[PATCH] printk: Don't WARN on kthread_run failure.

[Tetsuo Handa]

Since __kthread_create_on_node() returns -EINTR upon SIGKILL,
we should not use WARN_ON() in order to catch kthread_run() failure.

Reported-by: syzbot+1ebbc20f223b99446034@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://syzkaller.appspot.com/bug?extid=1ebbc20f223b99446034
Fixes: 5f53ca3ff83b ("printk: Implement legacy printer kthread for PREEMPT_RT")
Fixes: 76f258bf3f2a ("printk: nbcon: Introduce printer kthreads")
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
 kernel/printk/nbcon.c  | 2 +-
 kernel/printk/printk.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/nbcon.c b/kernel/printk/nbcon.c
index 4b03b019cd5e..a5921a84a80e 100644
--- a/kernel/printk/nbcon.c
+++ b/kernel/printk/nbcon.c
@@ -1382,7 +1382,7 @@ bool nbcon_kthread_create(struct console *con)
 		return true;
 
 	kt = kthread_run(nbcon_kthread_func, con, "pr/%s%d", con->name, con->index);
-	if (WARN_ON(IS_ERR(kt))) {
+	if (IS_ERR(kt)) {
 		con_printk(KERN_ERR, con, "failed to start printing thread\n");
 		return false;
 	}
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 2fe9a963c823..cf15ed75fd26 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -3725,7 +3725,7 @@ static bool legacy_kthread_create(void)
 	lockdep_assert_console_list_lock_held();
 
 	kt = kthread_run(legacy_kthread_func, NULL, "pr/legacy");
-	if (WARN_ON(IS_ERR(kt))) {
+	if (IS_ERR(kt)) {
 		pr_err("failed to start legacy printing thread\n");
 		return false;
 	}
-- 
2.52.0