[PATCH v3 4/9] pseries/papr-hvpipe: Fix & simplify error handling in papr_hvpipe_init()

[Ritesh Harjani (IBM)]

Remove such 3 levels of nesting patterns to check success return values
from function calls.

ret = enable_hvpipe_IRQ()
    if (!ret)
	    ret = set_hvpipe_sys_param(1)
	        if (!ret)
		    ret = misc_register()

Instead just bail out to "out*:" labels, in case of any error. This
simplifies the init flow.

While at it let's also fix the following error handling logic:
We have already enabled interrupt sources and enabled hvpipe to received
interrupts, if misc_register() fails, we will destroy the workqueue, but
the HMC might send us a msg via hvpipe which will call, queue work on
the workqueue which might be destroyed.

So instead, let's reverse the order of enabling set_hvpipe_sys_param(1)
and in case of an error let's remove the misc dev by calling
misc_deregister().

Cc: stable@xxxxxxxxxxxxxxx
Fixes: 39a08a4f94980 ("powerpc/pseries: Enable hvpipe with ibm,set-system-parameter RTAS")
Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx>
---
 arch/powerpc/platforms/pseries/papr-hvpipe.c | 28 ++++++++++++--------
 1 file changed, 17 insertions(+), 11 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/papr-hvpipe.c b/arch/powerpc/platforms/pseries/papr-hvpipe.c
index 402781299497..800649f309a5 100644
--- a/arch/powerpc/platforms/pseries/papr-hvpipe.c
+++ b/arch/powerpc/platforms/pseries/papr-hvpipe.c
@@ -780,23 +780,29 @@ static int __init papr_hvpipe_init(void)
 	}
 
 	ret = enable_hvpipe_IRQ();
-	if (!ret) {
-		ret = set_hvpipe_sys_param(1);
-		if (!ret)
-			ret = misc_register(&papr_hvpipe_dev);
-	}
+	if (ret)
+		goto out_wq;
 
-	if (!ret) {
-		pr_info("hvpipe feature is enabled\n");
-		hvpipe_feature = true;
-		return 0;
-	}
+	ret = misc_register(&papr_hvpipe_dev);
+	if (ret)
+		goto out_wq;
 
-	pr_err("hvpipe feature is not enabled %d\n", ret);
+	ret = set_hvpipe_sys_param(1);
+	if (ret)
+		goto out_misc;
+
+	pr_info("hvpipe feature is enabled\n");
+	hvpipe_feature = true;
+	return 0;
+
+out_misc:
+	misc_deregister(&papr_hvpipe_dev);
+out_wq:
 	destroy_workqueue(papr_hvpipe_wq);
 out:
 	kfree(papr_hvpipe_work);
 	papr_hvpipe_work = NULL;
+	pr_err("hvpipe feature is not enabled %d\n", ret);
 	return ret;
 }
 machine_device_initcall(pseries, papr_hvpipe_init);
-- 
2.39.5