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Date: Thu, 1 Dec 2016 22:55:44 +0900
From: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>,
Petr Mladek <pmladek@...e.com>
Cc: Jan Kara <jack@...e.cz>, Tejun Heo <tj@...nel.org>,
Calvin Owens <calvinowens@...com>,
Thomas Gleixner <tglx@...utronix.de>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
Andy Lutomirski <luto@...nel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>,
linux-kernel@...r.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Subject: [RFC][PATCHv5 5/7] printk: report lost messages in printk safe/nmi contexts
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@...il.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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