Re: [PATCHv6 bpf-next 9/9] bpf,x86: Use single ftrace_ops for direct calls

[Ihor Solodrai <ihor.solodrai@linux.dev>]

On 2/27/26 1:24 PM, Jiri Olsa wrote:
> On Fri, Feb 27, 2026 at 09:37:52PM +0100, Jiri Olsa wrote:
>> [...]
>>
>>>
>>>     With CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS ftrace_replace_code()
>>>     operates on all call sites in the shared ops. Then if a concurrent
>>>     ftrace user (like kprobe) modifies a call site in between
>>>     ftrace_replace_code's verify pass and its patch pass, then ftrace_bug
>>>     fires and sets ftrace_disabled to 1.
>>
>> hum, I'd think that's all under ftrace_lock/direct_mutex,
>> but we might be missing some paths
>>
> 
> could you please try with change below? I can no longer trigger the bug with it

Can confirm that the bug doesn't trigger with this change.
At least by the reproducer test.

Tested-by: Ihor Solodrai <ihor.solodrai@linux.dev>

Thanks!

> 
> thanks,
> jirka
> 
> 
> ---
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 827fb9a0bf0d..e333749a5896 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -6404,7 +6404,9 @@ int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace_hash *hash)
>  			new_filter_hash = old_filter_hash;
>  		}
>  	} else {
> +		mutex_lock(&ftrace_lock);
>  		err = ftrace_update_ops(ops, new_filter_hash, EMPTY_HASH);
> +		mutex_unlock(&ftrace_lock);
>  		/*
>  		 * new_filter_hash is dup-ed, so we need to release it anyway,
>  		 * old_filter_hash either stays on error or is already released
> @@ -6530,7 +6532,9 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
>  			ops->func_hash->filter_hash = NULL;
>  		}
>  	} else {
> +		mutex_lock(&ftrace_lock);
>  		err = ftrace_update_ops(ops, new_filter_hash, EMPTY_HASH);
> +		mutex_unlock(&ftrace_lock);
>  		/*
>  		 * new_filter_hash is dup-ed, so we need to release it anyway,
>  		 * old_filter_hash either stays on error or is already released