6 files changed, 49 insertions, 3 deletions

diff --git a/include/linux/printk.h b/include/linux/printk.h
index 51dd6b824fe2..f4da695fd615 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -127,11 +127,13 @@ extern void printk_nmi_init(void);
 extern void printk_nmi_enter(void);
 extern void printk_nmi_exit(void);
 extern void printk_nmi_flush(void);
+extern void printk_nmi_flush_on_panic(void);
 #else
 static inline void printk_nmi_init(void) { }
 static inline void printk_nmi_enter(void) { }
 static inline void printk_nmi_exit(void) { }
 static inline void printk_nmi_flush(void) { }
+static inline void printk_nmi_flush_on_panic(void) { }
 #endif /* PRINTK_NMI */
 
 #ifdef CONFIG_PRINTK
diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
index 1c03dfb4abfd..d5d408252992 100644
--- a/kernel/kexec_core.c
+++ b/kernel/kexec_core.c
@@ -893,6 +893,7 @@ void crash_kexec(struct pt_regs *regs)
         old_cpu = atomic_cmpxchg(&panic_cpu, PANIC_CPU_INVALID, this_cpu);
         if (old_cpu == PANIC_CPU_INVALID) {
                 /* This is the 1st CPU which comes here, so go ahead. */
+                printk_nmi_flush_on_panic();
                 __crash_kexec(regs);
 
                 /*
diff --git a/kernel/panic.c b/kernel/panic.c
index 535c96510a44..8aa74497cc5a 100644
--- a/kernel/panic.c
+++ b/kernel/panic.c
@@ -160,8 +160,10 @@ void panic(const char *fmt, ...)
          *
          * Bypass the panic_cpu check and call __crash_kexec directly.
          */
-        if (!crash_kexec_post_notifiers)
+        if (!crash_kexec_post_notifiers) {
+                printk_nmi_flush_on_panic();
                 __crash_kexec(NULL);
+        }
 
         /*
          * Note smp_send_stop is the usual smp shutdown function, which
@@ -176,6 +178,8 @@ void panic(const char *fmt, ...)
          */
         atomic_notifier_call_chain(&panic_notifier_list, 0, buf);
 
+        /* Call flush even twice. It tries harder with a single online CPU */
+        printk_nmi_flush_on_panic();
         kmsg_dump(KMSG_DUMP_PANIC);
 
         /*
diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 341bedccc065..7fd2838fa417 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -22,6 +22,8 @@ int __printf(1, 0) vprintk_default(const char *fmt, va_list args);
 
 #ifdef CONFIG_PRINTK_NMI
 
+extern raw_spinlock_t logbuf_lock;
+
 /*
  * printk() could not take logbuf_lock in NMI context. Instead,
  * it temporary stores the strings into a per-CPU buffer.
diff --git a/kernel/printk/nmi.c b/kernel/printk/nmi.c
index bf08557d7e3d..b69eb8a2876f 100644
--- a/kernel/printk/nmi.c
+++ b/kernel/printk/nmi.c
@@ -17,6 +17,7 @@
 
 #include <linux/preempt.h>
 #include <linux/spinlock.h>
+#include <linux/debug_locks.h>
 #include <linux/smp.h>
 #include <linux/cpumask.h>
 #include <linux/irq_work.h>
@@ -106,7 +107,16 @@ static void print_nmi_seq_line(struct nmi_seq_buf *s, int start, int end)
 {
         const char *buf = s->buffer + start;
 
-        printk("%.*s", (end - start) + 1, buf);
+        /*
+         * The buffers are flushed in NMI only on panic.  The messages must
+         * go only into the ring buffer at this stage.  Consoles will get
+         * explicitly called later when a crashdump is not generated.
+         */
+        if (in_nmi())
+                printk_deferred("%.*s", (end - start) + 1, buf);
+        else
+                printk("%.*s", (end - start) + 1, buf);
+
 }
 
 /*
@@ -194,6 +204,33 @@ void printk_nmi_flush(void)
                 __printk_nmi_flush(&per_cpu(nmi_print_seq, cpu).work);
 }
 
+/**
+ * printk_nmi_flush_on_panic - flush all per-cpu nmi buffers when the system
+ *      goes down.
+ *
+ * Similar to printk_nmi_flush() but it can be called even in NMI context when
+ * the system goes down. It does the best effort to get NMI messages into
+ * the main ring buffer.
+ *
+ * Note that it could try harder when there is only one CPU online.
+ */
+void printk_nmi_flush_on_panic(void)
+{
+        /*
+         * Make sure that we could access the main ring buffer.
+         * Do not risk a double release when more CPUs are up.
+         */
+        if (in_nmi() && raw_spin_is_locked(&logbuf_lock)) {
+                if (num_online_cpus() > 1)
+                        return;
+
+                debug_locks_off();
+                raw_spin_lock_init(&logbuf_lock);
+        }
+
+        printk_nmi_flush();
+}
+
 void __init printk_nmi_init(void)
 {
         int cpu;
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index e38579d730f4..60cdf6386763 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -245,7 +245,7 @@ __packed __aligned(4)
  * within the scheduler's rq lock. It must be released before calling
  * console_unlock() or anything else that might wake up a process.
  */
-static DEFINE_RAW_SPINLOCK(logbuf_lock);
+DEFINE_RAW_SPINLOCK(logbuf_lock);
 
 #ifdef CONFIG_PRINTK
 DECLARE_WAIT_QUEUE_HEAD(log_wait);