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Subject[PATCHv7 5/8] printk: report lost messages in printk safe/nmi contexts
Date
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>
---
kernel/printk/internal.h | 17 -----------------
kernel/printk/printk.c | 10 ----------
kernel/printk/printk_safe.c | 38 ++++++++++++++++++++++++++++----------
3 files changed, 28 insertions(+), 37 deletions(-)

diff --git a/kernel/printk/internal.h b/kernel/printk/internal.h
index c65e36509f3b..1db044f808b7 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 9cc9a97c2cc8..86f3f03faf6f 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -1676,7 +1676,6 @@ 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;
@@ -1727,15 +1726,6 @@ 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 054c9128ade0..04fff7074cce 100644
--- a/kernel/printk/printk_safe.c
+++ b/kernel/printk/printk_safe.c
@@ -40,13 +40,15 @@
* were handled or when IRQs are blocked.
*/
static int printk_safe_irq_ready;
-atomic_t nmi_message_lost;

#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];
};
@@ -58,6 +60,16 @@ static DEFINE_PER_CPU(int, printk_context);
static DEFINE_PER_CPU(struct printk_safe_seq_buf, nmi_print_seq);
#endif

+/* Get flushed in a more safe context. */
+static void queue_flush_work(struct printk_safe_seq_buf *s)
+{
+ if (printk_safe_irq_ready) {
+ /* Make sure that IRQ work is really initialized. */
+ smp_rmb();
+ irq_work_queue(&s->work);
+ }
+}
+
/*
* Add a message to per-CPU context-dependent buffer. NMI and printk-safe
* have dedicated buffers, because otherwise printk-safe preempted by
@@ -79,7 +91,8 @@ 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);
+ queue_flush_work(s);
return 0;
}

@@ -91,6 +104,8 @@ static int printk_safe_log_store(struct printk_safe_seq_buf *s,
smp_rmb();

add = vscnprintf(s->buffer + len, sizeof(s->buffer) - len, fmt, args);
+ if (!add)
+ return 0;

/*
* Do it once again if the buffer has been flushed in the meantime.
@@ -100,13 +115,7 @@ static int printk_safe_log_store(struct printk_safe_seq_buf *s,
if (atomic_cmpxchg(&s->len, len, len + add) != len)
goto again;

- /* Get flushed in a more safe context. */
- if (add && printk_safe_irq_ready) {
- /* Make sure that IRQ work is really initialized. */
- smp_rmb();
- irq_work_queue(&s->work);
- }
-
+ queue_flush_work(s);
return add;
}

@@ -168,6 +177,14 @@ 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.
@@ -225,6 +242,7 @@ static void __printk_safe_flush(struct irq_work *work)
goto more;

out:
+ report_message_lost(s);
raw_spin_unlock_irqrestore(&read_lock, flags);
}

--
2.11.0
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