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authorTakashi Iwai <tiwai@suse.de>2015-08-25 16:09:00 +0200
committerTakashi Iwai <tiwai@suse.de>2015-08-26 15:38:25 +0200
commit47ab154593827b1a8f0713a2b9dd445753d551d8 (patch)
tree17d18cafdf9d13b169f50ada290553db8b62fbe7 /sound/usb/endpoint.c
parentb25cf30a013195a69c167209d13c19b90a7450f2 (diff)
downloadlinux-47ab154593827b1a8f0713a2b9dd445753d551d8.tar.bz2
ALSA: usb-audio: Avoid nested autoresume calls
After the recent fix of runtime PM for USB-audio driver, we got a lockdep warning like: ============================================= [ INFO: possible recursive locking detected ] 4.2.0-rc8+ #61 Not tainted --------------------------------------------- pulseaudio/980 is trying to acquire lock: (&chip->shutdown_rwsem){.+.+.+}, at: [<ffffffffa0355dac>] snd_usb_autoresume+0x1d/0x52 [snd_usb_audio] but task is already holding lock: (&chip->shutdown_rwsem){.+.+.+}, at: [<ffffffffa0355dac>] snd_usb_autoresume+0x1d/0x52 [snd_usb_audio] This comes from snd_usb_autoresume() invoking down_read() and it's used in a nested way. Although it's basically safe, per se (as these are read locks), it's better to reduce such spurious warnings. The read lock is needed to guarantee the execution of "shutdown" (cleanup at disconnection) task after all concurrent tasks are finished. This can be implemented in another better way. Also, the current check of chip->in_pm isn't good enough for protecting the racy execution of multiple auto-resumes. This patch rewrites the logic of snd_usb_autoresume() & co; namely, - The recursive call of autopm is avoided by the new refcount, chip->active. The chip->in_pm flag is removed accordingly. - Instead of rwsem, another refcount, chip->usage_count, is introduced for tracking the period to delay the shutdown procedure. At the last clear of this refcount, wake_up() to the shutdown waiter is called. - The shutdown flag is replaced with shutdown atomic count; this is for reducing the lock. - Two new helpers are introduced to simplify the management of these refcounts; snd_usb_lock_shutdown() increases the usage_count, checks the shutdown state, and does autoresume. snd_usb_unlock_shutdown() does the opposite. Most of mixer and other codes just need this, and simply returns an error if it receives an error from lock. Fixes: 9003ebb13f61 ('ALSA: usb-audio: Fix runtime PM unbalance') Reported-and-tested-by: Alexnader Kuleshov <kuleshovmail@gmail.com> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/usb/endpoint.c')
-rw-r--r--sound/usb/endpoint.c10
1 files changed, 6 insertions, 4 deletions
diff --git a/sound/usb/endpoint.c b/sound/usb/endpoint.c
index 03b074419964..e6f71894ecdc 100644
--- a/sound/usb/endpoint.c
+++ b/sound/usb/endpoint.c
@@ -355,8 +355,10 @@ static void snd_complete_urb(struct urb *urb)
if (unlikely(urb->status == -ENOENT || /* unlinked */
urb->status == -ENODEV || /* device removed */
urb->status == -ECONNRESET || /* unlinked */
- urb->status == -ESHUTDOWN || /* device disabled */
- ep->chip->shutdown)) /* device disconnected */
+ urb->status == -ESHUTDOWN)) /* device disabled */
+ goto exit_clear;
+ /* device disconnected */
+ if (unlikely(atomic_read(&ep->chip->shutdown)))
goto exit_clear;
if (usb_pipeout(ep->pipe)) {
@@ -529,7 +531,7 @@ static int deactivate_urbs(struct snd_usb_endpoint *ep, bool force)
{
unsigned int i;
- if (!force && ep->chip->shutdown) /* to be sure... */
+ if (!force && atomic_read(&ep->chip->shutdown)) /* to be sure... */
return -EBADFD;
clear_bit(EP_FLAG_RUNNING, &ep->flags);
@@ -868,7 +870,7 @@ int snd_usb_endpoint_start(struct snd_usb_endpoint *ep, bool can_sleep)
int err;
unsigned int i;
- if (ep->chip->shutdown)
+ if (atomic_read(&ep->chip->shutdown))
return -EBADFD;
/* already running? */