[PATCH v2 1/2] livepatch: Remove duplicate warning about missing reliable stacktrace support

[Petr Mladek <pmladek@suse.com>]

WARN_ON_ONCE() could not be called safely under rq lock because
of console deadlock issues. Fortunately, there is another check
for the reliable stacktrace support in klp_enable_patch().

Signed-off-by: Petr Mladek <pmladek@suse.com>
---
 kernel/livepatch/transition.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 9c89ae8b337a..8e0274075e75 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -263,8 +263,15 @@ static int klp_check_stack(struct task_struct *task, char *err_buf)
 	trace.nr_entries = 0;
 	trace.max_entries = MAX_STACK_ENTRIES;
 	trace.entries = entries;
+
 	ret = save_stack_trace_tsk_reliable(task, &trace);
-	WARN_ON_ONCE(ret == -ENOSYS);
+	/*
+	 * pr_warn() under task rq lock might cause a deadlock.
+	 * Fortunately, missing reliable stacktrace support has
+	 * already been handled when the livepatch was enabled.
+	 */
+	if (ret == -ENOSYS)
+		return ret;
 	if (ret) {
 		snprintf(err_buf, STACK_ERR_BUF_SIZE,
 			 "%s: %s:%d has an unreliable stack\n",
-- 
2.16.4