uprobes: (Re)add missing get_uprobe() in __find_uprobe()

mainline inclusion
from mainline-5.12-rc1
commit b0d6d478
category: bugfix
bugzilla: https://gitee.com/src-openeuler/bpftrace/issues/I5RUM5
CVE: N/A

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=b0d6d4789677d128b1933af023083054f0973574

-------------------------------------------------

commit c6bc9bd06dff ("rbtree, uprobes: Use rbtree helpers")
accidentally removed the refcount increase. Add it again.

Fixes: c6bc9bd06dff ("rbtree, uprobes: Use rbtree helpers")
Signed-off-by: NSven Schnelle <svens@linux.ibm.com>
Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
Link: https://lkml.kernel.org/r/20210209150711.36778-1-svens@linux.ibm.comSigned-off-by: NJason Zeng <jason.zeng@intel.com>

kernel/events/uprobes.c

@@ -663,7 +663,7 @@ static struct uprobe *__find_uprobe(struct inode *inode, loff_t offset)
 	struct rb_node *node = rb_find(&key, &uprobes_tree, __uprobe_cmp_key);
 
 	if (node)
-		return __node_2_uprobe(node);
+		return get_uprobe(__node_2_uprobe(node));
 
 	return NULL;
 }