[PATCH 1/2] tracing/wakeup: Balance prolog on fgraph failure

[PATCH 1/2] tracing/wakeup: Balance prolog on fgraph failure

[Sasha Levin]

Commit a485ea9e3ef3 ("tracing: Fix irqsoff and wakeup latency tracers when
using function graph") added fgraph_reserve_data()/fgraph_retrieve_data() to
the wakeup tracer's function-graph hooks.

When func_prolog_preempt_disable() succeeded but those calls failed, the code
returned without undoing the prolog (no local_dec(&data->disabled), no
preempt_enable_notrace()). That leaked a preempt disable into later code and
could trigger "BUG: scheduling while atomic".

Balance the prolog on these failure paths in both entry and return hooks.

Fixes: a485ea9e3ef3 ("tracing: Fix irqsoff and wakeup latency tracers when using function graph")
Assisted-by: gpt-5-codex
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_sched_wakeup.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index bf1cb80742aed..fa48bbdf0851c 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -138,8 +138,11 @@ static int wakeup_graph_entry(struct ftrace_graph_ent *trace,
 		return 0;
 
 	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
-	if (!calltime)
+	if (!calltime) {
+		local_dec(&data->disabled);
+		preempt_enable_notrace();
 		return 0;
+	}
 
 	*calltime = trace_clock_local();
 
@@ -169,8 +172,11 @@ static void wakeup_graph_return(struct ftrace_graph_ret *trace,
 	rettime = trace_clock_local();
 
 	calltime = fgraph_retrieve_data(gops->idx, &size);
-	if (!calltime)
+	if (!calltime) {
+		local_dec(&data->disabled);
+		preempt_enable_notrace();
 		return;
+	}
 
 	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
 	local_dec(&data->disabled);
-- 
2.51.0

[PATCH 2/2] tracing/irqsoff: Balance prolog on fgraph failure

[Sasha Levin]

Commit a485ea9e3ef3 ("tracing: Fix irqsoff and wakeup latency tracers when
using function graph") added fgraph_reserve_data()/fgraph_retrieve_data() to
the irqsoff tracer's function-graph hooks.

When func_prolog_dec() succeeded but those calls failed, the code returned
without undoing the prolog (no local_dec(&data->disabled)). While
func_prolog_dec() does not disable preemption, this left the tracer recursion
guard (data->disabled) incremented on this CPU, suppressing subsequent tracing
and leaving the tracer state inconsistent.

Balance the prolog on these failure paths in both entry and return hooks.

Fixes: a485ea9e3ef3 ("tracing: Fix irqsoff and wakeup latency tracers when using function graph")
Assisted-by: gpt-5-codex
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 kernel/trace/trace_irqsoff.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 5496758b6c760..39152ef3d2432 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -202,8 +202,10 @@ static int irqsoff_graph_entry(struct ftrace_graph_ent *trace,
 		return 0;
 
 	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
-	if (!calltime)
+	if (!calltime) {
+		local_dec(&data->disabled);
 		return 0;
+	}
 
 	*calltime = trace_clock_local();
 
@@ -233,8 +235,10 @@ static void irqsoff_graph_return(struct ftrace_graph_ret *trace,
 
 	rettime = trace_clock_local();
 	calltime = fgraph_retrieve_data(gops->idx, &size);
-	if (!calltime)
+	if (!calltime) {
+		local_dec(&data->disabled);
 		return;
+	}
 
 	trace_ctx = tracing_gen_ctx_flags(flags);
 	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
-- 
2.51.0

Re: [PATCH 1/2] tracing/wakeup: Balance prolog on fgraph failure

[Steven Rostedt]

On Mon,  6 Oct 2025 13:58:47 -0400
Sasha Levin <sashal@kernel.org> wrote:

> diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
> index bf1cb80742aed..fa48bbdf0851c 100644
> --- a/kernel/trace/trace_sched_wakeup.c
> +++ b/kernel/trace/trace_sched_wakeup.c
> @@ -138,8 +138,11 @@ static int wakeup_graph_entry(struct ftrace_graph_ent *trace,
>  		return 0;
>  
>  	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
> -	if (!calltime)
> +	if (!calltime) {
> +		local_dec(&data->disabled);
> +		preempt_enable_notrace();
>  		return 0;
> +	}
>  
>  	*calltime = trace_clock_local();
>  
> @@ -169,8 +172,11 @@ static void wakeup_graph_return(struct ftrace_graph_ret *trace,
>  	rettime = trace_clock_local();
>  
>  	calltime = fgraph_retrieve_data(gops->idx, &size);
> -	if (!calltime)
> +	if (!calltime) {
> +		local_dec(&data->disabled);
> +		preempt_enable_notrace();
>  		return;
> +	}
>  
>  	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
>  	local_dec(&data->disabled);

