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[PATCH 2/2] tracing: Use switch statement instead of ifs in set_tracer_flag()

Steven Rostedt posted 2 patches 1 month, 1 week ago
[PATCH 2/2] tracing: Use switch statement instead of ifs in set_tracer_flag()
Posted by Steven Rostedt 1 month, 1 week ago 
From: Steven Rostedt <rostedt@goodmis.org>

The "mask" passed in to set_trace_flag() has a single bit set. The
function then checks if the mask is equal to one of the option masks and
performs the appropriate function associated to that option.

Instead of having a bunch of "if ()" statement, use a "switch ()"
statement instead to make it cleaner and a bit more optimal.

No function changes.

Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
---
 kernel/trace/trace.c | 38 +++++++++++++++++++++++---------------
 1 file changed, 23 insertions(+), 15 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 07bd10808277..8460bec9f263 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -5251,11 +5251,13 @@ int trace_keep_overwrite(struct tracer *tracer, u64 mask, int set)
 
 int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
 {
-	if ((mask == TRACE_ITER(RECORD_TGID)) ||
-	    (mask == TRACE_ITER(RECORD_CMD)) ||
-	    (mask == TRACE_ITER(TRACE_PRINTK)) ||
-	    (mask == TRACE_ITER(COPY_MARKER)))
+	switch (mask) {
+	case TRACE_ITER(RECORD_TGID):
+	case TRACE_ITER(RECORD_CMD):
+	case TRACE_ITER(TRACE_PRINTK):
+	case TRACE_ITER(COPY_MARKER):
 		lockdep_assert_held(&event_mutex);
+	}
 
 	/* do nothing if flag is already set */
 	if (!!(tr->trace_flags & mask) == !!enabled)
@@ -5266,7 +5268,8 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
 		if (tr->current_trace->flag_changed(tr, mask, !!enabled))
 			return -EINVAL;
 
-	if (mask == TRACE_ITER(TRACE_PRINTK)) {
+	switch (mask) {
+	case TRACE_ITER(TRACE_PRINTK):
 		if (enabled) {
 			update_printk_trace(tr);
 		} else {
@@ -5283,9 +5286,9 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
 			if (printk_trace == tr)
 				update_printk_trace(&global_trace);
 		}
-	}
+		break;
 
-	if (mask == TRACE_ITER(COPY_MARKER)) {
+	case TRACE_ITER(COPY_MARKER):
 		update_marker_trace(tr, enabled);
 		/* update_marker_trace updates the tr->trace_flags */
 		return 0;
@@ -5296,10 +5299,12 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
 	else
 		tr->trace_flags &= ~mask;
 
-	if (mask == TRACE_ITER(RECORD_CMD))
+	switch (mask) {
+	case TRACE_ITER(RECORD_CMD):
 		trace_event_enable_cmd_record(enabled);
+		break;
 
-	if (mask == TRACE_ITER(RECORD_TGID)) {
+	case TRACE_ITER(RECORD_TGID):
 
 		if (trace_alloc_tgid_map() < 0) {
 			tr->trace_flags &= ~TRACE_ITER(RECORD_TGID);
@@ -5307,24 +5312,27 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
 		}
 
 		trace_event_enable_tgid_record(enabled);
-	}
+		break;
 
-	if (mask == TRACE_ITER(EVENT_FORK))
+	case TRACE_ITER(EVENT_FORK):
 		trace_event_follow_fork(tr, enabled);
+		break;
 
-	if (mask == TRACE_ITER(FUNC_FORK))
+	case TRACE_ITER(FUNC_FORK):
 		ftrace_pid_follow_fork(tr, enabled);
+		break;
 
-	if (mask == TRACE_ITER(OVERWRITE)) {
+	case TRACE_ITER(OVERWRITE):
 		ring_buffer_change_overwrite(tr->array_buffer.buffer, enabled);
 #ifdef CONFIG_TRACER_MAX_TRACE
 		ring_buffer_change_overwrite(tr->max_buffer.buffer, enabled);
 #endif
-	}
+		break;
 
-	if (mask == TRACE_ITER(PRINTK)) {
+	case TRACE_ITER(PRINTK):
 		trace_printk_start_stop_comm(enabled);
 		trace_printk_control(enabled);
+		break;
 	}
 
 	return 0;
-- 
2.51.0
Re: [PATCH 2/2] tracing: Use switch statement instead of ifs in set_tracer_flag()
Posted by Masami Hiramatsu (Google) 1 month, 1 week ago 
On Wed, 05 Nov 2025 19:33:26 -0500
Steven Rostedt <rostedt@kernel.org> wrote:

> From: Steven Rostedt <rostedt@goodmis.org>
> 
> The "mask" passed in to set_trace_flag() has a single bit set. The
> function then checks if the mask is equal to one of the option masks and
> performs the appropriate function associated to that option.
> 
> Instead of having a bunch of "if ()" statement, use a "switch ()"
> statement instead to make it cleaner and a bit more optimal.
> 
> No function changes.
> 

Looks good to me.

