[PATCH] relay: replay_file_open(): NULL ptr deref in CPU hotplugs

["Yichun Zhang (agentzh)" <yichun@xxxxxxxxxxxxx>]

CPU hotplug may introduce race conditions. We reproduced kernel panics
due to this NULL ptr deref error when doing frequent random CPU hotplugs
in a KVM guest.

Signed-off-by: Yichun Zhang (agentzh) <yichun@xxxxxxxxxxxxx>
---
 kernel/relay.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/relay.c b/kernel/relay.c
index 6a611e779e95..2db69fd527d1 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -816,6 +816,9 @@ EXPORT_SYMBOL_GPL(relay_flush);
 static int relay_file_open(struct inode *inode, struct file *filp)
 {
 	struct rchan_buf *buf = inode->i_private;
+	if (unlikely(buf == NULL))
+		return -ENOENT;
+
 	kref_get(&buf->kref);
 	filp->private_data = buf;
 
-- 
2.17.2