From: Cezary Rojewski Date: Tue, 24 Feb 2026 20:56:19 +0000 (+0100) Subject: ALSA: control: Verify put() result when in debug mode X-Git-Tag: v7.1-rc1~166^2~9^2~99 X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=84446536f63d471ab16b2faa25eeab1df21ace0a;p=thirdparty%2Fkernel%2Flinux.git ALSA: control: Verify put() result when in debug mode The put() operation is expected to return: 1) 0 on success if no changes were made 2) 1 on success if changes were made 3) error code otherwise Currently 2) is usually ignored when writing control-operations. While forcing compliance is not an option right now, make it easier for developers to adhere to the expectations and notice problems by logging them when CONFIG_SND_CTL_DEBUG is enabled. Due to large size of struct snd_ctl_elem_value, 'value_buf' is provided as a reusable buffer for kctl->put() verification. This prevents exhausting the stack when verifying the operation. >From user perspective, patch introduces a new trace/events category 'snd_ctl' containing a single 'snd_ctl_put' event type. Log sample: amixer-1086 [003] ..... 8.035939: snd_ctl_put: success: expected=0, actual=0 for ctl numid=1, iface=MIXER, name='Master Playback Volume', index=0, device=0, subdevice=0, card=0 amixer-1087 [003] ..... 8.938721: snd_ctl_put: success: expected=1, actual=1 for ctl numid=1, iface=MIXER, name='Master Playback Volume', index=0, device=0, subdevice=0, card=0 amixer-1088 [003] ..... 9.631470: snd_ctl_put: success: expected=1, actual=1 for ctl numid=1, iface=MIXER, name='Master Playback Volume', index=0, device=0, subdevice=0, card=0 amixer-1089 [000] ..... 9.636786: snd_ctl_put: fail: expected=1, actual=0 for ctl numid=5, iface=MIXER, name='Loopback Mute', index=0, device=0, subdevice=0, card=0 Signed-off-by: Cezary Rojewski Reviewed-by: Mark Brown Reviewed-by: Jaroslav Kysela Signed-off-by: Takashi Iwai Link: https://patch.msgid.link/20260224205619.584795-1-cezary.rojewski@intel.com --- diff --git a/include/sound/core.h b/include/sound/core.h index 64327e9711222..4093ec82a0a12 100644 --- a/include/sound/core.h +++ b/include/sound/core.h @@ -133,6 +133,9 @@ struct snd_card { #ifdef CONFIG_SND_DEBUG struct dentry *debugfs_root; /* debugfs root for card */ #endif +#ifdef CONFIG_SND_CTL_DEBUG + struct snd_ctl_elem_value *value_buf; /* buffer for kctl->put() verification */ +#endif #ifdef CONFIG_PM unsigned int power_state; /* power state */ diff --git a/sound/core/Makefile b/sound/core/Makefile index 31a0623cc89d1..fdd3bb6e81a99 100644 --- a/sound/core/Makefile +++ b/sound/core/Makefile @@ -23,6 +23,7 @@ snd-pcm-$(CONFIG_SND_PCM_IEC958) += pcm_iec958.o # for trace-points CFLAGS_pcm_lib.o := -I$(src) CFLAGS_pcm_native.o := -I$(src) +CFLAGS_control.o := -I$(src) snd-pcm-dmaengine-y := pcm_dmaengine.o diff --git a/sound/core/control.c b/sound/core/control.c index 934e84e938380..374e703d15a91 100644 --- a/sound/core/control.c +++ b/sound/core/control.c @@ -19,6 +19,13 @@ #include #include +#ifdef CONFIG_SND_CTL_DEBUG +#define CREATE_TRACE_POINTS +#include "control_trace.h" +#else +#define trace_snd_ctl_put(card, kctl, iname, expected, actual) +#endif + // Max allocation size for user controls. static int max_user_ctl_alloc_size = 8 * 1024 * 1024; module_param_named(max_user_ctl_alloc_size, max_user_ctl_alloc_size, int, 0444); @@ -1264,6 +1271,72 @@ static int snd_ctl_elem_read_user(struct snd_card *card, return result; } +#if IS_ENABLED(CONFIG_SND_CTL_DEBUG) + +static const char *const snd_ctl_elem_iface_names[] = { + [SNDRV_CTL_ELEM_IFACE_CARD] = "CARD", + [SNDRV_CTL_ELEM_IFACE_HWDEP] = "HWDEP", + [SNDRV_CTL_ELEM_IFACE_MIXER] = "MIXER", + [SNDRV_CTL_ELEM_IFACE_PCM] = "PCM", + [SNDRV_CTL_ELEM_IFACE_RAWMIDI] = "RAWMIDI", + [SNDRV_CTL_ELEM_IFACE_TIMER] = "TIMER", + [SNDRV_CTL_ELEM_IFACE_SEQUENCER] = "SEQUENCER", +}; + +static int snd_ctl_put_verify(struct snd_card *card, struct snd_kcontrol *kctl, + struct snd_ctl_elem_value *control) +{ + struct snd_ctl_elem_value *original = card->value_buf; + struct snd_ctl_elem_info info; + const char *iname; + int ret, retcmp; + + memset(original, 0, sizeof(*original)); + memset(&info, 