[RESEND,v2] tracing: Rename stacktrace field to common_stacktrace

  From: "Steven Rostedt (Google)" <rostedt@goodmis.org>

The histogram and synthetic events can use a pseudo event called
"stacktrace" that will create a stacktrace at the time of the event and
use it just like it was a normal field. We have other pseudo events such
as "common_cpu" and "common_timestamp". To stay consistent with that,
convert "stacktrace" to "common_stacktrace". As this was used in older
kernels, to keep backward compatibility, this will act just like
"common_cpu" did with "cpu". That is, "cpu" will be the same as
"common_cpu" unless the event has a "cpu" field. In which case, the
event's field is used. The same is true with "stacktrace".

Also update the documentation to reflect this change.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
Resending to get rid of the junk I left at the top the first time.

Changes since v1: https://lore.kernel.org/linux-trace-kernel/20230523221108.064a5d82@rorschach.local.home/
 - Update the tracefs README to use common_stacktrace instead of
   just stacktrace

 Documentation/trace/histogram.rst | 64 +++++++++++++++----------------
 include/linux/trace_events.h      |  1 +
 kernel/trace/trace.c              |  2 +-
 kernel/trace/trace_events.c       |  2 +
 kernel/trace/trace_events_hist.c  | 16 +++++---
 5 files changed, 46 insertions(+), 39 deletions(-)
  

On Tue, 23 May 2023 23:09:13 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: "Steven Rostedt (Google)" <rostedt@goodmis.org>
> 
> The histogram and synthetic events can use a pseudo event called
> "stacktrace" that will create a stacktrace at the time of the event and
> use it just like it was a normal field. We have other pseudo events such
> as "common_cpu" and "common_timestamp". To stay consistent with that,
> convert "stacktrace" to "common_stacktrace". As this was used in older
> kernels, to keep backward compatibility, this will act just like
> "common_cpu" did with "cpu". That is, "cpu" will be the same as
> "common_cpu" unless the event has a "cpu" field. In which case, the
> event's field is used. The same is true with "stacktrace".
> 
> Also update the documentation to reflect this change.
> 

