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SubjectRe: [PATCH] TPM: update char dev BKL pushdown
Quoting Rajiv Andrade (srajiv@linux.vnet.ibm.com):
> This patch removes the BKL calls from the TPM driver, which
> were added in the overall misc-char-dev-BKL-pushdown.patch,
> as they are not needed. Changed num_opens from an int to atomic_t.
>
> Signed-off-by: Mimi Zohar <zohar@us.ibm.com>
> Signed-off-by: Rajiv Andrade <srajiv@linux.vnet.ibm.com>

Yes, this patch is good.

It would also be good to rename num_opens. Note that it is always
either 0 or 1, and indicates whether someone has opened the chip.
So 'is_open' may make more sense.

Mimi is also working on a patch (on top of this one) to use rcu
to protect chip->list, and that patch will (I hope) include an
explanation of all of the locking/protection involved.

Acked-by: Serge Hallyn <serue@us.ibm.com>

> ---
> drivers/char/tpm/tpm.c | 22 +++++++---------------
> drivers/char/tpm/tpm.h | 2 +-
> 2 files changed, 8 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/char/tpm/tpm.c b/drivers/char/tpm/tpm.c
> index ae766d8..cd4ff36 100644
> --- a/drivers/char/tpm/tpm.c
> +++ b/drivers/char/tpm/tpm.c
> @@ -960,7 +960,6 @@ 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 +974,31 @@ int tpm_open(struct inode *inode, struct file *file)
> goto err_out;
> }
>
> - if (chip->num_opens) {
> + if (atomic_read(&chip->num_opens)) {
> dev_dbg(chip->dev, "Another process owns this TPM\n");
> rc = -EBUSY;
> goto err_out;
> }
>
> - chip->num_opens++;
> + atomic_inc(&chip->num_opens);
> get_device(chip->dev);
>
> spin_unlock(&driver_lock);
>
> chip->data_buffer = kmalloc(TPM_BUFSIZE * sizeof(u8), GFP_KERNEL);
> if (chip->data_buffer == NULL) {
> - chip->num_opens--;
> + atomic_dec(&chip->num_opens);
> 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 +1012,7 @@ 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_dec(chip->num_opens);
> put_device(chip->dev);
> kfree(chip->data_buffer);
> spin_unlock(&driver_lock);
> @@ -1231,20 +1227,16 @@ 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..edb8ed6 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 num_opens; /* 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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