Adding update_ftrace_direct_mod function that modifies all entries
(ip -> direct) provided in hash argument to direct ftrace ops and
updates its attachments.
The difference to current modify_ftrace_direct is:
- hash argument that allows to modify multiple ip -> direct
entries at once
This change will allow us to have simple ftrace_ops for all bpf
direct interface users in following changes.
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
include/linux/ftrace.h | 6 ++++
kernel/trace/ftrace.c | 72 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 78 insertions(+)
diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index ac4b473c7fd3..c3bf9cede1fe 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -545,6 +545,7 @@ int modify_ftrace_direct_nolock(struct ftrace_ops *ops, unsigned long addr);
int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace_hash *hash);
int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash);
+int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock);
void ftrace_stub_direct_tramp(void);
@@ -582,6 +583,11 @@ static inline int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace
return -ENODEV;
}
+static inline int update_ftrace_direct_mod(struct ftrace_ops *ops, struct ftrace_hash *hash, bool do_direct_lock)
+{
+ return -ENODEV;
+}
+
/*
* This must be implemented by the architecture.
* It is the way the ftrace direct_ops helper, when called
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;
}
+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);
+
+ 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 */
+ 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);
+
+ 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 */
/**
--
2.52.0On Mon, 15 Dec 2025 22:13:59 +0100
Jiri Olsa <jolsa@kernel.org> 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 */
> + 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
> +
> + 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 */
>
> /**
On Thu, Dec 18, 2025 at 10:19:42AM -0500, Steven Rostedt wrote:
> On Mon, 15 Dec 2025 22:13:59 +0100
> Jiri Olsa <jolsa@kernel.org> 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.
will add
>
> > +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.
it mirrors the use of modify_ftrace_direct/modify_ftrace_direct_nolock
when we do trampoline update from within ftrace_ops->ops_func callback
I'll add comments with more details
>
> > +
> > + 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 */
> > + 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.
ok, thanks
jirka
On Thu, 18 Dec 2025 10:19:42 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:
> On Mon, 15 Dec 2025 22:13:59 +0100
> Jiri Olsa <jolsa@kernel.org> 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 */
> >
> > /**
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