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>

Thanks,

> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
> Resending to get rid of the junk I left at the top the first time.
> 
> Changes since v1: https://lore.kernel.org/linux-trace-kernel/20230523221108.064a5d82@rorschach.local.home/
>  - Update the tracefs README to use common_stacktrace instead of
>    just stacktrace
> 
>  Documentation/trace/histogram.rst | 64 +++++++++++++++----------------
>  include/linux/trace_events.h      |  1 +
>  kernel/trace/trace.c              |  2 +-
>  kernel/trace/trace_events.c       |  2 +
>  kernel/trace/trace_events_hist.c  | 16 +++++---
>  5 files changed, 46 insertions(+), 39 deletions(-)
> 
> diff --git a/Documentation/trace/histogram.rst b/Documentation/trace/histogram.rst
> index 479c9eac6335..3c9b263de9c2 100644
> --- a/Documentation/trace/histogram.rst
> +++ b/Documentation/trace/histogram.rst
> @@ -35,7 +35,7 @@ Documentation written by Tom Zanussi
>    in place of an explicit value field - this is simply a count of
>    event hits.  If 'values' isn't specified, an implicit 'hitcount'
>    value will be automatically created and used as the only value.
> -  Keys can be any field, or the special string 'stacktrace', which
> +  Keys can be any field, or the special string 'common_stacktrace', which
>    will use the event's kernel stacktrace as the key.  The keywords
>    'keys' or 'key' can be used to specify keys, and the keywords
>    'values', 'vals', or 'val' can be used to specify values.  Compound
> @@ -54,7 +54,7 @@ Documentation written by Tom Zanussi
>    'compatible' if the fields named in the trigger share the same
>    number and type of fields and those fields also have the same names.
>    Note that any two events always share the compatible 'hitcount' and
> -  'stacktrace' fields and can therefore be combined using those
> +  'common_stacktrace' fields and can therefore be combined using those
>    fields, however pointless that may be.
>  
>    'hist' triggers add a 'hist' file to each event's subdirectory.
> @@ -547,9 +547,9 @@ Extended error information
>    the hist trigger display symbolic call_sites, we can have the hist
>    trigger additionally display the complete set of kernel stack traces
>    that led to each call_site.  To do that, we simply use the special
> -  value 'stacktrace' for the key parameter::
> +  value 'common_stacktrace' for the key parameter::
>  
> -    # echo 'hist:keys=stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
> +    # echo 'hist:keys=common_stacktrace:values=bytes_req,bytes_alloc:sort=bytes_alloc' > \
>             /sys/kernel/tracing/events/kmem/kmalloc/trigger
>  
>    The above trigger will use the kernel stack trace in effect when an
> @@ -561,9 +561,9 @@ Extended error information
>    every callpath to a kmalloc for a kernel compile)::
>  
>      # cat /sys/kernel/tracing/events/kmem/kmalloc/hist
> -    # trigger info: hist:keys=stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
> +    # trigger info: hist:keys=common_stacktrace:vals=bytes_req,bytes_alloc:sort=bytes_alloc:size=2048 [active]
>  
> -    { stacktrace:
> +    { common_stacktrace:
>           __kmalloc_track_caller+0x10b/0x1a0
>           kmemdup+0x20/0x50
>           hidraw_report_event+0x8a/0x120 [hid]
> @@ -581,7 +581,7 @@ Extended error information
>           cpu_startup_entry+0x315/0x3e0
>           rest_init+0x7c/0x80
>      } hitcount:          3  bytes_req:         21  bytes_alloc:         24
> -    { stacktrace:
> +    { common_stacktrace:
>           __kmalloc_track_caller+0x10b/0x1a0
>           kmemdup+0x20/0x50
>           hidraw_report_event+0x8a/0x120 [hid]
> @@ -596,7 +596,7 @@ Extended error information
>           do_IRQ+0x5a/0xf0
>           ret_from_intr+0x0/0x30
>      } hitcount:          3  bytes_req:         21  bytes_alloc:         24
> -    { stacktrace:
> +    { common_stacktrace:
>           kmem_cache_alloc_trace+0xeb/0x150
>           aa_alloc_task_context+0x27/0x40
