Re: [PATCH 2/8] ftrace: Remove the legacy _ftrace_direct API

[Mark Rutland]

On Wed, Feb 01, 2023 at 05:34:14PM +0100, Florent Revest wrote:
> This API relies on a single global ops, used for all direct calls
> registered with it. However, to implement arm64 direct calls, we need
> each ops to point to a single direct call trampoline.
> 
> Signed-off-by: Florent Revest <revest@xxxxxxxxxxxx>
> ---
>  include/linux/ftrace.h |  32 ----
>  kernel/trace/ftrace.c  | 393 -----------------------------------------
>  2 files changed, 425 deletions(-)

Nice diffstat! ;)

Testing on x86_64: this builds cleanly, the FTRACE_STARTUP_TESTS pass, and each
of the ftrace_direct*.ko test modules loads without issue.

So FWIW:

Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Tested-by: Mark Rutland <mark.rutland@xxxxxxx>

Thanks,
Mark.

> 
> diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> index 366c730beaa3..2d7c85e47c2d 100644
> --- a/include/linux/ftrace.h
> +++ b/include/linux/ftrace.h
> @@ -397,14 +397,6 @@ struct ftrace_func_entry {
>  
>  #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
>  extern int ftrace_direct_func_count;
> -int register_ftrace_direct(unsigned long ip, unsigned long addr);
> -int unregister_ftrace_direct(unsigned long ip, unsigned long addr);
> -int modify_ftrace_direct(unsigned long ip, unsigned long old_addr, unsigned long new_addr);
> -struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr);
> -int ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
> -				struct dyn_ftrace *rec,
> -				unsigned long old_addr,
> -				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);
> @@ -414,30 +406,6 @@ int modify_ftrace_direct_multi_nolock(struct ftrace_ops *ops, unsigned long addr
>  #else
>  struct ftrace_ops;
>  # define ftrace_direct_func_count 0
> -static inline int register_ftrace_direct(unsigned long ip, unsigned long addr)
> -{
> -	return -ENOTSUPP;
> -}
> -static inline int unregister_ftrace_direct(unsigned long ip, unsigned long addr)
> -{
> -	return -ENOTSUPP;
> -}
> -static inline int modify_ftrace_direct(unsigned long ip,
> -				       unsigned long old_addr, unsigned long new_addr)
> -{
> -	return -ENOTSUPP;
> -}
> -static inline struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr)
> -{
> -	return NULL;
> -}
> -static inline int ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
> -					      struct dyn_ftrace *rec,
> -					      unsigned long old_addr,
> -					      unsigned long new_addr)
> -{
> -	return -ENODEV;
> -}
>  static inline unsigned long ftrace_find_rec_direct(unsigned long ip)
>  {
>  	return 0;
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index e634b80f49d1..5efe201428fa 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2585,20 +2585,6 @@ static void call_direct_funcs(unsigned long ip, unsigned long pip,
>  
>  	arch_ftrace_set_direct_caller(fregs, addr);
>  }
> -
> -struct ftrace_ops direct_ops = {
> -	.func		= call_direct_funcs,
> -	.flags		= FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS
> -			  | FTRACE_OPS_FL_PERMANENT,
> -	/*
> -	 * By declaring the main trampoline as this trampoline
> -	 * it will never have one allocated for it. Allocated
> -	 * trampolines should not call direct functions.
> -	 * The direct_ops should only be called by the builtin
> -	 * ftrace_regs_caller trampoline.
> -	 */
> -	.trampoline	= FTRACE_REGS_ADDR,
> -};
>  #endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
>  
>  /**
> @@ -5295,387 +5281,8 @@ struct ftrace_direct_func {
>  
>  static LIST_HEAD(ftrace_direct_funcs);
>  
> -/**
> - * ftrace_find_direct_func - test an address if it is a registered direct caller
> - * @addr: The address of a registered direct caller
> - *
> - * This searches to see if a ftrace direct caller has been registered
> - * at a specific address, and if so, it returns a descriptor for it.
> - *
> - * This can be used by architecture code to see if an address is
> - * a direct caller (trampoline) attached to a fentry/mcount location.
