[RFC][PATCH 2/4] printk: offload printing from wake_up_klogd_work_func()

[Sergey Senozhatsky]

Offload printing of printk_deferred() messages from IRQ context
to a schedulable printing kthread, when possible (the same way
we do it in vprintk_emit()). Otherwise, console_unlock() can
force the printing CPU to spend unbound amount of time flushing
kernel messages from IRQ context.

Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.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 1c4232ca2e6a..6e00073a7331 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2735,9 +2735,16 @@ 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_enabled()) {
+                       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)
-- 
2.12.0