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Message-ID: <CAHUa44FWM-QRfeEb5rreN4J9yJjQJQrh3XEm-YLBQmZMvBLC0g@mail.gmail.com>
Date: Fri, 27 Aug 2021 11:26:16 +0200
From: Jens Wiklander <jens.wiklander@...aro.org>
To: Sumit Garg <sumit.garg@...aro.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
OP-TEE TrustedFirmware <op-tee@...ts.trustedfirmware.org>,
Devicetree List <devicetree@...r.kernel.org>,
Linux Doc Mailing List <linux-doc@...r.kernel.org>,
Jerome Forissier <jerome@...issier.org>,
Etienne Carriere <etienne.carriere@...aro.org>,
Vincent Guittot <vincent.guittot@...aro.org>,
Rob Herring <robh+dt@...nel.org>,
Jonathan Corbet <corbet@....net>,
Ard Biesheuvel <ardb@...nel.org>, Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH v5 4/6] tee: add tee_dev_open_helper() primitive
On Fri, Aug 27, 2021 at 8:23 AM Sumit Garg <sumit.garg@...aro.org> wrote:
>
> On Thu, 26 Aug 2021 at 18:00, Jens Wiklander <jens.wiklander@...aro.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()
> ...
> }
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
>
> >
> > Signed-off-by: Jens Wiklander <jens.wiklander@...aro.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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