> - * This is useful for the function_graph tracer, as it may need to
> - * do adjustments if it traced a location that also has a direct
> - * trampoline attached to it.
> - */
> -struct ftrace_direct_func *ftrace_find_direct_func(unsigned long addr)
> -{
> -	struct ftrace_direct_func *entry;
> -	bool found = false;
> -
> -	/* May be called by fgraph trampoline (protected by rcu tasks) */
> -	list_for_each_entry_rcu(entry, &ftrace_direct_funcs, next) {
> -		if (entry->addr == addr) {
> -			found = true;
> -			break;
> -		}
> -	}
> -	if (found)
> -		return entry;
> -
> -	return NULL;
> -}
> -
> -static struct ftrace_direct_func *ftrace_alloc_direct_func(unsigned long addr)
> -{
> -	struct ftrace_direct_func *direct;
> -
> -	direct = kmalloc(sizeof(*direct), GFP_KERNEL);
> -	if (!direct)
> -		return NULL;
> -	direct->addr = addr;
> -	direct->count = 0;
> -	list_add_rcu(&direct->next, &ftrace_direct_funcs);
> -	ftrace_direct_func_count++;
> -	return direct;
> -}
> -
>  static int register_ftrace_function_nolock(struct ftrace_ops *ops);
>  
> -/**
> - * register_ftrace_direct - Call a custom trampoline directly
> - * @ip: The address of the nop at the beginning of a function
> - * @addr: The address of the trampoline to call at @ip
> - *
> - * This is used to connect a direct call from the nop location (@ip)
> - * at the start of ftrace traced functions. The location that it calls
> - * (@addr) must be able to handle a direct call, and save the parameters
> - * of the function being traced, and restore them (or inject new ones
> - * if needed), before returning.
> - *
> - * Returns:
> - *  0 on success
> - *  -EBUSY - Another direct function is already attached (there can be only one)
> - *  -ENODEV - @ip does not point to a ftrace nop location (or not supported)
> - *  -ENOMEM - There was an allocation failure.
> - */
> -int register_ftrace_direct(unsigned long ip, unsigned long addr)
> -{
> -	struct ftrace_direct_func *direct;
> -	struct ftrace_func_entry *entry;
> -	struct ftrace_hash *free_hash = NULL;
> -	struct dyn_ftrace *rec;
> -	int ret = -ENODEV;
> -
> -	mutex_lock(&direct_mutex);
> -
> -	ip = ftrace_location(ip);
> -	if (!ip)
> -		goto out_unlock;
> -
> -	/* See if there's a direct function at @ip already */
> -	ret = -EBUSY;
> -	if (ftrace_find_rec_direct(ip))
> -		goto out_unlock;
> -
> -	ret = -ENODEV;
> -	rec = lookup_rec(ip, ip);
> -	if (!rec)
> -		goto out_unlock;
> -
> -	/*
> -	 * Check if the rec says it has a direct call but we didn't
> -	 * find one earlier?
> -	 */
> -	if (WARN_ON(rec->flags & FTRACE_FL_DIRECT))
> -		goto out_unlock;
> -
> -	/* Make sure the ip points to the exact record */
> -	if (ip != rec->ip) {
> -		ip = rec->ip;
> -		/* Need to check this ip for a direct. */
> -		if (ftrace_find_rec_direct(ip))
> -			goto out_unlock;
> -	}
> -
> -	ret = -ENOMEM;
> -	direct = ftrace_find_direct_func(addr);
> -	if (!direct) {
> -		direct = ftrace_alloc_direct_func(addr);
> -		if (!direct)
> -			goto out_unlock;
> -	}
> -
> -	entry = ftrace_add_rec_direct(ip, addr, &free_hash);
> -	if (!entry)
> -		goto out_unlock;
> -
> -	ret = ftrace_set_filter_ip(&direct_ops, ip, 0, 0);
> -
> -	if (!ret && !(direct_ops.flags & FTRACE_OPS_FL_ENABLED)) {
> -		ret = register_ftrace_function_nolock(&direct_ops);
> -		if (ret)
> -			ftrace_set_filter_ip(&direct_ops, ip, 1, 0);
> -	}
> -
> -	if (ret) {
> -		remove_hash_entry(direct_functions, entry);
> -		kfree(entry);
> -		if (!direct->count) {
> -			list_del_rcu(&direct->next);
> -			synchronize_rcu_tasks();
> -			kfree(direct);
> -			if (free_hash)
> -				free_ftrace_hash(free_hash);
> -			free_hash = NULL;
> -			ftrace_direct_func_count--;
> -		}
> -	} else {
> -		direct->count++;
> -	}
> - out_unlock:
> -	mutex_unlock(&direct_mutex);
> -
> -	if (free_hash) {
> -		synchronize_rcu_tasks();
> -		free_ftrace_hash(free_hash);
> -	}
> -
> -	return ret;
> -}
> -EXPORT_SYMBOL_GPL(register_ftrace_direct);
> -
> -static struct ftrace_func_entry *find_direct_entry(unsigned long *ip,
