[PATCH] tracing: Fix using ret variable in tracing_set_tracer()

[PATCH] tracing: Fix using ret variable in tracing_set_tracer()

[Steven Rostedt]

From: Steven Rostedt <rostedt@goodmis.org>

When the function tracing_set_tracer() switched over to using the guard()
infrastructure, it did not need to save the 'ret' variable and would just
return the value when an error arised, instead of setting ret and jumping
to an out label.

When CONFIG_TRACER_SNAPSHOT is enabled, it had code that expected the
"ret" variable to be initialized to zero and had set 'ret' while holding
an arch_spin_lock() (not used by guard), and then upon releasing the lock
it would check 'ret' and exit if set. But because ret was only set when an
error occurred while holding the locks, 'ret' would be used uninitialized
if there was no error. The code in the CONFIG_TRACER_SNAPSHOT block should
be self contain. Make sure 'ret' is also set when no error occurred.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202412271654.nJVBuwmF-lkp@intel.com/
Fixes: d33b10c0c73ad ("tracing: Switch trace.c code over to use guard()")
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 0aaf442271e9..5aeb898054e7 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -6104,8 +6104,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
 	if (t->use_max_tr) {
 		local_irq_disable();
 		arch_spin_lock(&tr->max_lock);
-		if (tr->cond_snapshot)
-			ret = -EBUSY;
+		ret = tr->cond_snapshot ? -EBUSY : 0;
 		arch_spin_unlock(&tr->max_lock);
 		local_irq_enable();
 		if (ret)
-- 
2.45.2

Re: [PATCH] tracing: Fix using ret variable in tracing_set_tracer()

[Masami Hiramatsu]

On Mon, 6 Jan 2025 11:11:43 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> 
> When the function tracing_set_tracer() switched over to using the guard()
> infrastructure, it did not need to save the 'ret' variable and would just
> return the value when an error arised, instead of setting ret and jumping
> to an out label.
> 
> When CONFIG_TRACER_SNAPSHOT is enabled, it had code that expected the
> "ret" variable to be initialized to zero and had set 'ret' while holding
> an arch_spin_lock() (not used by guard), and then upon releasing the lock
> it would check 'ret' and exit if set. But because ret was only set when an
> error occurred while holding the locks, 'ret' would be used uninitialized
> if there was no error. The code in the CONFIG_TRACER_SNAPSHOT block should
> be self contain. Make sure 'ret' is also set when no error occurred.
> 

Looks good to me.

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

Thanks,

> Reported-by: kernel test robot <lkp@intel.com>
> Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
> Closes: https://lore.kernel.org/r/202412271654.nJVBuwmF-lkp@intel.com/
> Fixes: d33b10c0c73ad ("tracing: Switch trace.c code over to use guard()")
> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  kernel/trace/trace.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 0aaf442271e9..5aeb898054e7 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -6104,8 +6104,7 @@ int tracing_set_tracer(struct trace_array *tr, const char *buf)
>  	if (t->use_max_tr) {
>  		local_irq_disable();
>  		arch_spin_lock(&tr->max_lock);
> -		if (tr->cond_snapshot)
> -			ret = -EBUSY;
> +		ret = tr->cond_snapshot ? -EBUSY : 0;
>  		arch_spin_unlock(&tr->max_lock);
>  		local_irq_enable();
>  		if (ret)
> -- 
> 2.45.2
> 


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