linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
* [PATCH] tracing: Account bottom half disabled sections.
@ 2021-12-10 20:31 Sebastian Andrzej Siewior
  2021-12-11  1:32 ` Steven Rostedt
  0 siblings, 1 reply; 4+ messages in thread
From: Sebastian Andrzej Siewior @ 2021-12-10 20:31 UTC (permalink / raw)
  To: Steven Rostedt; +Cc: linux-kernel, Ingo Molnar, Peter Zijlstra, Thomas Gleixner

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>
---
 include/linux/trace_events.h | 1 +
 kernel/trace/trace.c         | 6 ++++--
 kernel/trace/trace_output.c  | 3 +++
 3 files changed, 8 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..dca48d556ee5a 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;
@@ -4185,7 +4187,7 @@ static void print_lat_help_header(struct seq_file *m)
 	seq_puts(m, "#                    _------=> CPU#            \n"
 		    "#                   / _-----=> irqs-off        \n"
 		    "#                  | / _----=> need-resched    \n"
-		    "#                  || / _---=> hardirq/softirq \n"
+		    "#                  || / _---=> hardirq/softirq/BH-disables\n"
 		    "#                  ||| / _--=> preempt-depth   \n"
 		    "#                  |||| / _-=> migrate-disable \n"
 		    "#                  ||||| /     delay           \n"
@@ -4226,7 +4228,7 @@ static void print_func_help_header_irq(struct array_buffer *buf, struct seq_file
 
 	seq_printf(m, "#                            %.*s  _-----=> irqs-off\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| / _---=> hardirq/softirq/BH-disabled\n", prec, space);
 	seq_printf(m, "#                            %.*s|| / _--=> preempt-depth\n", prec, space);
 	seq_printf(m, "#                            %.*s||| / _-=> migrate-disable\n", prec, space);
 	seq_printf(m, "#                            %.*s|||| /     delay\n", prec, space);
diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
index 3547e7176ff79..6be644d35ec30 100644
--- a/kernel/trace/trace_output.c
+++ b/kernel/trace/trace_output.c
@@ -445,11 +445,13 @@ 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) ? 'd' :
@@ -478,6 +480,7 @@ int trace_print_lat_fmt(struct trace_seq *s, struct trace_entry *entry)
 		(hardirq && softirq) ? 'H' :
 		hardirq              ? 'h' :
 		softirq              ? 's' :
+		bh_off		     ? 'b' :
 		                       '.' ;
 
 	trace_seq_printf(s, "%c%c%c",
-- 
2.34.1


^ permalink raw reply related	[flat|nested] 4+ messages in thread
* Re: [PATCH] tracing: Account bottom half disabled sections.
  2021-12-10 20:31 [PATCH] tracing: Account bottom half disabled sections Sebastian Andrzej Siewior
@ 2021-12-11  1:32 ` Steven Rostedt
  2021-12-13  9:28   ` Sebastian Andrzej Siewior
  0 siblings, 1 reply; 4+ messages in thread
From: Steven Rostedt @ 2021-12-11  1:32 UTC (permalink / raw)
  To: Sebastian Andrzej Siewior
  Cc: linux-kernel, Ingo Molnar, Peter Zijlstra, Thomas Gleixner

On Fri, 10 Dec 2021 21:31:27 +0100
Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:

> 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>
> ---
>  include/linux/trace_events.h | 1 +
>  kernel/trace/trace.c         | 6 ++++--
>  kernel/trace/trace_output.c  | 3 +++
>  3 files changed, 8 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..dca48d556ee5a 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;
> @@ -4185,7 +4187,7 @@ static void print_lat_help_header(struct seq_file *m)
>  	seq_puts(m, "#                    _------=> CPU#            \n"
>  		    "#                   / _-----=> irqs-off        \n"
>  		    "#                  | / _----=> need-resched    \n"
> -		    "#                  || / _---=> hardirq/softirq \n"
> +		    "#                  || / _---=> hardirq/softirq/BH-disables\n"
>  		    "#                  ||| / _--=> preempt-depth   \n"
>  		    "#                  |||| / _-=> migrate-disable \n"
>  		    "#                  ||||| /     delay           \n"
> @@ -4226,7 +4228,7 @@ static void print_func_help_header_irq(struct array_buffer *buf, struct seq_file
>  
>  	seq_printf(m, "#                            %.*s  _-----=> irqs-off\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| / _---=> hardirq/softirq/BH-disabled\n", prec, space);

So I went to update the documentation on this, and realized that this is
wrong. Really, we want this in the irqs-off section probably.

Note, the above is to show we are running in a hardirq or softirq context.
But BH-disabled does not match that. Should this be with irqs-off being:

 d - irqs are disabled
 b - BH is disabled?
 D - irqs and BH is disabled?

-- Steve


>  	seq_printf(m, "#                            %.*s|| / _--=> preempt-depth\n", prec, space);
>  	seq_printf(m, "#                            %.*s||| / _-=> migrate-disable\n", prec, space);
>  	seq_printf(m, "#                            %.*s|||| /     delay\n", prec, space);
> diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> index 3547e7176ff79..6be644d35ec30 100644

^ permalink raw reply	[flat|nested] 4+ messages in thread
* Re: [PATCH] tracing: Account bottom half disabled sections.
  2021-12-11  1:32 ` Steven Rostedt
@ 2021-12-13  9:28   ` Sebastian Andrzej Siewior
  2021-12-13 10:08     ` [PATCH v2] " Sebastian Andrzej Siewior
  0 siblings, 1 reply; 4+ messages in thread
From: Sebastian Andrzej Siewior @ 2021-12-13  9:28 UTC (permalink / raw)
  To: Steven Rostedt; +Cc: linux-kernel, Ingo Molnar, Peter Zijlstra, Thomas Gleixner

On 2021-12-10 20:32:40 [-0500], Steven Rostedt wrote:
> > @@ -4226,7 +4228,7 @@ static void print_func_help_header_irq(struct array_buffer *buf, struct seq_file
> >  
> >  	seq_printf(m, "#                            %.*s  _-----=> irqs-off\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| / _---=> hardirq/softirq/BH-disabled\n", prec, space);
> 
> So I went to update the documentation on this, and realized that this is
> wrong. Really, we want this in the irqs-off section probably.
> 
> Note, the above is to show we are running in a hardirq or softirq context.
> But BH-disabled does not match that. Should this be with irqs-off being:
> 
>  d - irqs are disabled
>  b - BH is disabled?
>  D - irqs and BH is disabled?

We are not in hardirq/softirq/nmi but have simply BH disabled.
Makes sense.

> -- Steve

Sebastian

^ permalink raw reply	[flat|nested] 4+ messages in thread
* [PATCH v2] tracing: Account bottom half disabled sections.
  2021-12-13  9:28   ` Sebastian Andrzej Siewior
@ 2021-12-13 10:08     ` Sebastian Andrzej Siewior
  0 siblings, 0 replies; 4+ messages in thread
From: Sebastian Andrzej Siewior @ 2021-12-13 10:08 UTC (permalink / raw)
  To: Steven Rostedt; +Cc: linux-kernel, Ingo Molnar, Peter Zijlstra, Thomas Gleixner

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


^ permalink raw reply related	[flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-12-13 10:35 UTC | newest]

Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2021-12-10 20:31 [PATCH] tracing: Account bottom half disabled sections Sebastian Andrzej Siewior
2021-12-11  1:32 ` Steven Rostedt
2021-12-13  9:28   ` Sebastian Andrzej Siewior
2021-12-13 10:08     ` [PATCH v2] " Sebastian Andrzej Siewior

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).