On Tue, 31 Aug 2021 11:50:16 +0200
Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> Adding interface to modify registered direct function
> for ftrace_ops. Adding following function:
>
> modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
>
> The function changes the currently registered direct
> function for all attached functions.
>
> Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
> ---
> include/linux/ftrace.h | 6 ++++++
> kernel/trace/ftrace.c | 43 ++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 49 insertions(+)
>
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index e40b5201c16e..f3ba6366f7af 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -318,6 +318,8 @@ int ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
> unsigned long ftrace_find_rec_direct(unsigned long ip);
> int register_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr);
> int unregister_ftrace_direct_multi(struct ftrace_ops *ops);
> +int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr);
> +
> #else
> struct ftrace_ops;
> # define ftrace_direct_func_count 0
> @@ -357,6 +359,10 @@ static inline int unregister_ftrace_direct_multi(struct ftrace_ops *ops)
> {
> return -ENODEV;
> }
> +static inline int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
> +{
> + return -ENODEV;
> +}
> #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
>
> #ifndef CONFIG_HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 7243769493c9..59940a6a907c 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -5518,6 +5518,49 @@ int unregister_ftrace_direct_multi(struct ftrace_ops *ops)
> return err;
> }
> EXPORT_SYMBOL_GPL(unregister_ftrace_direct_multi);
> +
Needs kernel doc comments.
> +int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
> +{
> + struct ftrace_hash *hash = ops->func_hash->filter_hash;
> + struct ftrace_func_entry *entry, *iter;
> + int i, size;
> + int err;
> +
> + if (check_direct_multi(ops))
> + return -EINVAL;
> + if (!(ops->flags & FTRACE_OPS_FL_ENABLED))
> + return -EINVAL;
> +
> + mutex_lock(&direct_mutex);
> + mutex_lock(&ftrace_lock);
> +
> + /*
> + * Shutdown the ops, change 'direct' pointer for each
> + * ops entry in direct_functions hash and startup the
> + * ops back again.
> + */
> + err = ftrace_shutdown(ops, 0);
This needs to be commented that there's going to be a rather large time
frame that there will be no callbacks happening while this update occurs.
A better solution, that prevents having to do this, is to first change
the function fentry's to call the ftrace list loop function, that calls
the ftrace_ops list, and will call the direct call via the ops in the
loop. Have the ops->func call the new direct function (all will be
immediately affected). Update the entries, and then switch from the
loop back to the direct caller.
-- Steve
> + if (err)
> + goto out_unlock;
> +
> + size = 1 << hash->size_bits;
> + for (i = 0; i < size; i++) {
> + hlist_for_each_entry(iter, &hash->buckets[i], hlist) {
> + entry = __ftrace_lookup_ip(direct_functions, iter->ip);
> + if (!entry)
> + continue;
> + entry->direct = addr;
> + }
> + }
> +
> + err = ftrace_startup(ops, 0);
> +
> + out_unlock:
> + mutex_unlock(&ftrace_lock);
> + mutex_unlock(&direct_mutex);
> + return err;
> +}
> +EXPORT_SYMBOL_GPL(modify_ftrace_direct_multi);
> #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
>
> /**
