[PATCH v2] tee: optee: Fix supplicant wait loop

[Sumit Garg <sumit.garg@linaro.org>]

OP-TEE supplicant is a user-space daemon and it's possible for it
being hung or crashed or killed in the middle of processing an OP-TEE
RPC call. It becomes more complicated when there is incorrect shutdown
ordering of the supplicant process vs the OP-TEE client application which
can eventually lead to system hang-up waiting for the closure of the
client application.

Allow the client process waiting in kernel for supplicant response to
be killed rather than indefinitetly waiting in an unkillable state. This
fixes issues observed during system reboot/shutdown when supplicant got
hung for some reason or gets crashed/killed which lead to client getting
hung in an unkillable state. It in turn lead to system being in hung up
state requiring hard power off/on to recover.

Fixes: 4fb0a5eb364d ("tee: add OP-TEE driver")
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>
---

Changes in v2:
- Switch to killable wait instead as suggested by Arnd instead
  of supplicant timeout. It atleast allow the client to wait for
  supplicant in killable state which in turn allows system to reboot
  or shutdown gracefully.

 drivers/tee/optee/supp.c | 32 +++++++-------------------------
 1 file changed, 7 insertions(+), 25 deletions(-)

diff --git a/drivers/tee/optee/supp.c b/drivers/tee/optee/supp.c
index 322a543b8c27..3fbfa9751931 100644
--- a/drivers/tee/optee/supp.c
+++ b/drivers/tee/optee/supp.c
@@ -80,7 +80,6 @@ u32 optee_supp_thrd_req(struct tee_context *ctx, u32 func, size_t num_params,
 	struct optee *optee = tee_get_drvdata(ctx->teedev);
 	struct optee_supp *supp = &optee->supp;
 	struct optee_supp_req *req;
-	bool interruptable;
 	u32 ret;
 
 	/*
@@ -111,36 +110,19 @@ u32 optee_supp_thrd_req(struct tee_context *ctx, u32 func, size_t num_params,
 	/*
 	 * Wait for supplicant to process and return result, once we've
 	 * returned from wait_for_completion(&req->c) successfully we have
-	 * exclusive access again.
+	 * exclusive access again. Allow the wait to be killable such that
+	 * the wait doesn't turn into an indefinite state if the supplicant
+	 * gets hung for some reason.
 	 */
-	while (wait_for_completion_interruptible(&req->c)) {
-		mutex_lock(&supp->mutex);
-		interruptable = !supp->ctx;
-		if (interruptable) {
-			/*
-			 * There's no supplicant available and since the
-			 * supp->mutex currently is held none can
-			 * become available until the mutex released
-			 * again.
-			 *
-			 * Interrupting an RPC to supplicant is only
-			 * allowed as a way of slightly improving the user
-			 * experience in case the supplicant hasn't been
-			 * started yet. During normal operation the supplicant
-			 * will serve all requests in a timely manner and
-			 * interrupting then wouldn't make sense.
-			 */
+	if (wait_for_completion_killable(&req->c)) {
+		if (!mutex_lock_killable(&supp->mutex))	{
 			if (req->in_queue) {
 				list_del(&req->link);
 				req->in_queue = false;
 			}
+			mutex_unlock(&supp->mutex);
 		}
-		mutex_unlock(&supp->mutex);
-
-		if (interruptable) {
-			req->ret = TEEC_ERROR_COMMUNICATION;
-			break;
-		}
+		req->ret = TEEC_ERROR_COMMUNICATION;
 	}
 
 	ret = req->ret;
-- 
2.43.0