linux-kernel - [PATCH v7 04/10] tpm: Get rid of module locking

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Message-Id: <1457751065-11507-5-git-send-email-stefanb@linux.vnet.ibm.com>
Date:	Fri, 11 Mar 2016 21:50:59 -0500
From:	Stefan Berger <stefanb@...ux.vnet.ibm.com>
To:	tpmdd-devel@...ts.sourceforge.net
Cc:	jarkko.sakkinen@...ux.intel.com, jgunthorpe@...idianresearch.com,
	linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Stefan Berger <stefanb@...ux.vnet.ibm.com>
Subject: [PATCH v7 04/10] tpm: Get rid of module locking

Now that the tpm core has strong locking around 'ops' it is possible
to remove a TPM driver, module and all, even while user space still
has things like /dev/tpmX open. For consistency and simplicity, drop
the module locking entirely.

The module lock can be dropped since /dev/tpmX holds the reader lock
on 'ops' while using 'ops' and this prevents the module from un-
registering, which needs the writer lock. Once the module unregistered
the 'ops' cannot be found anymore.

Signed-off-by: Stefan Berger <stefanb@...ux.vnet.ibm.com>
Reviewed-by: Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
---
 drivers/char/tpm/tpm-chip.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c
index 5793ea1..6636728 100644
--- a/drivers/char/tpm/tpm-chip.c
+++ b/drivers/char/tpm/tpm-chip.c
@@ -57,9 +57,6 @@ int tpm_try_get_ops(struct tpm_chip *chip)
 	if (!chip->ops)
 		goto out_lock;
 
-	if (!try_module_get(chip->dev.parent->driver->owner))
-		goto out_lock;
-
 	return 0;
 out_lock:
 	up_read(&chip->ops_sem);
@@ -77,7 +74,6 @@ EXPORT_SYMBOL_GPL(tpm_try_get_ops);
  */
 void tpm_put_ops(struct tpm_chip *chip)
 {
-	module_put(chip->dev.parent->driver->owner);
 	up_read(&chip->ops_sem);
 	put_device(&chip->dev);
 }
@@ -183,7 +179,7 @@ struct tpm_chip *tpmm_chip_alloc(struct device *dev,
 		goto out;
 
 	cdev_init(&chip->cdev, &tpm_fops);
-	chip->cdev.owner = dev->driver->owner;
+	chip->cdev.owner = THIS_MODULE;
 	chip->cdev.kobj.parent = &chip->dev.kobj;
 
 	rc = devm_add_action(dev, (void (*)(void *)) put_device, &chip->dev);
-- 
2.4.3