0, sizeof(info)); + + ret = kctl->info(kctl, &info); + if (ret) + return ret; + + ret = kctl->get(kctl, original); + if (ret) + return ret; + + ret = kctl->put(kctl, control); + if (ret < 0) + return ret; + + /* Sanitize the new value (control->value) before comparing. */ + fill_remaining_elem_value(control, &info, 0); + + /* With known state for both new and original, do the comparison. */ + retcmp = memcmp(&original->value, &control->value, sizeof(original->value)); + if (retcmp) + retcmp = 1; + + iname = snd_ctl_elem_iface_names[kctl->id.iface]; + trace_snd_ctl_put(&kctl->id, iname, card->number, ret, retcmp); + + return ret; +} + +static int snd_ctl_put(struct snd_card *card, struct snd_kcontrol *kctl, + struct snd_ctl_elem_value *control, unsigned int access) +{ + if ((access & SNDRV_CTL_ELEM_ACCESS_SKIP_CHECK) || + (access & SNDRV_CTL_ELEM_ACCESS_VOLATILE)) + return kctl->put(kctl, control); + + return snd_ctl_put_verify(card, kctl, control); +} +#else +static inline int snd_ctl_put(struct snd_card *card, struct snd_kcontrol *kctl, + struct snd_ctl_elem_value *control, unsigned int access) +{ + return kctl->put(kctl, control); +} +#endif + static int snd_ctl_elem_write(struct snd_card *card, struct snd_ctl_file *file, struct snd_ctl_elem_value *control) { @@ -1300,7 +1373,8 @@ static int snd_ctl_elem_write(struct snd_card *card, struct snd_ctl_file *file, false); } if (!result) - result = kctl->put(kctl, control); + result = snd_ctl_put(card, kctl, control, vd->access); + if (result < 0) { up_write(&card->controls_rwsem); return result; diff --git a/sound/core/control_trace.h b/sound/core/control_trace.h new file mode 100644 index 0000000000000..d30e654b08602 --- /dev/null +++ b/sound/core/control_trace.h @@ -0,0 +1,55 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#undef TRACE_SYSTEM +#define TRACE_SYSTEM snd_ctl + +#if !defined(_TRACE_SND_CTL_H) || defined(TRACE_HEADER_MULTI_READ) +#define _TRACE_SND_CTL_H + +#include +#include + +TRACE_EVENT(snd_ctl_put, + + TP_PROTO(struct snd_ctl_elem_id *id, const char *iname, unsigned int card, + int expected, int actual), + + TP_ARGS(id, iname, card, expected, actual), + + TP_STRUCT__entry( + __field(unsigned int, numid) + __string(iname, iname) + __string(kname, id->name) + __field(unsigned int, index) + __field(unsigned int, device) + __field(unsigned int, subdevice) + __field(unsigned int, card) + __field(int, expected) + __field(int, actual) + ), + + TP_fast_assign( + __entry->numid = id->numid; + __assign_str(iname); + __assign_str(kname); + __entry->index = id->index; + __entry->device = id->device; + __entry->subdevice = id->subdevice; + __entry->card = card; + __entry->expected = expected; + __entry->actual = actual; + ), + + TP_printk("%s: expected=%d, actual=%d for ctl numid=%d, iface=%s, name='%s', index=%d, device=%d, subdevice=%d, card=%d\n", + __entry->expected == __entry->actual ? "success" : "fail", + __entry->expected, __entry->actual, __entry->numid, + __get_str(iname), __get_str(kname), __entry->index, + __entry->device, __entry->subdevice, __entry->card) +); + +#endif /* _TRACE_SND_CTL_H */ + +/* This part must be outside protection */ +#undef TRACE_INCLUDE_PATH +#define TRACE_INCLUDE_PATH . +#define TRACE_INCLUDE_FILE control_trace +#include diff --git a/sound/core/init.c b/sound/core/init.c index 2f1bd9cbdbedf..0c316189e9476 100644 --- a/sound/core/init.c +++ b/sound/core/init.c @@ -362,6 +362,11 @@ static int snd_card_init(struct snd_card *card, struct device *parent, #ifdef CONFIG_SND_DEBUG card->debugfs_root = debugfs_create_dir(dev_name(&card->card_dev), sound_debugfs_root); +#endif +#ifdef CONFIG_SND_CTL_DEBUG + card->value_buf = kmalloc(sizeof(*card->value_buf), GFP_KERNEL); + if (!card->value_buf) + return -ENOMEM; #endif return 0; @@ -587,6 +592,9 @@ static int snd_card_do_free(struct snd_card *card) snd_device_free_all(card); if (card->private_free) card->private_free(card); +#ifdef CONFIG_SND_CTL_DEBUG + kfree(card->value_buf); +#endif if (snd_info_card_free(card) < 0) { dev_warn(card->dev, "unable to free card info\n"); /* Not fatal error */