tracing: Use kstrdup_const() for constant hist field type

[PATCH] tracing: Use kstrdup_const() for constant hist field type

Posted by Yu Peng 1 week, 6 days ago

The HIST_FIELD_FL_CONST path duplicates the literal "u64" type with
kstrdup(), then releases it through kfree_const().

Use kstrdup_const() instead, avoiding the allocation for a .rodata string
while keeping the matching free helper.

Signed-off-by: Yu Peng <pengyu@kylinos.cn>
---
 kernel/trace/trace_events_hist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index eb2c2bc8bc3d..6ffe9f4720a0 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1992,7 +1992,7 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 	if (flags & HIST_FIELD_FL_CONST) {
 		hist_field->fn_num = HIST_FIELD_FN_CONST;
 		hist_field->size = sizeof(u64);
-		hist_field->type = kstrdup("u64", GFP_KERNEL);
+		hist_field->type = kstrdup_const("u64", GFP_KERNEL);
 		if (!hist_field->type)
 			goto free;
 		goto out;
-- 
2.43.0

Re: [PATCH] tracing: Use kstrdup_const() for constant hist field type

Posted by Masami Hiramatsu (Google) 1 week, 5 days ago

On Tue, 26 May 2026 17:51:05 +0800
Yu Peng <pengyu@kylinos.cn> wrote:

> The HIST_FIELD_FL_CONST path duplicates the literal "u64" type with
> kstrdup(), then releases it through kfree_const().
> 
> Use kstrdup_const() instead, avoiding the allocation for a .rodata string
> while keeping the matching free helper.
> 

Since we are using kfree_const() to free hist_field->type,
we can just point it as same as HIST_FIELD_FL_HITCOUNT case.

Thanks,

> Signed-off-by: Yu Peng <pengyu@kylinos.cn>
> ---
>  kernel/trace/trace_events_hist.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index eb2c2bc8bc3d..6ffe9f4720a0 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1992,7 +1992,7 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
>  	if (flags & HIST_FIELD_FL_CONST) {
>  		hist_field->fn_num = HIST_FIELD_FN_CONST;
>  		hist_field->size = sizeof(u64);
> -		hist_field->type = kstrdup("u64", GFP_KERNEL);
> +		hist_field->type = kstrdup_const("u64", GFP_KERNEL);
>  		if (!hist_field->type)
>  			goto free;
>  		goto out;
> -- 
> 2.43.0


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

Re: [PATCH] tracing: Use kstrdup_const() for constant hist field type

Posted by Steven Rostedt 1 week, 5 days ago

On Wed, 27 May 2026 10:10:15 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> On Tue, 26 May 2026 17:51:05 +0800
> Yu Peng <pengyu@kylinos.cn> wrote:
> 
> > The HIST_FIELD_FL_CONST path duplicates the literal "u64" type with
> > kstrdup(), then releases it through kfree_const().
> > 
> > Use kstrdup_const() instead, avoiding the allocation for a .rodata string
> > while keeping the matching free helper.
> >   
> 
> Since we are using kfree_const() to free hist_field->type,
> we can just point it as same as HIST_FIELD_FL_HITCOUNT case.
> 

Agreed.

> Thanks,
> 
> > Signed-off-by: Yu Peng <pengyu@kylinos.cn>
> > ---
> >  kernel/trace/trace_events_hist.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> > index eb2c2bc8bc3d..6ffe9f4720a0 100644
> > --- a/kernel/trace/trace_events_hist.c
> > +++ b/kernel/trace/trace_events_hist.c
> > @@ -1992,7 +1992,7 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
> >  	if (flags & HIST_FIELD_FL_CONST) {
> >  		hist_field->fn_num = HIST_FIELD_FN_CONST;
> >  		hist_field->size = sizeof(u64);
> > -		hist_field->type = kstrdup("u64", GFP_KERNEL);
> > +		hist_field->type = kstrdup_const("u64", GFP_KERNEL);

This can simply be made to point to "u64".

Thanks,

-- Steve

> >  		if (!hist_field->type)
> >  			goto free;
> >  		goto out;
> > -- 
> > 2.43.0  
> 
>

[PATCH v2] tracing: Point constant hist field type to string literal

Posted by Yu Peng 1 week, 5 days ago

The HIST_FIELD_FL_CONST path uses the fixed "u64" type string.

Point hist_field->type directly to the string literal, matching the
HIST_FIELD_FL_HITCOUNT path. The release path already uses kfree_const(),
so no duplication is needed.

Signed-off-by: Yu Peng <pengyu@kylinos.cn>
---
Changes in v2:
- Point hist_field->type directly to "u64" as suggested.

 kernel/trace/trace_events_hist.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index eb2c2bc8bc3d5..b50f2bd5ff771 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -1992,9 +1992,7 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
 	if (flags & HIST_FIELD_FL_CONST) {
 		hist_field->fn_num = HIST_FIELD_FN_CONST;
 		hist_field->size = sizeof(u64);
-		hist_field->type = kstrdup("u64", GFP_KERNEL);
-		if (!hist_field->type)
-			goto free;
+		hist_field->type = "u64";
 		goto out;
 	}
 
-- 
2.43.0

Re: [PATCH v2] tracing: Point constant hist field type to string literal

Posted by Steven Rostedt 1 week, 5 days ago

On Wed, 27 May 2026 10:18:27 +0800
Yu Peng <pengyu@kylinos.cn> wrote:

> The HIST_FIELD_FL_CONST path uses the fixed "u64" type string.
> 
> Point hist_field->type directly to the string literal, matching the
> HIST_FIELD_FL_HITCOUNT path. The release path already uses kfree_const(),
> so no duplication is needed.
> 
> Signed-off-by: Yu Peng <pengyu@kylinos.cn>
> ---
> Changes in v2:
> - Point hist_field->type directly to "u64" as suggested

All new versions of a patch need to start a new thread. Please resend
this as a new thread and not a reply.

-- Steve


> 
>  kernel/trace/trace_events_hist.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
> index eb2c2bc8bc3d5..b50f2bd5ff771 100644
> --- a/kernel/trace/trace_events_hist.c
> +++ b/kernel/trace/trace_events_hist.c
> @@ -1992,9 +1992,7 @@ static struct hist_field *create_hist_field(struct hist_trigger_data *hist_data,
>  	if (flags & HIST_FIELD_FL_CONST) {
>  		hist_field->fn_num = HIST_FIELD_FN_CONST;
>  		hist_field->size = sizeof(u64);
> -		hist_field->type = kstrdup("u64", GFP_KERNEL);
> -		if (!hist_field->type)
> -			goto free;
> +		hist_field->type = "u64";
>  		goto out;
>  	}
>