sets up to 150 per sound card. It results in 154,200 user-defined control > > > > elements as maximum since one control element set can include 1028 control > > > > elements. > > > > > > Thinking of this change again after reading your description, I find > > > that a more flexible and safer approach would be to limit the number > > > of total elements. That is, count the number of items in each > > > element, and set the max to (32 * MAX_CONTROL_COUNT). This will keep > > > the same max as the current implementation can achieve, while it > > > allows more elements as long as they contain lower number of items. > > > > > > So, something like below (totally untested). > > > > > > > > > thanks, > > > > > > Takashi > > > > > > --- a/sound/core/control.c > > > +++ b/sound/core/control.c > > > @@ -18,10 +18,11 @@ > > > #include <sound/info.h> > > > #include <sound/control.h> > > > > > > -/* max number of user-defined controls */ > > > -#define MAX_USER_CONTROLS 32 > > > #define MAX_CONTROL_COUNT 1028 > > > > > > +/* max number of user-defined controls */ > > > +#define MAX_USER_CONTROLS (32 * MAX_CONTROL_COUNT) > > > + > > > struct snd_kctl_ioctl { > > > struct list_head list; /* list of all ioctls */ > > > snd_kctl_ioctl_func_t fioctl; > > > @@ -520,6 +521,7 @@ static int snd_ctl_remove_user_ctl(struct snd_ctl_file * file, > > > struct snd_card *card = file->card; > > > struct snd_kcontrol *kctl; > > > int idx, ret; > > > + int count; > > > > > > down_write(&card->controls_rwsem); > > > kctl = snd_ctl_find_id(card, id); > > > @@ -536,10 +538,11 @@ static int snd_ctl_remove_user_ctl(struct snd_ctl_file * file, > > > ret = -EBUSY; > > > goto error; > > > } > > > + count = kctl->count; > > > ret = snd_ctl_remove(card, kctl); > > > if (ret < 0) > > > goto error; > > > - card->user_ctl_count--; > > > + card->user_ctl_count -= count; > > > error: > > > up_write(&card->controls_rwsem); > > > return ret; > > > @@ -1435,18 +1438,18 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file, > > > return err; > > > } > > > > > > + /* Check the number of elements for this userspace control. */ > > > + count = info->owner; > > > + if (count == 0) > > > + count = 1; > > > + > > > /* > > > * The number of userspace controls are counted control by control, > > > * not element by element. > > > */ > > > - if (card->user_ctl_count + 1 > MAX_USER_CONTROLS) > > > + if (card->user_ctl_count + count > MAX_USER_CONTROLS) > > > return -ENOMEM; > > > > > > - /* Check the number of elements for this userspace control. */ > > > - count = info->owner; > > > - if (count == 0) > > > - count = 1; > > > - > > > /* Arrange access permissions if needed. */ > > > access = info->access; > > > if (access == 0) > > > @@ -1535,7 +1538,7 @@ static int snd_ctl_elem_add(struct snd_ctl_file *file, > > > * which locks the element. > > > */ > > > > > > - card->user_ctl_count++; > > > + card->user_ctl_count += count; > > > > > > unlock: > > > up_write(&card->controls_rwsem); > > > > I have no objection to any change as long as it allows the service programs > > to add control elements enough for target device. However, it's unclear > > what is flexible and safe in the above patch. > > > > When adding user-defined control element set, some objects are allocated > > for below structures with some variable-length members: > > * struct snd_kcontrol (in include/sound/control.h) > > * struct user_element (in sound/core/control.h) > > > > Current implementation is to avoid too much allocation for the above > > against userspace applications with bugs or mis-programming. It's > > reasonable to limit the allocation according to count of added control > > element set for the purpose. > > > > On the other hand, when counting the number of added control element for > > the limitation, the above becomes loose. In the worst case, the patch > > allows 32,896 sets to be allocated and against comments in my previous > > patch. > > OK, my previous patch was too simplified (I forgot to take the > private_data into account), but the point is that what we want is to > cap the worst case memory consumption. > > If I calculate correctly, user_element is 320 bytes, and the value is > up to 512 bytes for each item, and snd_kcontrol is 144 bytes, and > snd_kcontrol_volatile is 16 bytes per item. And each element may > contain 1028 items. So, the worst case scenario of the memory > consumption is: > (320 + 512*1028 + 144 + 16*1024) * 32 = 17383936 > That is, currently we allow 16MB at most. > > By increasing MAX_USER_CONTROLS to 150, it'll become 77MB. > > And, think what if you'd need to increase more in future, e.g. 512 > elements. The max consumption also increases linearly. > > OTOH, imagine that we cap the memory consumption to 16MB instead of > limiting only the MAX_USER_CONTROLS. This lets user still allow to > allocate more elements with smaller number of items (that is the > common use case). In this way, we don't take a risk of higher memory > consumption while user can deploy the user elements more flexibly. The memory object for data of Type-Length-Value style is underestimate in your calculation for the worst case. For user-defined control element set, the size is (1024 * 128) per control element set[1]. Of cource, it's possible to judge that usual userspace application don't use data of Type-Length-Value style so much. However, we are assuming the worst case now. ``` Objects linearly increased according to the number of user-defined control element sets: * struct snd_kcontrol (144 bytes) * struct user_element (320 bytes) * data of TLV ((1024 * 128) bytes as maximum) Objects linearly increased according to the number of control elements: * data of values (max. 1024 bytes in System V ABI with LP64 data type) * data of snd_kcontrol_volatile (16 bytes) Memory consumption under current limitation: (144 + 320 + 1024 * 128) * 32 + (1024 + 16) * 1028 = 5,278,272 Scenario for the worst case when appying the patch: * adding 32,896 control element sets * for elements: (1024 + 16) * 1028 * 32 = 34,211,840 * for element sets: (144 + 320 + 1024 * 128) * 32896 = 4,327,008,256 Scenario for the worst case when applying my patch: * adding 150 control element sets * for elements: (1024 + 16) * 1028 * 150 = 160,368,000 * for element sets: (144 + 320 + 1024 * 128) * 150 = 19,730,400 ``` [1] https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git/tree/sound/core/control.c#n1299 Regards Takashi Sakamoto
