Task1 waits for mutex_lock, and task2 waits for pde to be unused.(deadlock)
/*call trace*/
task1 Call trace:
__switch_to+0x174/0x338
schedule+0x7c/0xe8
schedule_preempt_disabled+0x24/0x40
mutex_lock+0x40/0xec
snd_info_text_entry_open+0x28/0x120
proc_reg_open+0xe4/0x248
do_dentry_open+0x2a4/0x4e0
task2 Call trace:
schedule_timeout+0x44/0x1c8
wait_for_completion+0x18/0x24
proc_entry_rundown+0x60/0xf0
remove_proc_subtree+0x180/0x218
proc_remove+0x20/0x30
snd_info_disconnect+0x4c/0x68
snd_info_card_disconnect+0x3c/0x58
snd_card_disconnect+0x130/0x264
usb_audio_disconnect+0xc0/0x24c
/*the sequence*/
task1:
- proc_reg_open: set the use_pde
task2:
- usb_audio_disconnect: usb device disconnection occurs
- snd_info_card_disconnect: acquire the mutex_lock(&info_mutex)
- proc_entry_rundown: wait_for_completion(unuse_pde)
task1:
- wait for mutex_lock in snd_info_text_entry_open
To avoid it, a mutex without wating(mutex_trylock) shoud be used in
snd_info_text_entry_open(task1).
Then, when mutex_lock acquisition fails, an error is returned, and the pde
becomes unused, and the mutex_lock held by task2 is released.
Signed-off-by: Shinhyung Kang <s47.kang@xxxxxxxxxxx>
diff --git a/sound/core/info.c b/sound/core/info.c
index 0b2f04dcb589..6cb4064b292e 100644
--- a/sound/core/info.c
+++ b/sound/core/info.c
@@ -369,7 +369,10 @@ static int snd_info_text_entry_open(struct inode
*inode, struct file *file)
struct snd_info_private_data *data;
int err;
- mutex_lock(&info_mutex);
+ if (!mutex_trylock(&info_mutex)) {
+ pr_err("%s: failed to acquire the info_mutex\n", __func__);
+ return -EAGAIN;
+ }
err = alloc_info_private(entry, &data);
if (err < 0)
goto unlock;
