[PATCH 3/5][resubmit] TPM: rcu locking

[Rajiv Andrade <srajiv@linux.vnet.ibm.com>]

This is a resubmission of rcu locking patch, posted some hours ago, addressing Serge Hallyn's comment.
In the previous patch there was missing the spin_lock/unlock protecting list_add_rcu() 
in tpm_register_hardware(). There were also an unnecessary list_del() inside the same function, 
that is now being removed.

Signed-off-by: Mimi Zohar <zohar@linux.vnet.ibm.com>
Signed-off-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>
---
 drivers/char/tpm/tpm.c |   61 +++++++++++++++++++-----------------------------
 1 files changed, 24 insertions(+), 37 deletions(-)

diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
index dfd4e7f..e96ca5a 100644
--- a/drivers/char/tpm/tpm.c
+++ b/drivers/char/tpm/tpm.c
@@ -961,33 +961,28 @@ EXPORT_SYMBOL_GPL(tpm_store_cancel);
  */
 int tpm_open(struct inode *inode, struct file *file)
 {
-	int rc = 0, minor = iminor(inode);
+	int minor = iminor(inode);
 	struct tpm_chip *chip = NULL, *pos;
 
-	spin_lock(&driver_lock);
-
-	list_for_each_entry(pos, &tpm_chip_list, list) {
+	rcu_read_lock();
+	list_for_each_entry_rcu(pos, &tpm_chip_list, list) {
 		if (pos->vendor.miscdev.minor == minor) {
 			chip = pos;
+			get_device(chip->dev);
 			break;
 		}
 	}
+	rcu_read_unlock();
 
-	if (chip == NULL) {
-		rc = -ENODEV;
-		goto err_out;
-	}
+	if (!chip)
+		return -ENODEV;
 
 	if (test_and_set_bit(0, &chip->is_open)) {
 		dev_dbg(chip->dev, "Another process owns this TPM\n");
-		rc = -EBUSY;
-		goto err_out;
+		put_device(chip->dev);
+		return -EBUSY;
 	}
 
-	get_device(chip->dev);
-
-	spin_unlock(&driver_lock);
-
 	chip->data_buffer = kmalloc(TPM_BUFSIZE * sizeof(u8), GFP_KERNEL);
 	if (chip->data_buffer == NULL) {
 		clear_bit(0, &chip->is_open);
@@ -999,26 +994,23 @@ int tpm_open(struct inode *inode, struct file *file)
 
 	file->private_data = chip;
 	return 0;
-
-err_out:
-	spin_unlock(&driver_lock);
-	return rc;
 }
 EXPORT_SYMBOL_GPL(tpm_open);
 
+/*
+ * Called on file close
+ */
 int tpm_release(struct inode *inode, struct file *file)
 {
 	struct tpm_chip *chip = file->private_data;
 
 	flush_scheduled_work();
-	spin_lock(&driver_lock);
 	file->private_data = NULL;
 	del_singleshot_timer_sync(&chip->user_read_timer);
 	atomic_set(&chip->data_pending, 0);
+	kfree(chip->data_buffer);
 	clear_bit(0, &chip->is_open);
 	put_device(chip->dev);
-	kfree(chip->data_buffer);
-	spin_unlock(&driver_lock);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(tpm_release);
@@ -1092,13 +1084,11 @@ void tpm_remove_hardware(struct device *dev)
 	}
 
 	spin_lock(&driver_lock);
-
-	list_del(&chip->list);
-
+	list_del_rcu(&chip->list);
 	spin_unlock(&driver_lock);
+	synchronize_rcu();
 
 	misc_deregister(&chip->vendor.miscdev);
-
 	sysfs_remove_group(&dev->kobj, chip->vendor.attr_group);
 	tpm_bios_log_teardown(chip->bios_dir);
 
@@ -1146,8 +1136,7 @@ EXPORT_SYMBOL_GPL(tpm_pm_resume);
 /*
  * Once all references to platform device are down to 0,
  * release all allocated structures.
- * In case vendor provided release function,
- * call it too.
+ * In case vendor provided release function, call it too.
  */
 static void tpm_dev_release(struct device *dev)
 {
@@ -1155,7 +1144,6 @@ static void tpm_dev_release(struct device *dev)
 
 	if (chip->vendor.release)
 		chip->vendor.release(dev);
-
 	chip->release(dev);
 
 	clear_bit(chip->dev_num, dev_mask);
@@ -1170,8 +1158,8 @@ static void tpm_dev_release(struct device *dev)
  * upon errant exit from this function specific probe function should call
  * pci_disable_device
  */
-struct tpm_chip *tpm_register_hardware(struct device *dev, const struct tpm_vendor_specific
-				       *entry)
+struct tpm_chip *tpm_register_hardware(struct device *dev,
+					const struct tpm_vendor_specific *entry)
 {
 #define DEVNAME_SIZE 7
 
@@ -1230,21 +1218,20 @@ 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);
 
+	/* Make chip available */
+	spin_lock(&driver_lock);
+	list_add_rcu(&chip->list, &tpm_chip_list);
+	spin_lock(&driver_lock);
+
 	return chip;
 }
 EXPORT_SYMBOL_GPL(tpm_register_hardware);
-- 
1.5.6.3