printk: report lost messages in printk safe/nmi contexts (ddb9baa8) · Commits · 戴 / test

kernel/printk/internal.h

+0 −17

Original line number	Diff line number	Diff line
		@@ -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

kernel/printk/printk.c

+0 −10

Original line number	Diff line number	Diff line
		@@ -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.

kernel/printk/printk_safe.c

+28 −10

Original line number	Diff line number	Diff line
		@@ -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 @@ again:

		/* 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 @@ again:
		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 @@ again:
		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 @@ more:
		goto more;

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

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