[RFC][PATCH v8 2/2] printk: Make wake_up_klogd_work_func() async

Sergey Senozhatsky
2016-03-24T15:46:00Z

From: Jan Kara <jack@suse.cz>

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>
---
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 a984c5a..475bfd0 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2812,9 +2812,16 @@ 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.rc3.12.g047057b