tee: optee: Fix supplicant wait loop

OP-TEE supplicant is a user-space daemon and it's possible for it
be 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 indefinitely waiting in an unkillable state. Also,
a normal uninterruptible wait should not have resulted in the hung-task
watchdog getting triggered, but the endless loop would.

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: 4fb0a5e ("tee: add OP-TEE driver")
Suggested-by: Arnd Bergmann <[email protected]>
Cc: [email protected]
Signed-off-by: Sumit Garg <[email protected]>
Reviewed-by: Arnd Bergmann <[email protected]>
Reviewed-by: Jens Wiklander <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>

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 +110,18 @@ 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)) {
+	if (wait_for_completion_killable(&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 (req->in_queue) {
-				list_del(&req->link);
-				req->in_queue = false;
-			}
+		if (req->in_queue) {
+			list_del(&req->link);
+			req->in_queue = false;
 		}
 		mutex_unlock(&supp->mutex);
-
-		if (interruptable) {
-			req->ret = TEEC_ERROR_COMMUNICATION;
-			break;
-		}
+		req->ret = TEEC_ERROR_COMMUNICATION;
 	}
 
 	ret = req->ret;