[PATCH 1/2 v3] tracing/core: Add current context on tracing recursion warning

[Frederic Weisbecker <fweisbec@gmail.com>]

In case of tracing recursion detection, we only get the stacktrace.
But the current context may be very useful to debug the issue.

This patch adds the softirq/hardirq/nmi context with the warning
using lockdep context display to have a familiar output.

v2: Use printk_once()
v3: drop {hardirq,softirq}_context which depend on lockdep,
    only keep what is part of current->trace_recursion,
    sufficient to debug the warning source.

[ Impact: print context necessary to debug recursion ]

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
---
 kernel/trace/ring_buffer.c |    7 +++++++
 1 files changed, 7 insertions(+), 0 deletions(-)

diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
index b421b0e..bffde63 100644
--- a/kernel/trace/ring_buffer.c
+++ b/kernel/trace/ring_buffer.c
@@ -1495,6 +1495,13 @@ static int trace_recursive_lock(void)
 	if (unlikely(current->trace_recursion & (1 << level))) {
 		/* Disable all tracing before we do anything else */
 		tracing_off_permanent();
+
+		printk_once(KERN_WARNING "Tracing recursion: "
+			    "HC[%lu]:SC[%lu]:NMI[%lu]\n",
+			    hardirq_count() >> HARDIRQ_SHIFT,
+			    softirq_count() >> SOFTIRQ_SHIFT,
+			    in_nmi());
+
 		WARN_ON_ONCE(1);
 		return -1;
 	}
-- 
1.6.2.3