linux-kernel - Re: [PATCH 1/4] TPM: update char dev BKL pushdown

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Message-ID: <20080923145807.63f9b904@bike.lwn.net>
Date:	Tue, 23 Sep 2008 14:58:07 -0600
From:	Jonathan Corbet <corbet@....net>
To:	Rajiv Andrade <srajiv@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	jmoriss@...ei.org, serue@...ux.vnet.ibm.com,
	zohar@...ux.vnet.ibm.com, safford@...son.ibm.com,
	paulmck@...ux.vnet.ibm.com, debora@...ux.vnet.ibm.com
Subject: Re: [PATCH 1/4] TPM: update char dev BKL pushdown

On Tue, 23 Sep 2008 14:19:26 -0300
Rajiv Andrade <srajiv@...ux.vnet.ibm.com> wrote:

> + * It's assured that the chip will be opened just once,
> + * by the check of is_open variable, which is protected
> + * by driver_lock.

Taking a look at the code, I'm convinced.  BKL removal seems
appropriate.

While I was in the neighborhood, though, something caught my eye:

int tpm_release(struct inode *inode, struct file *file)
{
	struct tpm_chip *chip = file->private_data;

	flush_scheduled_work();

Here you have waited until you've got nothing in the workqueue.

	spin_lock(&driver_lock);
	file->private_data = NULL;
	del_singleshot_timer_sync(&chip->user_read_timer);

But, until you get here, your timer could have resubmitted a job into
the workqueue - job which could run after you've freed "chip" and
forgotten all about it. I think you need either a "don't resubmit" flag,
or you need to delete the timer first.

jon
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