cxl: Fix leaking pid refs in some error paths

In some error paths in functions cxl_start_context and
afu_ioctl_start_work pid references to the current & group-leader tasks
can leak after they are taken. This patch fixes these error paths to
release these pid references before exiting the error path.

Fixes: 7b8ad49 ("cxl: Fix DSI misses when the context owning task exits")
Cc: stable@vger.kernel.org # v4.5+
Reviewed-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Reported-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Vaibhav Jain <vaibhav@linux.vnet.ibm.com>
Acked-by: Frederic Barrat <fbarrat@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/api.c

@@ -247,7 +247,9 @@ int cxl_start_context(struct cxl_context *ctx, u64 wed,
 	cxl_ctx_get();
 
 	if ((rc = cxl_ops->attach_process(ctx, kernel, wed, 0))) {
+		put_pid(ctx->glpid);
 		put_pid(ctx->pid);
+		ctx->glpid = ctx->pid = NULL;
 		cxl_adapter_context_put(ctx->afu->adapter);
 		cxl_ctx_put();
 		goto out;

drivers/misc/cxl/file.c

@@ -193,6 +193,16 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
 
 	ctx->mmio_err_ff = !!(work.flags & CXL_START_WORK_ERR_FF);
 
+	/*
+	 * Increment the mapped context count for adapter. This also checks
+	 * if adapter_context_lock is taken.
+	 */
+	rc = cxl_adapter_context_get(ctx->afu->adapter);
+	if (rc) {
+		afu_release_irqs(ctx, ctx);
+		goto out;
+	}
+
 	/*
 	 * We grab the PID here and not in the file open to allow for the case
 	 * where a process (master, some daemon, etc) has opened the chardev on
@@ -205,22 +215,16 @@ static long afu_ioctl_start_work(struct cxl_context *ctx,
 	ctx->pid = get_task_pid(current, PIDTYPE_PID);
 	ctx->glpid = get_task_pid(current->group_leader, PIDTYPE_PID);
 
-	/*
-	 * Increment the mapped context count for adapter. This also checks
-	 * if adapter_context_lock is taken.
-	 */
-	rc = cxl_adapter_context_get(ctx->afu->adapter);
-	if (rc) {
-		afu_release_irqs(ctx, ctx);
-		goto out;
-	}
 
 	trace_cxl_attach(ctx, work.work_element_descriptor, work.num_interrupts, amr);
 
 	if ((rc = cxl_ops->attach_process(ctx, false, work.work_element_descriptor,
 							amr))) {
 		afu_release_irqs(ctx, ctx);
 		cxl_adapter_context_put(ctx->afu->adapter);
+		put_pid(ctx->glpid);
+		put_pid(ctx->pid);
+		ctx->glpid = ctx->pid = NULL;
 		goto out;
 	}