linux-kernel - Re: [PATCH v3 RESEND 2/2] tpm: add support for nonblocking operation

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Date:   Tue, 7 Aug 2018 12:20:13 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
Cc:     Tadeusz Struk <tadeusz.struk@...el.com>,
        jarkko.sakkinen@...ux.intel.com, flihp@...bit.us,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 RESEND 2/2] tpm: add support for nonblocking operation

On Mon, Aug 06, 2018 at 04:05:48PM -0700, James Bottomley wrote:

> > @@ -118,25 +155,48 @@ ssize_t tpm_common_write(struct file *file,
> > const char __user *buf,
> >  	 * the char dev is held open.
> >  	 */
> >  	if (tpm_try_get_ops(priv->chip)) {
> > -		mutex_unlock(&priv->buffer_mutex);
> > -		return -EPIPE;
> > +		ret = -EPIPE;
> > +		goto out;
> >  	}
> > -	out_size = tpm_transmit(priv->chip, priv->space, priv-
> > >data_buffer,
> > -				sizeof(priv->data_buffer), 0);
> >  
> > -	tpm_put_ops(priv->chip);
> > -	if (out_size < 0) {
> > -		mutex_unlock(&priv->buffer_mutex);
> > -		return out_size;
> > +	/*
> > +	 * If in nonblocking mode schedule an async job to send
> > +	 * the command return the size.
> > +	 * In case of error the err code will be returned in
> > +	 * the subsequent read call.
> > +	 */
> > +	if (file->f_flags & O_NONBLOCK) {
> > +		queue_work(tpm_dev_wq, &priv->async_work);
> > +		return size;
> 
> Here you return holding the buffer_mutex, waiting for tpm_async_work to
> release it.

Doesn't lockdep complain when locks are left held after returning to
user space? Even if it doesn't, that is a pretty ugly thing to do.

Jason