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Subject[RFC][PATCHv2 3/8] printk: offload printing from wake_up_klogd_work_func()
Date
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.senozhatsky@gmail.com>
---
kernel/printk/printk.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index ab6b3b2a68c6..1927b5cb5cbe 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2741,8 +2741,16 @@ static void wake_up_klogd_work_func(struct irq_work *irq_work)
* If trylock fails, someone else is doing the printing.
* PRINTK_PENDING_OUTPUT bit is cleared by console_unlock().
*/
- 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 (test_and_clear_bit(PRINTK_PENDING_WAKEUP, &printk_pending))
--
2.12.2
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