linux-kernel - [PATCH 04/10] printk: Merge and flush NMI buffer predictably via IRQ work

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Date:	Mon, 25 May 2015 14:46:27 +0200
From:	Petr Mladek <pmladek@...e.cz>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Frederic Weisbecker <fweisbec@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dave Anderson <anderson@...hat.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Kay Sievers <kay@...y.org>, Jiri Kosina <jkosina@...e.cz>,
	Michal Hocko <mhocko@...e.cz>, Jan Kara <jack@...e.cz>,
	linux-kernel@...r.kernel.org, Wang Long <long.wanglong@...wei.com>,
	peifeiyue@...wei.com, dzickus@...hat.com, morgan.wang@...wei.com,
	sasha.levin@...cle.com, Petr Mladek <pmladek@...e.cz>
Subject: [PATCH 04/10] printk: Merge and flush NMI buffer predictably via IRQ work

It might take ages until users see messages from NMI context. They cannot
be flushed to the console because the operation involves taking and
releasing a bunch of locks. Everything gets fixed by the followup printk
in normal context but it is not predictable.

The same problem has printk_sched() and this patch reuses the existing
solution.

There is no special printk() variant for NMI context. Hence the IRQ work
need to get queued from vprintk_emit().

Signed-off-by: Petr Mladek <pmladek@...e.cz>
---
 kernel/printk/printk.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index bf2abdda5869..c2ae9ff388ae 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1554,9 +1554,6 @@ int printk_deferred(const char *fmt, ...)
 	va_start(args, fmt);
 	r = vprintk_emit(0, LOGLEVEL_SCHED, NULL, 0, fmt, args);
 	va_end(args);
-
-	__this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
-	irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
 	preempt_enable();
 
 	return r;
@@ -1880,7 +1877,10 @@ asmlinkage int vprintk_emit(int facility, int level,
 	 * If called from the scheduler or NMI context, we can not get console
 	 * without a possible deadlock.
 	 */
-	if (!in_sched && !in_nmi()) {
+	if (in_sched || in_nmi()) {
+		__this_cpu_or(printk_pending, PRINTK_PENDING_OUTPUT);
+		irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));
+	} else {
 		lockdep_off();
 		/*
 		 * Disable preemption to avoid being preempted while holding
-- 
1.8.5.6

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