[PATCHv6 5/7] printk: report lost messages in printk safe/nmi contexts

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

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

The patch also moves lost message counter to struct
`printk_safe_seq_buf' instead of having dedicated static
counters - this simplifies the code.

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
---
 kernel/printk/internal.h    | 17 -----------------
 kernel/printk/printk.c      | 10 ----------
 kernel/printk/printk_safe.c | 18 +++++++++++++++---
 3 files changed, 15 insertions(+), 30 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 97cee4f482f4..d2456020120c 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 335b0fcb538e..6ec61ae0d122 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1677,7 +1677,6 @@ 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;
@@ -1728,15 +1727,6 @@ 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 9e8ef6a2070c..cd5160112374 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -42,10 +42,13 @@
 static int printk_safe_irq_ready;
 
 #define SAFE_LOG_BUF_LEN ((1 << CONFIG_PRINTK_SAFE_LOG_BUF_SHIFT) -	\
-			 sizeof(atomic_t) - sizeof(struct irq_work))
+				sizeof(atomic_t) -			\
+				sizeof(atomic_t) -			\
+				sizeof(struct irq_work))
 
 struct printk_safe_seq_buf {
 	atomic_t		len;	/* length of written data */
+	atomic_t		message_lost;
 	struct irq_work		work;	/* IRQ work that flushes the buffer */
 	unsigned char		buffer[SAFE_LOG_BUF_LEN];
 };
@@ -55,7 +58,6 @@ static DEFINE_PER_CPU(int, printk_context);
 
 #ifdef CONFIG_PRINTK_NMI
 static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
-atomic_t nmi_message_lost;
 #endif
 
 /*
@@ -79,7 +81,7 @@ static int printk_safe_log_store(struct printk_safe_seq_buf *s,
 
 	/* The trailing '\0' is not counted into len. */
 	if (len >= sizeof(s->buffer) - 1) {
-		atomic_inc(&nmi_message_lost);
+		atomic_inc(&s->message_lost);
 		return 0;
 	}
 
@@ -168,6 +170,14 @@ static int printk_safe_flush_buffer(const char *start, size_t len)
 	return len;
 }
 
+static void report_message_lost(struct printk_safe_seq_buf *s)
+{
+	int lost = atomic_xchg(&s->message_lost, 0);
+
+	if (lost)
+		printk_deferred("Lost %d message(s)!\n", lost);
+}
+
 /*
  * Flush data from the associated per-CPU buffer. The function
  * can be called either via IRQ work or independently.
@@ -224,6 +234,8 @@ static void __printk_safe_flush(struct irq_work *work)
 	if (atomic_cmpxchg(&s->len, len, 0) != len)
 		goto more;
 
+	report_message_lost(s);
+
 out:
 	raw_spin_unlock_irqrestore(&read_lock, flags);
 }
-- 
2.11.0