linux-kernel - [RFC][PATCHv6 01/12] printk: move printk

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Date:   Mon,  4 Dec 2017 22:48:14 +0900
From:   Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To:     Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     Jan Kara <jack@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Pavel Machek <pavel@....cz>,
        Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>
Subject: [RFC][PATCHv6 01/12] printk: move printk_pending out of per-cpu

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@...il.com>
Suggested-by: Petr Mladek <pmladek@...e.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