>           apparmor_cred_prepare+0x1f/0x50
> @@ -608,7 +608,7 @@ Extended error information
>      .
>      .
>      .
> -    { stacktrace:
> +    { common_stacktrace:
>           __kmalloc+0x11b/0x1b0
>           i915_gem_execbuffer2+0x6c/0x2c0 [i915]
>           drm_ioctl+0x349/0x670 [drm]
> @@ -616,7 +616,7 @@ Extended error information
>           SyS_ioctl+0x81/0xa0
>           system_call_fastpath+0x12/0x6a
>      } hitcount:      17726  bytes_req:   13944120  bytes_alloc:   19593808
> -    { stacktrace:
> +    { common_stacktrace:
>           __kmalloc+0x11b/0x1b0
>           load_elf_phdrs+0x76/0xa0
>           load_elf_binary+0x102/0x1650
> @@ -625,7 +625,7 @@ Extended error information
>           SyS_execve+0x3a/0x50
>           return_from_execve+0x0/0x23
>      } hitcount:      33348  bytes_req:   17152128  bytes_alloc:   20226048
> -    { stacktrace:
> +    { common_stacktrace:
>           kmem_cache_alloc_trace+0xeb/0x150
>           apparmor_file_alloc_security+0x27/0x40
>           security_file_alloc+0x16/0x20
> @@ -636,7 +636,7 @@ Extended error information
>           SyS_open+0x1e/0x20
>           system_call_fastpath+0x12/0x6a
>      } hitcount:    4766422  bytes_req:    9532844  bytes_alloc:   38131376
> -    { stacktrace:
> +    { common_stacktrace:
>           __kmalloc+0x11b/0x1b0
>           seq_buf_alloc+0x1b/0x50
>           seq_read+0x2cc/0x370
> @@ -1026,7 +1026,7 @@ Extended error information
>    First we set up an initially paused stacktrace trigger on the
>    netif_receive_skb event::
>  
> -    # echo 'hist:key=stacktrace:vals=len:pause' > \
> +    # echo 'hist:key=common_stacktrace:vals=len:pause' > \
>             /sys/kernel/tracing/events/net/netif_receive_skb/trigger
>  
>    Next, we set up an 'enable_hist' trigger on the sched_process_exec
> @@ -1060,9 +1060,9 @@ Extended error information
>      $ wget https://www.kernel.org/pub/linux/kernel/v3.x/patch-3.19.xz
>  
>      # cat /sys/kernel/tracing/events/net/netif_receive_skb/hist
> -    # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
> +    # trigger info: hist:keys=common_stacktrace:vals=len:sort=hitcount:size=2048 [paused]
>  
> -    { stacktrace:
> +    { common_stacktrace:
>           __netif_receive_skb_core+0x46d/0x990
>           __netif_receive_skb+0x18/0x60
>           netif_receive_skb_internal+0x23/0x90
> @@ -1079,7 +1079,7 @@ Extended error information
>           kthread+0xd2/0xf0
>           ret_from_fork+0x42/0x70
>      } hitcount:         85  len:      28884
> -    { stacktrace:
> +    { common_stacktrace:
>           __netif_receive_skb_core+0x46d/0x990
>           __netif_receive_skb+0x18/0x60
>           netif_receive_skb_internal+0x23/0x90
> @@ -1097,7 +1097,7 @@ Extended error information
>           irq_thread+0x11f/0x150
>           kthread+0xd2/0xf0
>      } hitcount:         98  len:     664329
> -    { stacktrace:
> +    { common_stacktrace:
>           __netif_receive_skb_core+0x46d/0x990
>           __netif_receive_skb+0x18/0x60
>           process_backlog+0xa8/0x150
> @@ -1115,7 +1115,7 @@ Extended error information
>           inet_sendmsg+0x64/0xa0
>           sock_sendmsg+0x3d/0x50
>      } hitcount:        115  len:      13030
> -    { stacktrace:
> +    { common_stacktrace:
>           __netif_receive_skb_core+0x46d/0x990
>           __netif_receive_skb+0x18/0x60
>           netif_receive_skb_internal+0x23/0x90
> @@ -1142,14 +1142,14 @@ Extended error information
>    into the histogram.  In order to avoid having to set everything up
>    again, we can just clear the histogram first::
>  
> -    # echo 'hist:key=stacktrace:vals=len:clear' >> \
> +    # echo 'hist:key=common_stacktrace:vals=len:clear' >> \
>             /sys/kernel/tracing/events/net/netif_receive_skb/trigger
>  
>    Just to verify that it is in fact cleared, here's what we now see in
>    the hist file::
>  
>      # cat /sys/kernel/tracing/events/net/netif_receive_skb/hist
> -    # trigger info: hist:keys=stacktrace:vals=len:sort=hitcount:size=2048 [paused]
