From ddb9baa822265b55afffd9815a2758a4b70006c1 Mon Sep 17 00:00:00 2001 From: Sergey Senozhatsky Date: Tue, 27 Dec 2016 23:16:08 +0900 Subject: 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(). The patch also moves lost message counter to struct `printk_safe_seq_buf' instead of having dedicated static counters - this simplifies the code. Link: http://lkml.kernel.org/r/20161227141611.940-6-sergey.senozhatsky@gmail.com Cc: Andrew Morton Cc: Linus Torvalds Cc: Steven Rostedt Cc: Jan Kara Cc: Tejun Heo Cc: Calvin Owens Cc: Ingo Molnar Cc: Peter Zijlstra Cc: Andy Lutomirski Cc: Peter Hurley Cc: linux-kernel@vger.kernel.org Signed-off-by: Sergey Senozhatsky Signed-off-by: Petr Mladek --- kernel/printk/printk_safe.c | 38 ++++++++++++++++++++++++++++---------- 1 file changed, 28 insertions(+), 10 deletions(-) (limited to 'kernel/printk/printk_safe.c') diff --git a/kernel/printk/printk_safe.c b/kernel/printk/printk_safe.c index 5214d326d3ba..033e50a7d706 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 @@ 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); } -- cgit