Re: [PATCH v5 4/6] tee: add tee_dev_open_helper() primitive

On Thu, 26 Aug 2021 at 18:00, Jens Wiklander jens.wiklander@linaro.org wrote:

Adds tee_dev_open_helper() and tee_dev_ctx_put() to make it easier to create a driver internal struct tee_context without the usual tee_device_get() on the struct tee_device as that adds a circular reference counter dependency and would prevent the struct tee_device from ever being released again.

Can you elaborate regarding the circular dependency issue you are referring to? IIUC, lifespan for struct tee_device would look like below with normal teedev_open():

optee_probe() { ... tee_device_alloc() <- teedev->num_users = 1 tee_device_register() optee_notif_init() <- tee_device_get() ... }

optee_remove() { ... optee_notif_uninit() <- tee_device_put() tee_device_unregister() <- tee_device_put() ... }

-Sumit

Signed-off-by: Jens Wiklander jens.wiklander@linaro.org

drivers/tee/tee_core.c | 33 ++++++++++++++++++++++++--------- include/linux/tee_drv.h | 27 +++++++++++++++++++++++++++ 2 files changed, 51 insertions(+), 9 deletions(-)

diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c index 85102d12d716..3beb682684a8 100644 --- a/drivers/tee/tee_core.c +++ b/drivers/tee/tee_core.c @@ -43,14 +43,11 @@ static DEFINE_SPINLOCK(driver_lock); static struct class *tee_class; static dev_t tee_devt;

-static struct tee_context *teedev_open(struct tee_device *teedev) +struct tee_context *tee_dev_open_helper(struct tee_device *teedev) { int rc; struct tee_context *ctx;

•   if (!tee_device_get(teedev))
  

•           return ERR_PTR(-EINVAL);
  

•   ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
    if (!ctx) {
            rc = -ENOMEM;
  

@@ -66,10 +63,30 @@ static struct tee_context *teedev_open(struct tee_device *teedev) return ctx; err: kfree(ctx);

•   tee_device_put(teedev);
    return ERR_PTR(rc);
  
  

} +EXPORT_SYMBOL_GPL(tee_dev_open_helper);

+void tee_dev_ctx_put(struct tee_context *ctx) +{

•   teedev_ctx_put(ctx);
  

+} +EXPORT_SYMBOL_GPL(tee_dev_ctx_put);

+static struct tee_context *teedev_open(struct tee_device *teedev) +{

•   struct tee_context *ctx;
  

•   if (!tee_device_get(teedev))
  

•           return ERR_PTR(-EINVAL);
  

•   ctx = tee_dev_open_helper(teedev);
  

•   if (IS_ERR(ctx))
  

•           tee_device_put(teedev);
  

•   return ctx;
  

+}

void teedev_ctx_get(struct tee_context *ctx) { @@ -90,10 +107,8 @@ static void teedev_ctx_release(struct kref *ref)

void teedev_ctx_put(struct tee_context *ctx) {

•   if (ctx->releasing)
  

•           return;
  

•   kref_put(&ctx->refcount, teedev_ctx_release);
  

•   if (ctx && !ctx->releasing)
  

•           kref_put(&ctx->refcount, teedev_ctx_release);
  

}

static void teedev_close_context(struct tee_context *ctx) diff --git a/include/linux/tee_drv.h b/include/linux/tee_drv.h index 3ebfea0781f1..00a31ff03049 100644 --- a/include/linux/tee_drv.h +++ b/include/linux/tee_drv.h @@ -458,6 +458,33 @@ static inline int tee_shm_get_id(struct tee_shm *shm) */ struct tee_shm *tee_shm_get_from_id(struct tee_context *ctx, int id);

+/**

• • tee_dev_open_helper() - helper function to make a struct tee_context
• • @teedev: Device to open
• • Creates the struct tee_context without increasing the reference counter
• • on @teedev. This is needed for instance when a driver need an internal
• • struct tee_context to operate on. By skipping the reference counter
• • the circular dependency is broken.
• • Note that this struct tee_context need special care when freeing in
• • order to avoid the normal put on the struct tee_device.
• • tee_dev_ctx_put() is the best choice for this.
• • @returns a pointer 'struct tee_context' on success or an ERR_PTR on failure
• */

+struct tee_context *tee_dev_open_helper(struct tee_device *teedev);

+/**

• • tee_dev_ctx_put() - helper function to release a struct tee_context
• • @ctx: The struct tee_context to release
• • Note that this function doesn't do a tee_device_put() on the internal
• • struct tee_device so this function should normal only be used when
• • releasing a struct tee_context obtained with tee_dev_open_helper().
• */

+void tee_dev_ctx_put(struct tee_context *ctx);

/**

• tee_client_open_context() - Open a TEE context
• @start: if not NULL, continue search after this context

-- 2.31.1