> +    # trigger info: hist:keys=common_stacktrace:vals=len:sort=hitcount:size=2048 [paused]
>  
>      Totals:
>          Hits: 0
> @@ -1485,12 +1485,12 @@ Extended error information
>  
>    And here's an example that shows how to combine histogram data from
>    any two events even if they don't share any 'compatible' fields
> -  other than 'hitcount' and 'stacktrace'.  These commands create a
> +  other than 'hitcount' and 'common_stacktrace'.  These commands create a
>    couple of triggers named 'bar' using those fields::
>  
> -    # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
> +    # echo 'hist:name=bar:key=common_stacktrace:val=hitcount' > \
>             /sys/kernel/tracing/events/sched/sched_process_fork/trigger
> -    # echo 'hist:name=bar:key=stacktrace:val=hitcount' > \
> +    # echo 'hist:name=bar:key=common_stacktrace:val=hitcount' > \
>            /sys/kernel/tracing/events/net/netif_rx/trigger
>  
>    And displaying the output of either shows some interesting if
> @@ -1501,16 +1501,16 @@ Extended error information
>  
>      # event histogram
>      #
> -    # trigger info: hist:name=bar:keys=stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
> +    # trigger info: hist:name=bar:keys=common_stacktrace:vals=hitcount:sort=hitcount:size=2048 [active]
>      #
>  
> -    { stacktrace:
> +    { common_stacktrace:
>               kernel_clone+0x18e/0x330
>               kernel_thread+0x29/0x30
>               kthreadd+0x154/0x1b0
>               ret_from_fork+0x3f/0x70
>      } hitcount:          1
> -    { stacktrace:
> +    { common_stacktrace:
>               netif_rx_internal+0xb2/0xd0
>               netif_rx_ni+0x20/0x70
>               dev_loopback_xmit+0xaa/0xd0
> @@ -1528,7 +1528,7 @@ Extended error information
>               call_cpuidle+0x3b/0x60
>               cpu_startup_entry+0x22d/0x310
>      } hitcount:          1
> -    { stacktrace:
> +    { common_stacktrace:
>               netif_rx_internal+0xb2/0xd0
>               netif_rx_ni+0x20/0x70
>               dev_loopback_xmit+0xaa/0xd0
> @@ -1543,7 +1543,7 @@ Extended error information
>               SyS_sendto+0xe/0x10
>               entry_SYSCALL_64_fastpath+0x12/0x6a
>      } hitcount:          2
> -    { stacktrace:
> +    { common_stacktrace:
>               netif_rx_internal+0xb2/0xd0
>               netif_rx+0x1c/0x60
>               loopback_xmit+0x6c/0xb0
> @@ -1561,7 +1561,7 @@ Extended error information
>               sock_sendmsg+0x38/0x50
>               ___sys_sendmsg+0x14e/0x270
>      } hitcount:         76
> -    { stacktrace:
> +    { common_stacktrace:
>               netif_rx_internal+0xb2/0xd0
>               netif_rx+0x1c/0x60
>               loopback_xmit+0x6c/0xb0
> @@ -1579,7 +1579,7 @@ Extended error information
>               sock_sendmsg+0x38/0x50
>               ___sys_sendmsg+0x269/0x270
>      } hitcount:         77
> -    { stacktrace:
> +    { common_stacktrace:
>               netif_rx_internal+0xb2/0xd0
>               netif_rx+0x1c/0x60
>               loopback_xmit+0x6c/0xb0
> @@ -1597,7 +1597,7 @@ Extended error information
>               sock_sendmsg+0x38/0x50
>               SYSC_sendto+0xef/0x170
>      } hitcount:         88
> -    { stacktrace:
> +    { common_stacktrace:
>               kernel_clone+0x18e/0x330
>               SyS_clone+0x19/0x20
>               entry_SYSCALL_64_fastpath+0x12/0x6a
> @@ -1949,7 +1949,7 @@ uninterruptible state::
>  
>    # cd /sys/kernel/tracing
>    # echo 's:block_lat pid_t pid; u64 delta; unsigned long[] stack;' > dynamic_events
> -  # echo 'hist:keys=next_pid:ts=common_timestamp.usecs,st=stacktrace  if prev_state == 2' >> events/sched/sched_switch/trigger
> +  # echo 'hist:keys=next_pid:ts=common_timestamp.usecs,st=common_stacktrace  if prev_state == 2' >> events/sched/sched_switch/trigger
>    # echo 'hist:keys=prev_pid:delta=common_timestamp.usecs-$ts,s=$st:onmax($delta).trace(block_lat,prev_pid,$delta,$s)' >> events/sched/sched_switch/trigger
