[2/2] trace-cmd: Check if ftrace file exists, before writing in it.
diff mbox series

Message ID 20191018145759.15335-2-tz.stoyanov@gmail.com
State Accepted
Commit 113b0664003c8287793875acd6199e5b4d7aa80d
Headers show
Series
  • [1/2] trace-cmd: Fix a crash on "trace-cmd reset" command
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Commit Message

Tzvetomir Stoyanov (VMware) Oct. 18, 2019, 2:57 p.m. UTC
Depending of the kernel configuration, some ftrace files are optional
and may not exist. This should not confuse trace-cmd, as it is a valid
case. One such case is tracing_max_latency file, when CONFIG_TRACER_MAX_TRACE
or CONFIG_HWLAT_TRACER are not set.
A check is added in write_instance_file() to ensure the file exist before trying
to write in it.

https://bugzilla.kernel.org/show_bug.cgi?id=205241

Reported-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 tracecmd/trace-record.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Steven Rostedt Oct. 18, 2019, 3:18 p.m. UTC | #1
On Fri, 18 Oct 2019 17:57:59 +0300
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:

> ---
>  tracecmd/trace-record.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> index 81aca1f..c65731f 100644
> --- a/tracecmd/trace-record.c
> +++ b/tracecmd/trace-record.c
> @@ -813,11 +813,14 @@ static int
>  write_instance_file(struct buffer_instance *instance,
>  		    const char *file, const char *str, const char *type)
>  {
> +	struct stat st;
>  	char *path;
>  	int ret;
>  
>  	path = get_instance_file(instance, file);
> -	ret = write_file(path, str, type);
> +	ret = stat(path, &st);

This is fine for now, but perhaps in the future we should check if it
is writable by the user. Hmm, we could move that check to the
write_file() itself. But that will require changing other locations
that expect write_file() to die. Which in the long run, we want to
remove that assumption.

Thanks for the patch, I just applied it.

-- Steve

> +	if (ret == 0)
> +		ret = write_file(path, str, type);
>  	tracecmd_put_tracing_file(path);
>  
>  	return ret;
Valentin Schneider Oct. 18, 2019, 3:20 p.m. UTC | #2
Hi Tzvetomir,

On 18/10/2019 15:57, Tzvetomir Stoyanov (VMware) wrote:
> Depending of the kernel configuration, some ftrace files are optional
> and may not exist. This should not confuse trace-cmd, as it is a valid
> case. One such case is tracing_max_latency file, when CONFIG_TRACER_MAX_TRACE
> or CONFIG_HWLAT_TRACER are not set.
> A check is added in write_instance_file() to ensure the file exist before trying
> to write in it.
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=205241
> 
> Reported-by: Valentin Schneider <valentin.schneider@arm.com>
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>

Ran through my test just fine, so:

Tested-by: Valentin Schneider <valentin.schneider@arm.com>

Thanks for looking at this!

> ---
>  tracecmd/trace-record.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
> index 81aca1f..c65731f 100644
> --- a/tracecmd/trace-record.c
> +++ b/tracecmd/trace-record.c
> @@ -813,11 +813,14 @@ static int
>  write_instance_file(struct buffer_instance *instance,
>  		    const char *file, const char *str, const char *type)
>  {
> +	struct stat st;
>  	char *path;
>  	int ret;
>  
>  	path = get_instance_file(instance, file);
> -	ret = write_file(path, str, type);
> +	ret = stat(path, &st);
> +	if (ret == 0)
> +		ret = write_file(path, str, type);
>  	tracecmd_put_tracing_file(path);
>  
>  	return ret;
>

Patch
diff mbox series

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 81aca1f..c65731f 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -813,11 +813,14 @@  static int
 write_instance_file(struct buffer_instance *instance,
 		    const char *file, const char *str, const char *type)
 {
+	struct stat st;
 	char *path;
 	int ret;
 
 	path = get_instance_file(instance, file);
-	ret = write_file(path, str, type);
+	ret = stat(path, &st);
+	if (ret == 0)
+		ret = write_file(path, str, type);
 	tracecmd_put_tracing_file(path);
 
 	return ret;