Messages in this thread Patch in this message | | | Date | Mon, 13 Dec 2021 11:08:53 +0100 | From | Sebastian Andrzej Siewior <> | Subject | [PATCH v2] 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.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- v1…v2: - Move output to the IRQ-off section.
include/linux/trace_events.h | 1 + kernel/trace/trace.c | 6 ++++-- kernel/trace/trace_output.c | 4 ++++ 3 files changed, 9 insertions(+), 2 deletions(-)
diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h index 2d167ac3452c5..a2af7e1156eac 100644 --- a/include/linux/trace_events.h +++ b/include/linux/trace_events.h @@ -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 diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 88de94da596b1..c3618dd7ecb4b 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -2601,6 +2601,8 @@ 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; @@ -4183,7 +4185,7 @@ 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" @@ -4224,7 +4226,7 @@ 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); diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c index 3547e7176ff79..8aa493d25c73e 100644 --- a/kernel/trace/trace_output.c +++ b/kernel/trace/trace_output.c @@ -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' : '.'; -- 2.34.1
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