[PATCH] tpm: fix WARNING: lock held when returning to user space

[Tadeusz Struk <tadeusz.struk@intel.com>]

When an application sends TPM commands in NONBLOCKING mode
the driver holds chip->tpm_mutex returning from write(),
which triggers WARNING: lock held when returning to user space!
To silence this warning the driver needs to release the mutex
and acquire it again in tpm_dev_async_work() before sending
the command.

Cc: stable@vger.kernel.org
Fixes: 9e1b74a63f776 (tpm: add support for nonblocking operation)
Signed-off-by: Tadeusz Struk <tadeusz.struk@intel.com>
---
 drivers/char/tpm/tpm-dev-common.c |    8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/char/tpm/tpm-dev-common.c b/drivers/char/tpm/tpm-dev-common.c
index 2ec47a69a2a6..b23b0b999232 100644
--- a/drivers/char/tpm/tpm-dev-common.c
+++ b/drivers/char/tpm/tpm-dev-common.c
@@ -61,6 +61,12 @@ static void tpm_dev_async_work(struct work_struct *work)
 
 	mutex_lock(&priv->buffer_mutex);
 	priv->command_enqueued = false;
+	ret = tpm_try_get_ops(priv->chip);
+	if (ret) {
+		priv->response_length = ret;
+		goto out;
+	}
+
 	ret = tpm_dev_transmit(priv->chip, priv->space, priv->data_buffer,
 			       sizeof(priv->data_buffer));
 	tpm_put_ops(priv->chip);
@@ -68,6 +74,7 @@ static void tpm_dev_async_work(struct work_struct *work)
 		priv->response_length = ret;
 		mod_timer(&priv->user_read_timer, jiffies + (120 * HZ));
 	}
+out:
 	mutex_unlock(&priv->buffer_mutex);
 	wake_up_interruptible(&priv->async_wait);
 }
@@ -204,6 +211,7 @@ ssize_t tpm_common_write(struct file *file, const char __user *buf,
 	if (file->f_flags & O_NONBLOCK) {
 		priv->command_enqueued = true;
 		queue_work(tpm_dev_wq, &priv->async_work);
+		tpm_put_ops(priv->chip);
 		mutex_unlock(&priv->buffer_mutex);
 		return size;
 	}