From: Jan Kara <jack@suse.cz>
Subject: printk: Make wake_up_klogd_work_func() async
Patch-mainline: No, still discussed upstream
References: bnc#744692, bnc#789311

Offload printing of scheduler deferred messages from IRQ context
to a schedulable printing kthread, when possible (the same way we
do it in vprintk_emit()). Otherwise, the CPU can spend unbounded
amount of time doing printing in console_unlock() from IRQ.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/printk.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 64a98ea..89f5441 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2820,9 +2820,16 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work)
 	int pending = __this_cpu_xchg(printk_pending, 0);
 
 	if (pending & PRINTK_PENDING_OUTPUT) {
-		/* If trylock fails, someone else is doing the printing */
-		if (console_trylock())
-			console_unlock();
+		if (printk_kthread) {
+			wake_up_process(printk_kthread);
+		} else {
+			/*
+			 * If trylock fails, someone else is doing
+			 * the printing
+			 */
+			if (console_trylock())
+				console_unlock();
+		}
 	}
 
 	if (pending & PRINTK_PENDING_WAKEUP)
-- 
2.8.0