fgraph: Allocate ret_stack_list with proper size

Commit Message

Steven Rostedt Oct. 19, 2024, 1:52 a.m. UTC

From: Steven Rostedt <[e-mail]>

The ret_stack_list is an array of ret_stack shadow stacks for the function
graph usage. When the first function graph is enabled, all tasks in the
system get a shadow stack. The ret_stack_list is a 32 element array of
pointers to these shadow stacks. It allocates the shadow stack in batches
(32 stacks at a time), assigns them to running tasks, and continues until
all tasks are covered.

When the function graph shadow stack changed from an array of
ftrace_ret_stack structures to an array of longs, the allocation of
ret_stack_list went from allocating an array of 32 elements to just a
block defined by SHADOW_STACK_SIZE. Luckily, that's defined as PAGE_SIZE
and is much more than enough to hold 32 pointers. But it is way overkill
for the amount needed to allocate.

Change the allocation of ret_stack_list back to a kcalloc() of
FTRACE_RETSTACK_ALLOC_SIZE pointers.

Fixes: 42675b723b484 ("function_graph: Convert ret_stack to a series of longs")
Signed-off-by: Steven Rostedt (Google) <[e-mail]>
---
 kernel/trace/fgraph.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Comments

Masami Hiramatsu (Google) Oct. 21, 2024, 7:43 a.m. UTC | #1

On Fri, 18 Oct 2024 21:52:12 -0400
Steven Rostedt <[e-mail]> wrote:

> From: Steven Rostedt <[e-mail]>
> 
> The ret_stack_list is an array of ret_stack shadow stacks for the function
> graph usage. When the first function graph is enabled, all tasks in the
> system get a shadow stack. The ret_stack_list is a 32 element array of
> pointers to these shadow stacks. It allocates the shadow stack in batches
> (32 stacks at a time), assigns them to running tasks, and continues until
> all tasks are covered.
> 
> When the function graph shadow stack changed from an array of
> ftrace_ret_stack structures to an array of longs, the allocation of
> ret_stack_list went from allocating an array of 32 elements to just a
> block defined by SHADOW_STACK_SIZE. Luckily, that's defined as PAGE_SIZE
> and is much more than enough to hold 32 pointers. But it is way overkill
> for the amount needed to allocate.
> 
> Change the allocation of ret_stack_list back to a kcalloc() of
> FTRACE_RETSTACK_ALLOC_SIZE pointers.

Looks good to me.

Acked-by: Masami Hiramatsu (Google) <[e-mail]>

Thanks,

> 
> Fixes: 42675b723b484 ("function_graph: Convert ret_stack to a series of longs")
> Signed-off-by: Steven Rostedt (Google) <[e-mail]>
> ---
>  kernel/trace/fgraph.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
> index 43f4e3f57438..41e7a15dcb50 100644
> --- a/kernel/trace/fgraph.c
> +++ b/kernel/trace/fgraph.c
> @@ -1162,7 +1162,8 @@ static int start_graph_tracing(void)
>  	unsigned long **ret_stack_list;
>  	int ret;
>  
> -	ret_stack_list = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
> +	ret_stack_list = kcalloc(FTRACE_RETSTACK_ALLOC_SIZE,
> +				 sizeof(*ret_stack_list), GFP_KERNEL);
>  
>  	if (!ret_stack_list)
>  		return -ENOMEM;
> -- 
> 2.45.2
>

Patch

diff --git a/kernel/trace/fgraph.c b/kernel/trace/fgraph.c
index 43f4e3f57438..41e7a15dcb50 100644
--- a/kernel/trace/fgraph.c
+++ b/kernel/trace/fgraph.c
@@ -1162,7 +1162,8 @@  static int start_graph_tracing(void)
 	unsigned long **ret_stack_list;
 	int ret;
 
-	ret_stack_list = kmalloc(SHADOW_STACK_SIZE, GFP_KERNEL);
+	ret_stack_list = kcalloc(FTRACE_RETSTACK_ALLOC_SIZE,
+				 sizeof(*ret_stack_list), GFP_KERNEL);
 
 	if (!ret_stack_list)
 		return -ENOMEM;