[RFC][PATCHv6 01/12] printk: move printk_pending out of per-cpu

Sergey Senozhatsky
2017-12-04T13:48:53Z

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.senozhatsky@gmail.com>
Suggested-by: Petr Mladek <pmladek@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 8aa27be96012..81c19e51a4a4 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -401,6 +401,14 @@ DEFINE_RAW_SPINLOCK(logbuf_lock);
} while (0)

#ifdef CONFIG_PRINTK
+/*
+ * Delayed printk version, for scheduler-internal messages:
+ */
+#define PRINTK_PENDING_WAKEUP 0x01
+#define PRINTK_PENDING_OUTPUT 0x02
+
+static unsigned long printk_pending;
+
DECLARE_WAIT_QUEUE_HEAD(log_wait);
/* the next printk record to read by syslog(READ) or /proc/kmsg */
static u64 syslog_seq;
@@ -2677,25 +2685,15 @@ 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);
}

@@ -2708,7 +2706,7 @@ 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();
@@ -2721,7 +2719,7 @@ int vprintk_deferred(const char *fmt, va_list args)
r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args);

preempt_disable();
- __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();

--
2.15.1