Re: [PROBLEM]: WARNING: lock held when returning to user space! (5.4.1 #16 Tainted: G )

Jarkko Sakkinen
2019-12-11T17:45:44Z

On Mon, Dec 09, 2019 at 01:34:29PM -0800, Tadeusz Struk wrote:
> I think that's expected for a non-blocking operation.

What do you mean by "expected"?

It is a locking bug. When you implemented the feature you failed
to free locks before going back to the user space and I failed to
notice this when I reviewed the code.

> To get rid of the warning it should be changed to something like this:
>
> diff --git a/drivers/char/tpm/tpm-dev-common.c
> b/drivers/char/tpm/tpm-dev-common.c
> index 2ec47a69a2a6..47f1c0c5c8de 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);
> }
> @@ -205,6 +212,7 @@ ssize_t tpm_common_write(struct file *file, const
> char __user *buf,
> priv->command_enqueued = true;
> queue_work(tpm_dev_wq, &priv->async_work);
> mutex_unlock(&priv->buffer_mutex);
> + tpm_put_ops(priv->chip);
> return size;
> }
>
>
>
> --
> Tadeusz

The fix looks appropriate but needs to be formalized as a patch.

/Jarkko