linux-kernel - [PATCH][resubmit] TPM: update char dev BKL pushdown

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Date:	Tue, 26 Aug 2008 17:56:25 -0300
From:	Rajiv Andrade <srajiv@...ux.vnet.ibm.com>
To:	linux-kernel@...r.kernel.org
Cc:	zohar@...ibm.com, dvelarde@...ibm.com, serue@...ibm.com,
	safford@...ibm.com
Subject: [PATCH][resubmit] TPM: update char dev BKL pushdown

Now considering the num_opens to is_open change and the use of atomic_set
instead of atomic_dec and atomic_inc. This also includes additional comments on
tpm_open.

Signed-off-by: Mimi Zohar <zohar@...ibm.com>
Signed-off-by: Rajiv Andrade <srajiv@...ux.vnet.ibm.com>

---
 drivers/char/tpm/tpm.c |   35 ++++++++++++++++++-----------------
 drivers/char/tpm/tpm.h |    2 +-
 2 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
index ae766d8..09829f3 100644
--- a/drivers/char/tpm/tpm.c
+++ b/drivers/char/tpm/tpm.c
@@ -954,13 +954,16 @@ EXPORT_SYMBOL_GPL(tpm_store_cancel);
 
 /*
  * Device file system interface to the TPM
+ *
+ * It's assured that the chip will be opened just once,
+ * by the check of is_open variable, which is protected
+ * by driver_lock.
  */
 int tpm_open(struct inode *inode, struct file *file)
 {
 	int rc = 0, minor = iminor(inode);
 	struct tpm_chip *chip = NULL, *pos;
 
-	lock_kernel();
 	spin_lock(&driver_lock);
 
 	list_for_each_entry(pos, &tpm_chip_list, list) {
@@ -975,34 +978,31 @@ int tpm_open(struct inode *inode, struct file *file)
 		goto err_out;
 	}
 
-	if (chip->num_opens) {
+	if (atomic_read(&chip->is_open)) {
 		dev_dbg(chip->dev, "Another process owns this TPM\n");
 		rc = -EBUSY;
 		goto err_out;
 	}
 
-	chip->num_opens++;
-	get_device(chip->dev);
+	atomic_set(&chip->is_open, 1);
+	get_device(chip->dev); /* protect from chip disappearing */
 
 	spin_unlock(&driver_lock);
 
 	chip->data_buffer = kmalloc(TPM_BUFSIZE * sizeof(u8), GFP_KERNEL);
 	if (chip->data_buffer == NULL) {
-		chip->num_opens--;
+		atomic_set(&chip->is_open, 0);
 		put_device(chip->dev);
-		unlock_kernel();
 		return -ENOMEM;
 	}
 
 	atomic_set(&chip->data_pending, 0);
 
 	file->private_data = chip;
-	unlock_kernel();
 	return 0;
 
 err_out:
 	spin_unlock(&driver_lock);
-	unlock_kernel();
 	return rc;
 }
 EXPORT_SYMBOL_GPL(tpm_open);
@@ -1016,7 +1016,7 @@ int tpm_release(struct inode *inode, struct file *file)
 	file->private_data = NULL;
 	del_singleshot_timer_sync(&chip->user_read_timer);
 	atomic_set(&chip->data_pending, 0);
-	chip->num_opens--;
+	atomic_set(&chip->is_open, 0);
 	put_device(chip->dev);
 	kfree(chip->data_buffer);
 	spin_unlock(&driver_lock);
@@ -1082,7 +1082,12 @@ ssize_t tpm_read(struct file *file, char __user *buf,
 	return ret_size;
 }
 EXPORT_SYMBOL_GPL(tpm_read);
-
+/*
+ *   Called on unloading the driver.
+ *
+ *   First part unloading the chip is done here. The remainder
+ *   is done, when the device count reaches 0, in tpm_dev_release().
+ */
 void tpm_remove_hardware(struct device *dev)
 {
 	struct tpm_chip *chip = dev_get_drvdata(dev);
@@ -1231,20 +1236,16 @@ struct tpm_chip *tpm_register_hardware(struct device *dev, const struct tpm_vend
 		return NULL;
 	}
 
-	spin_lock(&driver_lock);
-
-	list_add(&chip->list, &tpm_chip_list);
-
-	spin_unlock(&driver_lock);
-
 	if (sysfs_create_group(&dev->kobj, chip->vendor.attr_group)) {
-		list_del(&chip->list);
 		misc_deregister(&chip->vendor.miscdev);
 		put_device(chip->dev);
 		return NULL;
 	}
 
 	chip->bios_dir = tpm_bios_log_setup(devname);
+	spin_lock(&driver_lock);
+	list_add(&chip->list, &tpm_chip_list);
+	spin_unlock(&driver_lock);
 
 	return chip;
 }
diff --git a/drivers/char/tpm/tpm.h b/drivers/char/tpm/tpm.h
index e885148..7e0d3fb 100644
--- a/drivers/char/tpm/tpm.h
+++ b/drivers/char/tpm/tpm.h
@@ -90,7 +90,7 @@ struct tpm_chip {
 	struct device *dev;	/* Device stuff */
 
 	int dev_num;		/* /dev/tpm# */
-	int num_opens;		/* only one allowed */
+	atomic_t is_open;	/* only one allowed */
 	int time_expired;
 
 	/* Data passed to and from the tpm via the read/write calls */
-- 
1.5.4.5



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