Re: [PATCH bpf] ftrace: fix incorrect hash size in register_ftrace_direct()

[Steven Rostedt]

On Sat, 12 Apr 2025 21:33:48 +0800
Menglong Dong <menglong8.dong@xxxxxxxxx> wrote:

> The max ftrace hash bits is made fls(32) in register_ftrace_direct(),
> which seems illogical, and it seems to be a spelling mistake.
> 
> Just fix it.
> 
> (Do I misunderstand something?)

I think the logic is incorrect and this patch doesn't fix it.

> 
> Fixes: d05cb470663a ("ftrace: Fix modification of direct_function hash while in use")
> Signed-off-by: Menglong Dong <dongml2@xxxxxxxxxxxxxxx>
> ---
>  kernel/trace/ftrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 1a48aedb5255..7697605a41e6 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5914,7 +5914,7 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr)
>  
>  	/* Make a copy hash to place the new and the old entries in */
>  	size = hash->count + direct_functions->count;
> -	if (size > 32)
> +	if (size < 32)
>  		size = 32;
>  	new_hash = alloc_ftrace_hash(fls(size));
>  	if (!new_hash)

The above probably should be:

	size = hash->count + direct_functions->count
	size = fls(size);
	if (size > FTRACE_HASH_MAX_BITS)
                size = FTRACE_HASH_MAX_BITS;
	new_hash = alloc_ftrace_hash(size);

-- Steve