[PATCH 1/7] ftrace: Let unregister_ftrace_direct_multi() call ftrace_free_filter()

Florent Revest
2023-03-16T17:38:42Z

A common pattern when using the ftrace_direct_multi API is to unregister
the ops and also immediately free its filter. We've noticed it's very
easy for users to miss calling ftrace_free_filter().

This adds a "free_filters" argument to unregister_ftrace_direct_multi()
to both remind the user they should free filters and also to make their
life easier.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Florent Revest <revest@chromium.org>
---
include/linux/ftrace.h | 6 ++++--
kernel/bpf/trampoline.c | 2 +-
kernel/trace/ftrace.c | 6 +++++-
samples/ftrace/ftrace-direct-multi-modify.c | 3 +--
samples/ftrace/ftrace-direct-multi.c | 3 +--
5 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 366c730beaa3..5b68ee874bc1 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -407,7 +407,8 @@ int ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
unsigned long new_addr);
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, unsigned long addr);
+int unregister_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr,
+ bool free_filters);
int modify_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr);
int modify_ftrace_direct_multi_nolock(struct ftrace_ops *ops, unsigned long addr);

@@ -446,7 +447,8 @@ static inline int register_ftrace_direct_multi(struct ftrace_ops *ops, unsigned
{
return -ENODEV;
}
-static inline int unregister_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
+static inline int unregister_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr,
+ bool free_filters)
{
return -ENODEV;
}
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index d0ed7d6f5eec..88bc23f1e10a 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -198,7 +198,7 @@ static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
int ret;

if (tr->func.ftrace_managed)
- ret = unregister_ftrace_direct_multi(tr->fops, (long)old_addr);
+ ret = unregister_ftrace_direct_multi(tr->fops, (long)old_addr, false);
else
ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, old_addr, NULL);

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 29baa97d0d53..fa379cf91fdb 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5804,7 +5804,8 @@ EXPORT_SYMBOL_GPL(register_ftrace_direct_multi);
* 0 on success
* -EINVAL - The @ops object was not properly registered.
*/
-int unregister_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
+int unregister_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr,
+ bool free_filters)
{
struct ftrace_hash *hash = ops->func_hash->filter_hash;
int err;
@@ -5822,6 +5823,9 @@ int unregister_ftrace_direct_multi(struct ftrace_ops *ops, unsigned long addr)
/* cleanup for possible another register call */
ops->func = NULL;
ops->trampoline = 0;
+
+ if (free_filters)
+ ftrace_free_filter(ops);
return err;
}
EXPORT_SYMBOL_GPL(unregister_ftrace_direct_multi);
diff --git a/samples/ftrace/ftrace-direct-multi-modify.c b/samples/ftrace/ftrace-direct-multi-modify.c
index b58c594efb51..196b43971cb5 100644
--- a/samples/ftrace/ftrace-direct-multi-modify.c
+++ b/samples/ftrace/ftrace-direct-multi-modify.c
@@ -151,8 +151,7 @@ static int __init ftrace_direct_multi_init(void)
static void __exit ftrace_direct_multi_exit(void)
{
kthread_stop(simple_tsk);
- unregister_ftrace_direct_multi(&direct, my_tramp);
- ftrace_free_filter(&direct);
+ unregister_ftrace_direct_multi(&direct, my_tramp, true);
}

module_init(ftrace_direct_multi_init);
diff --git a/samples/ftrace/ftrace-direct-multi.c b/samples/ftrace/ftrace-direct-multi.c
index c27cf130c319..ea0e88ee5e43 100644
--- a/samples/ftrace/ftrace-direct-multi.c
+++ b/samples/ftrace/ftrace-direct-multi.c
@@ -78,8 +78,7 @@ static int __init ftrace_direct_multi_init(void)

static void __exit ftrace_direct_multi_exit(void)
{
- unregister_ftrace_direct_multi(&direct, (unsigned long) my_tramp);
- ftrace_free_filter(&direct);
+ unregister_ftrace_direct_multi(&direct, (unsigned long) my_tramp, true);
}

module_init(ftrace_direct_multi_init);
--
2.40.0.rc2.332.ga46443480c-goog