[added to the 4.1 stable tree] ALSA: hda - Fix possible race on regmap bypass flip
From: Sasha Levin <hidden>
Date: 2016-07-12 02:57:05
Subsystem:
sound, the rest · Maintainers:
Jaroslav Kysela, Takashi Iwai, Linus Torvalds
From: Takashi Iwai <redacted> This patch has been added to the 4.1 stable tree. If you have any objections, please let us know. =============== [ Upstream commit 3194ed497939c6448005542e3ca4fa2386968fa0 ] HD-audio driver uses regmap cache bypass feature for reading a raw value without the cache. But this is racy since both the cached and the uncached reads may occur concurrently. The former is done via the normal control API access while the latter comes from the proc file read. Even though the regmap itself has the protection against the concurrent accesses, the flag set/reset is done without the protection, so it may lead to inconsistent state of bypass flag that doesn't match with the current read and occasionally result in a kernel WARNING like: WARNING: CPU: 3 PID: 2731 at drivers/base/regmap/regcache.c:499 regcache_cache_only+0x78/0x93 One way to work around such a problem is to wrap with a mutex. But in this case, the solution is simpler: for the uncached read, we just skip the regmap and directly calls its accessor. The verb execution there is protected by itself, so basically it's safe to call individually. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=116171 Signed-off-by: Takashi Iwai <redacted> Signed-off-by: Sasha Levin <redacted> --- include/sound/hda_regmap.h | 2 ++ sound/hda/hdac_device.c | 10 ++++------ sound/hda/hdac_regmap.c | 40 ++++++++++++++++++++++++++++------------ 3 files changed, 34 insertions(+), 18 deletions(-)
diff --git a/include/sound/hda_regmap.h b/include/sound/hda_regmap.h
index df70590..2f48d64 100644
--- a/include/sound/hda_regmap.h
+++ b/include/sound/hda_regmap.h@@ -17,6 +17,8 @@ int snd_hdac_regmap_add_vendor_verb(struct hdac_device *codec, unsigned int verb); int snd_hdac_regmap_read_raw(struct hdac_device *codec, unsigned int reg, unsigned int *val); +int snd_hdac_regmap_read_raw_uncached(struct hdac_device *codec, + unsigned int reg, unsigned int *val); int snd_hdac_regmap_write_raw(struct hdac_device *codec, unsigned int reg, unsigned int val); int snd_hdac_regmap_update_raw(struct hdac_device *codec, unsigned int reg,
diff --git a/sound/hda/hdac_device.c b/sound/hda/hdac_device.c
index 961ca32..37f2dac 100644
--- a/sound/hda/hdac_device.c
+++ b/sound/hda/hdac_device.c@@ -261,13 +261,11 @@ EXPORT_SYMBOL_GPL(_snd_hdac_read_parm); int snd_hdac_read_parm_uncached(struct hdac_device *codec, hda_nid_t nid, int parm) { - int val; + unsigned int cmd, val; - if (codec->regmap) - regcache_cache_bypass(codec->regmap, true); - val = snd_hdac_read_parm(codec, nid, parm); - if (codec->regmap) - regcache_cache_bypass(codec->regmap, false); + cmd = snd_hdac_regmap_encode_verb(nid, AC_VERB_PARAMETERS) | parm; + if (snd_hdac_regmap_read_raw_uncached(codec, cmd, &val) < 0) + return -1; return val; } EXPORT_SYMBOL_GPL(snd_hdac_read_parm_uncached);
diff --git a/sound/hda/hdac_regmap.c b/sound/hda/hdac_regmap.c
index b0ed870..c785e5a 100644
--- a/sound/hda/hdac_regmap.c
+++ b/sound/hda/hdac_regmap.c@@ -420,14 +420,30 @@ int snd_hdac_regmap_write_raw(struct hdac_device *codec, unsigned int reg, EXPORT_SYMBOL_GPL(snd_hdac_regmap_write_raw); static int reg_raw_read(struct hdac_device *codec, unsigned int reg, - unsigned int *val) + unsigned int *val, bool uncached) { - if (!codec->regmap) + if (uncached || !codec->regmap) return hda_reg_read(codec, reg, val); else return regmap_read(codec->regmap, reg, val); } +static int __snd_hdac_regmap_read_raw(struct hdac_device *codec, + unsigned int reg, unsigned int *val, + bool uncached) +{ + int err; + + err = reg_raw_read(codec, reg, val, uncached); + if (err == -EAGAIN) { + err = snd_hdac_power_up_pm(codec); + if (!err) + err = reg_raw_read(codec, reg, val, uncached); + snd_hdac_power_down_pm(codec); + } + return err; +} + /** * snd_hdac_regmap_read_raw - read a pseudo register with power mgmt * @codec: the codec object
@@ -439,19 +455,19 @@ static int reg_raw_read(struct hdac_device *codec, unsigned int reg, int snd_hdac_regmap_read_raw(struct hdac_device *codec, unsigned int reg, unsigned int *val) { - int err; - - err = reg_raw_read(codec, reg, val); - if (err == -EAGAIN) { - err = snd_hdac_power_up_pm(codec); - if (!err) - err = reg_raw_read(codec, reg, val); - snd_hdac_power_down_pm(codec); - } - return err; + return __snd_hdac_regmap_read_raw(codec, reg, val, false); } EXPORT_SYMBOL_GPL(snd_hdac_regmap_read_raw); +/* Works like snd_hdac_regmap_read_raw(), but this doesn't read from the + * cache but always via hda verbs. + */ +int snd_hdac_regmap_read_raw_uncached(struct hdac_device *codec, + unsigned int reg, unsigned int *val) +{ + return __snd_hdac_regmap_read_raw(codec, reg, val, true); +} + /** * snd_hdac_regmap_update_raw - update a pseudo register with power mgmt * @codec: the codec object
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2.5.0