[RFC][PATCHv3 1/5] printk: move printk_pending out of per-cpu

[Sergey Senozhatsky]

Do not keep `printk_pending' in per-CPU area. We set the following bits
of printk_pending:
a) PRINTK_PENDING_WAKEUP
        when we need to wakeup klogd
b) PRINTK_PENDING_OUTPUT
        when there is a pending output from deferred printk and we need
        to call console_unlock().

So none of the bits control/represent a state of a particular CPU and,
basically, they should be global instead.

Besides we will use `printk_pending' to control printk kthread, so this
patch is also a preparation work.

Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
Suggested-by: Petr Mladek <pmla...@suse.com>
---
 kernel/printk/printk.c | 26 ++++++++++++--------------
 1 file changed, 12 insertions(+), 14 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index a1aecf44ab07..2cb7f4753b76 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -401,6 +401,14 @@ DEFINE_RAW_SPINLOCK(logbuf_lock);
                printk_safe_exit_irqrestore(flags);     \
        } while (0)
 
+/*
+ * Delayed printk version, for scheduler-internal messages:
+ */
+#define PRINTK_PENDING_WAKEUP  0x01
+#define PRINTK_PENDING_OUTPUT  0x02
+
+static unsigned long printk_pending;
+
 #ifdef CONFIG_PRINTK
 DECLARE_WAIT_QUEUE_HEAD(log_wait);
 /* the next printk record to read by syslog(READ) or /proc/kmsg */
@@ -2709,25 +2717,15 @@ static int __init printk_late_init(void)
 late_initcall(printk_late_init);
 
 #if defined CONFIG_PRINTK
-/*
- * Delayed printk version, for scheduler-internal messages:
- */
-#define PRINTK_PENDING_WAKEUP  0x01
-#define PRINTK_PENDING_OUTPUT  0x02
-
-static DEFINE_PER_CPU(int, printk_pending);
-
 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 (test_and_clear_bit(PRINTK_PENDING_OUTPUT, &printk_pending)) {
                /* If trylock fails, someone else is doing the printing */
                if (console_trylock())
                        console_unlock();
        }
 
-       if (pending & PRINTK_PENDING_WAKEUP)
+       if (test_and_clear_bit(PRINTK_PENDING_WAKEUP, &printk_pending))
                wake_up_interruptible(&log_wait);
 }
 
@@ -2740,7 +2738,7 @@ void wake_up_klogd(void)
 {
        preempt_disable();
        if (waitqueue_active(&log_wait)) {
-               this_cpu_or(printk_pending, PRINTK_PENDING_WAKEUP);
+               set_bit(PRINTK_PENDING_WAKEUP, &printk_pending);
                irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
        }
        preempt_enable();
@@ -2756,7 +2754,7 @@ int printk_deferred(const char *fmt, ...)
        r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args);
        va_end(args);
 
-       __this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
+       set_bit(PRINTK_PENDING_OUTPUT, &printk_pending);
        irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
        preempt_enable();
 
-- 
2.12.2