Technically correct, but this would look better:

diff --git a/kernel/trace/trace_sched_wakeup.c b/kernel/trace/trace_sched_wakeup.c
index bf1cb80742ae..e3f2e4f56faa 100644
--- a/kernel/trace/trace_sched_wakeup.c
+++ b/kernel/trace/trace_sched_wakeup.c
@@ -138,12 +138,10 @@ static int wakeup_graph_entry(struct ftrace_graph_ent *trace,
 		return 0;
 
 	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
-	if (!calltime)
-		return 0;
-
-	*calltime = trace_clock_local();
-
-	ret = __trace_graph_entry(tr, trace, trace_ctx);
+	if (calltime) {
+		*calltime = trace_clock_local();
+		ret = __trace_graph_entry(tr, trace, trace_ctx);
+	}
 	local_dec(&data->disabled);
 	preempt_enable_notrace();
 
@@ -169,12 +167,10 @@ static void wakeup_graph_return(struct ftrace_graph_ret *trace,
 	rettime = trace_clock_local();
 
 	calltime = fgraph_retrieve_data(gops->idx, &size);
-	if (!calltime)
-		return;
+	if (calltime)
+		__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
 
-	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
 	local_dec(&data->disabled);
-
 	preempt_enable_notrace();
 	return;
 }


-- Steve

Re: [PATCH 2/2] tracing/irqsoff: Balance prolog on fgraph failure

[Steven Rostedt]

On Mon,  6 Oct 2025 13:58:48 -0400
Sasha Levin <sashal@kernel.org> wrote:

> diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
> index 5496758b6c760..39152ef3d2432 100644
> --- a/kernel/trace/trace_irqsoff.c
> +++ b/kernel/trace/trace_irqsoff.c
> @@ -202,8 +202,10 @@ static int irqsoff_graph_entry(struct ftrace_graph_ent *trace,
>  		return 0;
>  
>  	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
> -	if (!calltime)
> +	if (!calltime) {
> +		local_dec(&data->disabled);
>  		return 0;
> +	}
>  
>  	*calltime = trace_clock_local();
>  
> @@ -233,8 +235,10 @@ static void irqsoff_graph_return(struct ftrace_graph_ret *trace,
>  
>  	rettime = trace_clock_local();
>  	calltime = fgraph_retrieve_data(gops->idx, &size);
> -	if (!calltime)
> +	if (!calltime) {
> +		local_dec(&data->disabled);
>  		return;
> +	}
>  
>  	trace_ctx = tracing_gen_ctx_flags(flags);
>  	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
> -- 

Technically correct, but this would look better:

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 5496758b6c76..4c45c49b06c8 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -184,7 +184,7 @@ static int irqsoff_graph_entry(struct ftrace_graph_ent *trace,
 	unsigned long flags;
 	unsigned int trace_ctx;
 	u64 *calltime;
-	int ret;
+	int ret = 0;
 
 	if (ftrace_graph_ignore_func(gops, trace))
 		return 0;
@@ -202,13 +202,11 @@ static int irqsoff_graph_entry(struct ftrace_graph_ent *trace,
 		return 0;
 
 	calltime = fgraph_reserve_data(gops->idx, sizeof(*calltime));
-	if (!calltime)
-		return 0;
-
-	*calltime = trace_clock_local();
-
-	trace_ctx = tracing_gen_ctx_flags(flags);
-	ret = __trace_graph_entry(tr, trace, trace_ctx);
+	if (calltime) {
+		*calltime = trace_clock_local();
+		trace_ctx = tracing_gen_ctx_flags(flags);
+		ret = __trace_graph_entry(tr, trace, trace_ctx);
+	}
 	local_dec(&data->disabled);
 
 	return ret;
@@ -233,11 +231,10 @@ static void irqsoff_graph_return(struct ftrace_graph_ret *trace,
 
 	rettime = trace_clock_local();
 	calltime = fgraph_retrieve_data(gops->idx, &size);
-	if (!calltime)
-		return;
-
-	trace_ctx = tracing_gen_ctx_flags(flags);
-	__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
+	if (calltime) {
+		trace_ctx = tracing_gen_ctx_flags(flags);
+		__trace_graph_return(tr, trace, trace_ctx, *calltime, rettime);
+	}
 	local_dec(&data->disabled);
 }
 
-- Steve