[RFC][PATCH v6 2/2] printk: Make wake_up_klogd_work_func() async

From: Sergey Senozhatsky
Date: Mon Mar 21 2016 - 13:28:16 EST


From: Jan Kara <jack@xxxxxxx>

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@xxxxxxx>
Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@xxxxxxxxx>
---
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 99c105d6..70cde26 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -349,9 +349,16 @@ 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_sync && 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.rc3.12.g047057b