[RFC][PATCHv3 4/6] printk: report lost messages in printk safe/nmi contexts

Sergey Senozhatsky
2016-10-18T15:42:52Z

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.senozhatsky@gmail.com>
---
kernel/printk/internal.h | 17 ---------------
kernel/printk/printk.c | 10 ---------
kernel/printk/printk_safe.c | 50 +++++++++++++++++++++++++++++++++++++++++++--
3 files changed, 48 insertions(+), 29 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index 015f68f..375fe6d 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 58cfc5c..a99414b 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1791,7 +1791,6 @@ 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;
@@ -1842,15 +1841,6 @@ 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 a2b0b99..df66d99 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_safe_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,
@@ -122,6 +123,41 @@ static void printk_safe_flush_seq_line(struct printk_safe_seq_buf *s,
printk_safe_flush_line(buf, (end - start) + 1);
}

+static void report_message_lost(atomic_t *num_lost, char *fmt)
+{
+ int lost = atomic_xchg(num_lost, 0);
+
+ if (lost) {
+ char msg[56];
+
+ scnprintf(msg, sizeof(msg), fmt, lost);
+
+ printk_safe_flush_line(msg, strlen(msg));
+ }
+}
+
+#ifdef CONFIG_PRINTK_NMI
+
+static void report_nmi_message_lost(void)
+{
+ report_message_lost(&nmi_message_lost,
+ "Lost %d message(s) from NMI context!");
+}
+
+#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,
+ "Lost %d message(s) from printk-safe context!");
+}
+
/*
* Flush data from the associated per-CPU buffer. The function
* can be called either via IRQ work or independently.
@@ -147,6 +183,9 @@ static void __printk_safe_flush(struct irq_work *work)

i = 0;
more:
+ report_nmi_message_lost();
+ report_safe_message_lost();
+
len = atomic_read(&s->len);

/*
@@ -289,8 +328,15 @@ 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 == -E2BIG) {
+ atomic_inc(&safe_message_lost);
+ add = 0;
+ }
+
+ return add;
}

/*
--
2.10.1.382.ga23ca1b