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

[Petr Mladek]

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@xxxxxxx>
---
 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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