On Fri, Aug 27, 2021 at 8:23 AM Sumit Garg [off-list ref] wrote:

On Thu, 26 Aug 2021 at 18:00, Jens Wiklander [off-list ref] wrote:

quoted

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()
  ...
}

You're right, it works just as well without this patch.
teedev_close_context() and teedev_open() must be exported in another
patch though. I'll replace this patch with such a patch in the next
patch set.


Thanks,
Jens

-Sumit

quoted

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

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