On Thu, 18 Dec 2025 10:19:42 -0500 Steven Rostedt <[email protected]> wrote:
> On Mon, 15 Dec 2025 22:13:59 +0100 > Jiri Olsa <[email protected]> wrote: > > > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c > > index 48dc0de5f2ce..95a38fb18ed7 100644 > > --- a/kernel/trace/ftrace.c > > +++ b/kernel/trace/ftrace.c > > @@ -6489,6 +6489,78 @@ int update_ftrace_direct_del(struct ftrace_ops *ops, > > struct ftrace_hash *hash) > > return err; > > } > > > > Kerneldoc needed. > > > +int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash > > *hash, bool do_direct_lock) > > +{ > > + struct ftrace_func_entry *entry, *tmp; > > + static struct ftrace_ops tmp_ops = { > > + .func = ftrace_stub, > > + .flags = FTRACE_OPS_FL_STUB, > > + }; > > + struct ftrace_hash *orig_hash; > > + unsigned long size, i; > > + int err = -EINVAL; > > + > > + if (!hash_count(hash)) > > + return -EINVAL; > > + if (check_direct_multi(ops)) > > + return -EINVAL; > > + if (!(ops->flags & FTRACE_OPS_FL_ENABLED)) > > + return -EINVAL; > > + if (direct_functions == EMPTY_HASH) > > + return -EINVAL; > > + > > + if (do_direct_lock) > > + mutex_lock(&direct_mutex); > > This optional taking of the direct_mutex lock needs some serious rationale > and documentation. > > > + > > + orig_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL; > > + if (!orig_hash) > > + goto unlock; > > + > > + /* Enable the tmp_ops to have the same functions as the direct ops */ Add to the comments here: * In order to modify the direct callers, all the functions need to * first be calling the ftrace_ops_list_func() and not be connected * to any direct callers. To do that, create a temporary ops that * attach to the same functions as the direct ops, and attach that * first. Then when adding the direct ops, it will use the * ftrace_ops_list_func(), and this can safely modify what the * direct ops call. Or something like that. I want this code to be as clear as day to what it is doing. In a year or two, we will forget, and this will be very confusing to newcomers. > > + ftrace_ops_init(&tmp_ops); > > + tmp_ops.func_hash = ops->func_hash; > > + > > + err = register_ftrace_function_nolock(&tmp_ops); > > + if (err) > > + goto unlock; > > + > > + /* > > + * Call __ftrace_hash_update_ipmodify() here, so that we can call > > + * ops->ops_func for the ops. This is needed because the above > > + * register_ftrace_function_nolock() worked on tmp_ops. > > + */ > > + err = __ftrace_hash_update_ipmodify(ops, orig_hash, orig_hash, true); > > + if (err) > > + goto out; > > + > > + /* > > + * Now the ftrace_ops_list_func() is called to do the direct callers. > > + * We can safely change the direct functions attached to each entry. > > + */ > > + mutex_lock(&ftrace_lock); > > I'm going to need some time staring at this code. It looks like it may be > relying on some internals here. > > -- Steve > > > > + I would add a comment here: /* Now update the direct functions to point to the new callbacks */ -- Steve > > + size = 1 << hash->size_bits; > > + for (i = 0; i < size; i++) { > > + hlist_for_each_entry(entry, &hash->buckets[i], hlist) { > > + tmp = __ftrace_lookup_ip(direct_functions, entry->ip); > > + if (!tmp) > > + continue; > > + tmp->direct = entry->direct; > > + } > > + } > > + > > + mutex_unlock(&ftrace_lock); > > + > > +out: > > + /* Removing the tmp_ops will add the updated direct callers to the > > functions */ > > + unregister_ftrace_function(&tmp_ops); > > + > > +unlock: > > + if (do_direct_lock) > > + mutex_unlock(&direct_mutex); > > + return err; > > +} > > + > > #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */ > > > > /**
