Commit 289e7b0f authored by Sebastian Andrzej Siewior's avatar Sebastian Andrzej Siewior Committed by Steven Rostedt
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tracing: Account bottom half disabled sections. 

Disabling only bottom halves via local_bh_disable() disables also
preemption but this remains invisible to tracing. On a CONFIG_PREEMPT
kernel one might wonder why there is no scheduling happening despite the
N flag in the trace. The reason might be the a rcu_read_lock_bh()
section.

Add a 'b' to the tracing output if in task context with disabled bottom
halves.

Link: https://lkml.kernel.org/r/YbcbtdtC/bjCKo57@linutronix.de



Signed-off-by: default avatarSebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: default avatarSteven Rostedt <rostedt@goodmis.org>
parent 86599dbe

include/linux/trace_events.h

+1 −0
Original line number Diff line number Diff line
@@ -172,6 +172,7 @@ enum trace_flag_type { 
	TRACE_FLAG_SOFTIRQ		= 0x10,

	TRACE_FLAG_PREEMPT_RESCHED	= 0x20,

	TRACE_FLAG_NMI			= 0x40,

	TRACE_FLAG_BH_OFF		= 0x80,

};



#ifdef CONFIG_TRACE_IRQFLAGS_SUPPORT

kernel/trace/trace.c

+4 −2
Original line number Diff line number Diff line
@@ -2603,6 +2603,8 @@ unsigned int tracing_gen_ctx_irq_test(unsigned int irqs_status) 
		trace_flags |= TRACE_FLAG_HARDIRQ;

	if (in_serving_softirq())

		trace_flags |= TRACE_FLAG_SOFTIRQ;

	if (softirq_count() >> (SOFTIRQ_SHIFT + 1))

		trace_flags |= TRACE_FLAG_BH_OFF;



	if (tif_need_resched())

		trace_flags |= TRACE_FLAG_NEED_RESCHED;
@@ -4190,7 +4192,7 @@ unsigned long trace_total_entries(struct trace_array *tr) 
static void print_lat_help_header(struct seq_file *m)

{

	seq_puts(m, "#                    _------=> CPU#            \n"

		    "#                   / _-----=> irqs-off        \n"

		    "#                   / _-----=> irqs-off/BH-disabled\n"

		    "#                  | / _----=> need-resched    \n"

		    "#                  || / _---=> hardirq/softirq \n"

		    "#                  ||| / _--=> preempt-depth   \n"
@@ -4231,7 +4233,7 @@ static void print_func_help_header_irq(struct array_buffer *buf, struct seq_file 


	print_event_info(buf, m);



	seq_printf(m, "#                            %.*s  _-----=> irqs-off\n", prec, space);

	seq_printf(m, "#                            %.*s  _-----=> irqs-off/BH-disabled\n", prec, space);

	seq_printf(m, "#                            %.*s / _----=> need-resched\n", prec, space);

	seq_printf(m, "#                            %.*s| / _---=> hardirq/softirq\n", prec, space);

	seq_printf(m, "#                            %.*s|| / _--=> preempt-depth\n", prec, space);

kernel/trace/trace_output.c

+4 −0
Original line number Diff line number Diff line
@@ -445,14 +445,18 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry) 
	char irqs_off;

	int hardirq;

	int softirq;

	int bh_off;

	int nmi;



	nmi = entry->flags & TRACE_FLAG_NMI;

	hardirq = entry->flags & TRACE_FLAG_HARDIRQ;

	softirq = entry->flags & TRACE_FLAG_SOFTIRQ;

	bh_off = entry->flags & TRACE_FLAG_BH_OFF;



	irqs_off =

		(entry->flags & TRACE_FLAG_IRQS_OFF && bh_off) ? 'D' :

		(entry->flags & TRACE_FLAG_IRQS_OFF) ? 'd' :

		bh_off ? 'b' :

		(entry->flags & TRACE_FLAG_IRQS_NOSUPPORT) ? 'X' :

		'.';