>    # echo 1 > events/synthetic/block_lat/enable
>    # cat trace
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 0e373222a6df..7c4a0b72334e 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -806,6 +806,7 @@ enum {
>  	FILTER_TRACE_FN,
>  	FILTER_COMM,
>  	FILTER_CPU,
> +	FILTER_STACKTRACE,
>  };
>  
>  extern int trace_event_raw_init(struct trace_event_call *call);
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index ebc59781456a..81801dc31784 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5752,7 +5752,7 @@ static const char readme_msg[] =
>  	"\t    table using the key(s) and value(s) named, and the value of a\n"
>  	"\t    sum called 'hitcount' is incremented.  Keys and values\n"
>  	"\t    correspond to fields in the event's format description.  Keys\n"
> -	"\t    can be any field, or the special string 'stacktrace'.\n"
> +	"\t    can be any field, or the special string 'common_stacktrace'.\n"
>  	"\t    Compound keys consisting of up to two fields can be specified\n"
>  	"\t    by the 'keys' keyword.  Values must correspond to numeric\n"
>  	"\t    fields.  Sort keys consisting of up to two fields can be\n"
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 654ffa40457a..57e539d47989 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -194,6 +194,8 @@ static int trace_define_generic_fields(void)
>  	__generic_field(int, common_cpu, FILTER_CPU);
>  	__generic_field(char *, COMM, FILTER_COMM);
>  	__generic_field(char *, comm, FILTER_COMM);
> +	__generic_field(char *, stacktrace, FILTER_STACKTRACE);
> +	__generic_field(char *, STACKTRACE, FILTER_STACKTRACE);
>  
>  	return ret;
>  }
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index 543cb7dc84ad..b97d3ad832f1 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1364,7 +1364,7 @@ static const char *hist_field_name(struct hist_field *field,
>  		if (field->field)
>  			field_name = field->field->name;
>  		else
> -			field_name = "stacktrace";
> +			field_name = "common_stacktrace";
>  	} else if (field->flags & HIST_FIELD_FL_HITCOUNT)
>  		field_name = "hitcount";
>  
> @@ -2367,7 +2367,7 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
>  		hist_data->enable_timestamps = true;
>  		if (*flags & HIST_FIELD_FL_TIMESTAMP_USECS)
>  			hist_data->attrs->ts_in_usecs = true;
> -	} else if (strcmp(field_name, "stacktrace") == 0) {
> +	} else if (strcmp(field_name, "common_stacktrace") == 0) {
>  		*flags |= HIST_FIELD_FL_STACKTRACE;
>  	} else if (strcmp(field_name, "common_cpu") == 0)
>  		*flags |= HIST_FIELD_FL_CPU;
> @@ -2378,11 +2378,15 @@ parse_field(struct hist_trigger_data *hist_data, struct trace_event_file *file,
>  		if (!field || !field->size) {
>  			/*
>  			 * For backward compatibility, if field_name
> -			 * was "cpu", then we treat this the same as
> -			 * common_cpu. This also works for "CPU".
> +			 * was "cpu" or "stacktrace", then we treat this
> +			 * the same as common_cpu and common_stacktrace
> +			 * respectively. This also works for "CPU", and
> +			 * "STACKTRACE".
>  			 */
>  			if (field && field->filter_type == FILTER_CPU) {
>  				*flags |= HIST_FIELD_FL_CPU;
> +			} else if (field && field->filter_type == FILTER_STACKTRACE) {
> +				*flags |= HIST_FIELD_FL_STACKTRACE;
>  			} else {
>  				hist_err(tr, HIST_ERR_FIELD_NOT_FOUND,
>  					 errpos(field_name));
> @@ -5394,7 +5398,7 @@ static void hist_trigger_print_key(struct seq_file *m,
>  			if (key_field->field)
>  				seq_printf(m, "%s.stacktrace", key_field->field->name);
>  			else
> -				seq_puts(m, "stacktrace:\n");
> +				seq_puts(m, "common_stacktrace:\n");
>  			hist_trigger_stacktrace_print(m,
>  						      key + key_field->offset,
>  						      HIST_STACKTRACE_DEPTH);
> @@ -5977,7 +5981,7 @@ static int event_hist_trigger_print(struct seq_file *m,
>  			if (field->field)
>  				seq_printf(m, "%s.stacktrace", field->field->name);
>  			else
> -				seq_puts(m, "stacktrace");
> +				seq_puts(m, "common_stacktrace");
>  		} else
>  			hist_field_print(m, field);
>  	}
> -- 
> 2.39.2
>