Account lost messages in pritk-safe and printk-safe-nmi
contexts and report those numbers during printk_safe_flush().

Signed-off-by: Sergey Senozhatsky <sergey.senozhat...@gmail.com>
---
 kernel/printk/internal.h    | 17 -----------------
 kernel/printk/printk.c      | 10 ----------
 kernel/printk/printk_safe.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
 3 files changed, 43 insertions(+), 29 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 97cee4f..d245602 100644
--- a/kernel/printk/internal.h
+++ b/kernel/printk/internal.h
@@ -16,23 +16,6 @@
  */
 #include <linux/percpu.h>
 
-#ifdef CONFIG_PRINTK_NMI
-
-extern atomic_t nmi_message_lost;
-static inline int get_nmi_message_lost(void)
-{
-       return atomic_xchg(&nmi_message_lost, 0);
-}
-
-#else /* CONFIG_PRINTK_NMI */
-
-static inline int get_nmi_message_lost(void)
-{
-       return 0;
-}
-
-#endif /* CONFIG_PRINTK_NMI */
-
 #ifdef CONFIG_PRINTK
 
 #define PRINTK_SAFE_CONTEXT_MASK       0x7fffffff
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index 77446ba..6f7b217 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1776,7 +1776,6 @@ asmlinkage int vprintk_emit(int facility, int level,
        unsigned long flags;
        int this_cpu;
        int printed_len = 0;
-       int nmi_message_lost;
        bool in_sched = false;
        /* cpu currently holding logbuf_lock in this function */
        static unsigned int logbuf_cpu = UINT_MAX;
@@ -1827,15 +1826,6 @@ asmlinkage int vprintk_emit(int facility, int level,
                                         strlen(recursion_msg));
        }
 
-       nmi_message_lost = get_nmi_message_lost();
-       if (unlikely(nmi_message_lost)) {
-               text_len = scnprintf(textbuf, sizeof(textbuf),
-                                    "BAD LUCK: lost %d message(s) from NMI 
context!",
-                                    nmi_message_lost);
-               printed_len += log_store(0, 2, LOG_PREFIX|LOG_NEWLINE, 0,
-                                        NULL, 0, textbuf, text_len);
-       }
-
        /*
         * The printf needs to come first; we need the syslog
         * prefix which might be passed-in as a parameter.
diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c
index 3ded9e1..0689b94 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -52,10 +52,11 @@ struct printk_safe_seq_buf {
 
 static DEFINE_PER_CPU(struct printk_safe_seq_buf, safe_print_seq);
 static DEFINE_PER_CPU(int, printk_context);
+static atomic_t safe_message_lost;
 
 #ifdef CONFIG_PRINTK_NMI
 static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
-atomic_t nmi_message_lost;
+static atomic_t nmi_message_lost;
 #endif
 
 static int printk_safe_log_store(struct printk_safe_seq_buf *s,
@@ -155,6 +156,36 @@ static int printk_safe_flush_buffer(const char *start, 
size_t len)
        return len;
 }
 
+static void report_message_lost(atomic_t *num_lost, const char *context)
+{
+       int lost = atomic_xchg(num_lost, 0);
+
+       if (lost)
+               printk_deferred("Lost %d message(s) from %s context!\n",
+                               lost,
+                               context);
+}
+
+#ifdef CONFIG_PRINTK_NMI
+
+static void report_nmi_message_lost(void)
+{
+       report_message_lost(&nmi_message_lost, "NMI");
+}
+
+#else
+
+static void report_nmi_message_lost(void)
+{
+}
+
+#endif /* CONFIG_PRINTK_NMI */
+
+static void report_safe_message_lost(void)
+{
+       report_message_lost(&safe_message_lost, "printk-safe");
+}
+
 /*
  * Flush data from the associated per-CPU buffer. The function
  * can be called either via IRQ work or independently.
@@ -211,6 +242,9 @@ static void __printk_safe_flush(struct irq_work *work)
        if (atomic_cmpxchg(&s->len, len, 0) != len)
                goto more;
 
+       report_nmi_message_lost();
+       report_safe_message_lost();
+
 out:
        raw_spin_unlock_irqrestore(&read_lock, flags);
 }
@@ -309,8 +343,15 @@ static int vprintk_safe_nmi(const char *fmt, va_list args)
 static int vprintk_safe(const char *fmt, va_list args)
 {
        struct printk_safe_seq_buf *s = this_cpu_ptr(&safe_print_seq);
+       int add;
 
-       return printk_safe_log_store(s, fmt, args);
+       add = printk_safe_log_store(s, fmt, args);
+       if (add == -ENOSPC) {
+               atomic_inc(&safe_message_lost);
+               add = 0;
+       }
+
+       return add;
 }
 
 /* Can be preempted by NMI. */
-- 
2.10.2

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