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

BTW, set_tracer_flag() seems to expect to modify only one bit.
If we can count the number of its in @mask and reject if it is
not 1, we can use bit-mask instead of the first switch()?

	if (!mask ||	/* mask has no bit */
	    (mask & ~(1 << (ffs64(mask) - 1))))	/* mask has more than 2 bits */
		return -EINVAL;

Thanks,

> Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
> ---
>  kernel/trace/trace.c | 38 +++++++++++++++++++++++---------------
>  1 file changed, 23 insertions(+), 15 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 07bd10808277..8460bec9f263 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -5251,11 +5251,13 @@ int trace_keep_overwrite(struct tracer *tracer, u64 mask, int set)
>  
>  int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
>  {
> -	if ((mask == TRACE_ITER(RECORD_TGID)) ||
> -	    (mask == TRACE_ITER(RECORD_CMD)) ||
> -	    (mask == TRACE_ITER(TRACE_PRINTK)) ||
> -	    (mask == TRACE_ITER(COPY_MARKER)))
> +	switch (mask) {
> +	case TRACE_ITER(RECORD_TGID):
> +	case TRACE_ITER(RECORD_CMD):
> +	case TRACE_ITER(TRACE_PRINTK):
> +	case TRACE_ITER(COPY_MARKER):
>  		lockdep_assert_held(&event_mutex);
> +	}
>  
>  	/* do nothing if flag is already set */
>  	if (!!(tr->trace_flags & mask) == !!enabled)
> @@ -5266,7 +5268,8 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
>  		if (tr->current_trace->flag_changed(tr, mask, !!enabled))
>  			return -EINVAL;
>  
> -	if (mask == TRACE_ITER(TRACE_PRINTK)) {
> +	switch (mask) {
> +	case TRACE_ITER(TRACE_PRINTK):
>  		if (enabled) {
>  			update_printk_trace(tr);
>  		} else {
> @@ -5283,9 +5286,9 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
>  			if (printk_trace == tr)
>  				update_printk_trace(&global_trace);
>  		}
> -	}
> +		break;
>  
> -	if (mask == TRACE_ITER(COPY_MARKER)) {
> +	case TRACE_ITER(COPY_MARKER):
>  		update_marker_trace(tr, enabled);
>  		/* update_marker_trace updates the tr->trace_flags */
>  		return 0;
> @@ -5296,10 +5299,12 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
>  	else
>  		tr->trace_flags &= ~mask;
>  
> -	if (mask == TRACE_ITER(RECORD_CMD))
> +	switch (mask) {
> +	case TRACE_ITER(RECORD_CMD):
>  		trace_event_enable_cmd_record(enabled);
> +		break;
>  
> -	if (mask == TRACE_ITER(RECORD_TGID)) {
> +	case TRACE_ITER(RECORD_TGID):
>  
>  		if (trace_alloc_tgid_map() < 0) {
>  			tr->trace_flags &= ~TRACE_ITER(RECORD_TGID);
> @@ -5307,24 +5312,27 @@ int set_tracer_flag(struct trace_array *tr, u64 mask, int enabled)
>  		}
>  
>  		trace_event_enable_tgid_record(enabled);
> -	}
> +		break;
>  
> -	if (mask == TRACE_ITER(EVENT_FORK))
> +	case TRACE_ITER(EVENT_FORK):
>  		trace_event_follow_fork(tr, enabled);
> +		break;
>  
> -	if (mask == TRACE_ITER(FUNC_FORK))
> +	case TRACE_ITER(FUNC_FORK):
>  		ftrace_pid_follow_fork(tr, enabled);
> +		break;
>  
> -	if (mask == TRACE_ITER(OVERWRITE)) {
> +	case TRACE_ITER(OVERWRITE):
>  		ring_buffer_change_overwrite(tr->array_buffer.buffer, enabled);
>  #ifdef CONFIG_TRACER_MAX_TRACE
>  		ring_buffer_change_overwrite(tr->max_buffer.buffer, enabled);
>  #endif
> -	}
> +		break;
>  
> -	if (mask == TRACE_ITER(PRINTK)) {
> +	case TRACE_ITER(PRINTK):
>  		trace_printk_start_stop_comm(enabled);
>  		trace_printk_control(enabled);
> +		break;
>  	}
>  
>  	return 0;
> -- 
> 2.51.0
> 
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>
Re: [PATCH 2/2] tracing: Use switch statement instead of ifs in set_tracer_flag()
Posted by Steven Rostedt 1 month, 1 week ago 
On Mon, 10 Nov 2025 14:48:26 +0900
Masami Hiramatsu (Google) <mhiramat@kernel.org> wrote:

> BTW, set_tracer_flag() seems to expect to modify only one bit.
> If we can count the number of its in @mask and reject if it is
> not 1, we can use bit-mask instead of the first switch()?
> 
> 	if (!mask ||	/* mask has no bit */
> 	    (mask & ~(1 << (ffs64(mask) - 1))))	/* mask has more than 2 bits */
> 		return -EINVAL;

Well, this has been around for over a decade without any issues. I don't
think a check would be of much use. Not to mention, invalid masks are OK to
pass in.

If anything, I would have liked to pass in the bit number and not a mask.
But that's something we could do another time.

-- Steve

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