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tracing: Account bottom half disabled sections.

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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: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
This commit is contained in:
Sebastian Andrzej Siewior 2021-12-13 11:08:53 +01:00 committed by Steven Rostedt
parent 86599dbe2c
commit 289e7b0f7e
3 changed files with 9 additions and 2 deletions
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1
include/linux/trace_events.h
View File

@ -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

6
kernel/trace/trace.c
View File

@ -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);

4
kernel/trace/trace_output.c
View File

@ -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' :
'.';