+ printk-nmi-use-irq-work-only-when-ready.patch added to -mm tree

[akpm@linux-foundation.org]

The patch titled
     Subject: printk/nmi: use IRQ work only when ready
has been added to the -mm tree.  Its filename is
     printk-nmi-use-irq-work-only-when-ready.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/printk-nmi-use-irq-work-only-when-ready.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/printk-nmi-use-irq-work-only-when-ready.patch

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------------------------------------------------------
From: Petr Mladek <pmladek@suse.com>
Subject: printk/nmi: use IRQ work only when ready

NMIs could happen at any time.  This patch makes sure that the safe
printk() in NMI will schedule IRQ work only when the related structs are
initialized.

All pending messages are flushed when the IRQ work is being initialized.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jiri Kosina <jkosina@suse.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 kernel/printk/nmi.c |   13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff -puN kernel/printk/nmi.c~printk-nmi-use-irq-work-only-when-ready kernel/printk/nmi.c
--- a/kernel/printk/nmi.c~printk-nmi-use-irq-work-only-when-ready
+++ a/kernel/printk/nmi.c
@@ -38,6 +38,7 @@
  * were handled or when IRQs are blocked.
  */
 DEFINE_PER_CPU(printk_func_t, printk_func) = vprintk_default;
+static int printk_nmi_irq_ready;
 
 #define NMI_LOG_BUF_LEN (4096 - sizeof(atomic_t) - sizeof(struct irq_work))
 
@@ -83,8 +84,11 @@ again:
 		goto again;
 
 	/* Get flushed in a more safe context. */
-	if (add)
+	if (add && printk_nmi_irq_ready) {
+		/* Make sure that IRQ work is really initialized. */
+		smp_rmb();
 		irq_work_queue(&s->work);
+	}
 
 	return add;
 }
@@ -190,6 +194,13 @@ void __init printk_nmi_init(void)
 
 		init_irq_work(&s->work, __printk_nmi_flush);
 	}
+
+	/* Make sure that IRQ works are initialized before enabling. */
+	smp_wmb();
+	printk_nmi_irq_ready = 1;
+
+	/* Flush pending messages that did not have scheduled IRQ works. */
+	printk_nmi_flush();
 }
 
 void printk_nmi_enter(void)
_

Patches currently in -mm which might be from pmladek@suse.com are

printk-nmi-generic-solution-for-safe-printk-in-nmi.patch
printk-nmi-use-irq-work-only-when-ready.patch
printk-nmi-warn-when-some-message-has-been-lost-in-nmi-context.patch
printk-nmi-increase-the-size-of-nmi-buffer-and-make-it-configurable.patch