ftrace: Add update_ftrace_direct_del function

Adding update_ftrace_direct_del function that removes all entries
(ip -> addr) provided in hash argument to direct ftrace ops and
updates its attachments.

The difference to current unregister_ftrace_direct is
 - hash argument that allows to unregister multiple ip -> direct
   entries at once
 - we can call update_ftrace_direct_del multiple times on the
   same ftrace_ops object, becase we do not need to unregister
   all entries at once, we can do it gradualy with the help of
   ftrace_update_ops function

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>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/bpf/20251230145010.103439-6-jolsa@kernel.org

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 43a6cfaf5aae437967948ee9320ea047a23081fe..cfb957731433a3e5c81a5a8563fe1541f6cf5019 100644 (file)
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -544,6 +544,7 @@ int modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr);
 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);
 
 void ftrace_stub_direct_tramp(void);
 
@@ -576,6 +577,11 @@ static inline int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace
        return -ENODEV;
 }
 
+static inline int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
+{
+       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 97bd988b0a62f3a4fc60e93ddac10219158e7066..244bb7553d3dfb9dba1982ac54a4f2a107eae2c2 100644 (file)
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -6418,6 +6418,133 @@ int update_ftrace_direct_add(struct ftrace_ops *ops, struct ftrace_hash *hash)
        return err;
 }
 
+/**
+ * hash_sub - substracts @b from @a and returns the result
+ * @a: struct ftrace_hash object
+ * @b: struct ftrace_hash object
+ *
+ * Returns struct ftrace_hash object on success, NULL on error.
+ */
+static struct ftrace_hash *hash_sub(struct ftrace_hash *a, struct ftrace_hash *b)
+{
+       struct ftrace_func_entry *entry, *del;
+       struct ftrace_hash *sub;
+       int size;
+
+       sub = alloc_and_copy_ftrace_hash(a->size_bits, a);
+       if (!sub)
+               return NULL;
+
+       size = 1 << b->size_bits;
+       for (int i = 0; i < size; i++) {
+               hlist_for_each_entry(entry, &b->buckets[i], hlist) {
+                       del = __ftrace_lookup_ip(sub, entry->ip);
+                       if (WARN_ON_ONCE(!del)) {
+                               free_ftrace_hash(sub);
+                               return NULL;
+                       }
+                       remove_hash_entry(sub, del);
+                       kfree(del);
+               }
+       }
+       return sub;
+}
+
+/**
+ * update_ftrace_direct_del - Updates @ops by removing its direct
+ * callers provided in @hash
+ * @ops: The address of the struct ftrace_ops object
+ * @hash: The address of the struct ftrace_hash object
+ *
+ * This is used to delete custom direct callers (ip -> addr) in
+ * @ops specified via @hash. The @ops will be either unregistered
+ * updated.
+ *
+ * Returns: zero on success. Non zero on error, which includes:
+ *  -EINVAL - The @hash is empty
+ *  -EINVAL - The @ops is not registered
+ */
+int update_ftrace_direct_del(struct ftrace_ops *ops, struct ftrace_hash *hash)
+{
+       struct ftrace_hash *old_direct_functions = NULL;
+       struct ftrace_hash *new_direct_functions;
+       struct ftrace_hash *new_filter_hash = NULL;
+       struct ftrace_hash *old_filter_hash;
+       struct ftrace_func_entry *entry;
+       struct ftrace_func_entry *del;
+       unsigned long size;
+       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;
+
+       mutex_lock(&direct_mutex);
+
+       old_filter_hash = ops->func_hash ? ops->func_hash->filter_hash : NULL;
+
+       if (!hash_count(old_filter_hash))
+               goto out_unlock;
+
+       /* Make sure requested entries are already registered. */
+       size = 1 << hash->size_bits;
+       for (int i = 0; i < size; i++) {
+               hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
+                       del = __ftrace_lookup_ip(direct_functions, entry->ip);
+                       if (!del || del->direct != entry->direct)
+                               goto out_unlock;
+               }
+       }
+
+       err = -ENOMEM;
+       new_filter_hash = hash_sub(old_filter_hash, hash);
+       if (!new_filter_hash)
+               goto out_unlock;
+
+       new_direct_functions = hash_sub(direct_functions, hash);
+       if (!new_direct_functions)
+               goto out_unlock;
+
+       /* If there's nothing left, we need to unregister the ops. */
+       if (ftrace_hash_empty(new_filter_hash)) {
+               err = unregister_ftrace_function(ops);
+               if (!err) {
+                       /* cleanup for possible another register call */
+                       ops->func = NULL;
+                       ops->trampoline = 0;
+                       ftrace_free_filter(ops);
+                       ops->func_hash->filter_hash = NULL;
+               }
+       } else {
+               err = ftrace_update_ops(ops, new_filter_hash, EMPTY_HASH);
+               /*
+                * new_filter_hash is dup-ed, so we need to release it anyway,
+                * old_filter_hash either stays on error or is already released
+                */
+       }
+
+       if (err) {
+               /* free the new_direct_functions */
+               old_direct_functions = new_direct_functions;
+       } else {
+               rcu_assign_pointer(direct_functions, new_direct_functions);
+       }
+
+ out_unlock:
+       mutex_unlock(&direct_mutex);
+
+       if (old_direct_functions && old_direct_functions != EMPTY_HASH)
+               call_rcu_tasks(&old_direct_functions->rcu, register_ftrace_direct_cb);
+       free_ftrace_hash(new_filter_hash);
+
+       return err;
+}
+
 #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
 
 /**