irqdomain: Prevent potential NULL pointer dereference in irq_domain_push_irq()

This code generates a Smatch warning:

  kernel/irq/irqdomain.c:1511 irq_domain_push_irq()
  warn: variable dereferenced before check 'root_irq_data' (see line 1508)

irq_get_irq_data() can return a NULL pointer, but the code dereferences
the returned pointer before checking it.

Move the NULL pointer check before the dereference.

[ tglx: Rewrote changelog to be precise and conforming to the instructions
  	in submitting-patches and added a Fixes tag. Sigh! ]

Fixes: 495c38d3001f ("irqdomain: Add irq_domain_{push,pop}_irq() functions")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: David Daney <david.daney@cavium.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: kernel-janitors@vger.kernel.org
Link: http://lkml.kernel.org/r/20170825121409.6rfv4vt6ztz2oqkt@mwanda

1 files changed, 2 insertions, 2 deletions

diff --git a/kernel/irq/irqdomain.c b/kernel/irq/irqdomain.c
index 1ff9912211e9..d62351714f3e 100644
--- a/kernel/irq/irqdomain.c
+++ b/kernel/irq/irqdomain.c
@@ -1504,10 +1504,10 @@ int irq_domain_push_irq(struct irq_domain *domain, int virq, void *arg)
         if (WARN_ON(!irq_domain_is_hierarchy(domain)))
                 return -EINVAL;
 
-        if (domain->parent != root_irq_data->domain)
+        if (!root_irq_data)
                 return -EINVAL;
 
-        if (!root_irq_data)
+        if (domain->parent != root_irq_data->domain)
                 return -EINVAL;
 
         child_irq_data = kzalloc_node(sizeof(*child_irq_data), GFP_KERNEL,