> -						   struct dyn_ftrace **recp)
> -{
> -	struct ftrace_func_entry *entry;
> -	struct dyn_ftrace *rec;
> -
> -	rec = lookup_rec(*ip, *ip);
> -	if (!rec)
> -		return NULL;
> -
> -	entry = __ftrace_lookup_ip(direct_functions, rec->ip);
> -	if (!entry) {
> -		WARN_ON(rec->flags & FTRACE_FL_DIRECT);
> -		return NULL;
> -	}
> -
> -	WARN_ON(!(rec->flags & FTRACE_FL_DIRECT));
> -
> -	/* Passed in ip just needs to be on the call site */
> -	*ip = rec->ip;
> -
> -	if (recp)
> -		*recp = rec;
> -
> -	return entry;
> -}
> -
> -int unregister_ftrace_direct(unsigned long ip, unsigned long addr)
> -{
> -	struct ftrace_direct_func *direct;
> -	struct ftrace_func_entry *entry;
> -	struct ftrace_hash *hash;
> -	int ret = -ENODEV;
> -
> -	mutex_lock(&direct_mutex);
> -
> -	ip = ftrace_location(ip);
> -	if (!ip)
> -		goto out_unlock;
> -
> -	entry = find_direct_entry(&ip, NULL);
> -	if (!entry)
> -		goto out_unlock;
> -
> -	hash = direct_ops.func_hash->filter_hash;
> -	if (hash->count == 1)
> -		unregister_ftrace_function(&direct_ops);
> -
> -	ret = ftrace_set_filter_ip(&direct_ops, ip, 1, 0);
> -
> -	WARN_ON(ret);
> -
> -	remove_hash_entry(direct_functions, entry);
> -
> -	direct = ftrace_find_direct_func(addr);
> -	if (!WARN_ON(!direct)) {
> -		/* This is the good path (see the ! before WARN) */
> -		direct->count--;
> -		WARN_ON(direct->count < 0);
> -		if (!direct->count) {
> -			list_del_rcu(&direct->next);
> -			synchronize_rcu_tasks();
> -			kfree(direct);
> -			kfree(entry);
> -			ftrace_direct_func_count--;
> -		}
> -	}
> - out_unlock:
> -	mutex_unlock(&direct_mutex);
> -
> -	return ret;
> -}
> -EXPORT_SYMBOL_GPL(unregister_ftrace_direct);
> -
> -static struct ftrace_ops stub_ops = {
> -	.func		= ftrace_stub,
> -};
> -
> -/**
> - * ftrace_modify_direct_caller - modify ftrace nop directly
> - * @entry: The ftrace hash entry of the direct helper for @rec
> - * @rec: The record representing the function site to patch
> - * @old_addr: The location that the site at @rec->ip currently calls
> - * @new_addr: The location that the site at @rec->ip should call
> - *
> - * An architecture may overwrite this function to optimize the
> - * changing of the direct callback on an ftrace nop location.
> - * This is called with the ftrace_lock mutex held, and no other
> - * ftrace callbacks are on the associated record (@rec). Thus,
> - * it is safe to modify the ftrace record, where it should be
> - * currently calling @old_addr directly, to call @new_addr.
> - *
> - * This is called with direct_mutex locked.
> - *
> - * Safety checks should be made to make sure that the code at
> - * @rec->ip is currently calling @old_addr. And this must
> - * also update entry->direct to @new_addr.
> - */
> -int __weak ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
> -				       struct dyn_ftrace *rec,
> -				       unsigned long old_addr,
> -				       unsigned long new_addr)
> -{
> -	unsigned long ip = rec->ip;
> -	int ret;
> -
> -	lockdep_assert_held(&direct_mutex);
> -
> -	/*
> -	 * The ftrace_lock was used to determine if the record
> -	 * had more than one registered user to it. If it did,
> -	 * we needed to prevent that from changing to do the quick
> -	 * switch. But if it did not (only a direct caller was attached)
> -	 * then this function is called. But this function can deal
> -	 * with attached callers to the rec that we care about, and
> -	 * since this function uses standard ftrace calls that take
> -	 * the ftrace_lock mutex, we need to release it.
> -	 */
> -	mutex_unlock(&ftrace_lock);
> -
> -	/*
> -	 * By setting a stub function at the same address, we force
> -	 * the code to call the iterator and the direct_ops helper.
> -	 * This means that @ip does not call the direct call, and
> -	 * we can simply modify it.
> -	 */
> -	ret = ftrace_set_filter_ip(&stub_ops, ip, 0, 0);
> -	if (ret)
> -		goto out_lock;
> -
> -	ret = register_ftrace_function_nolock(&stub_ops);
> -	if (ret) {
> -		ftrace_set_filter_ip(&stub_ops, ip, 1, 0);
> -		goto out_lock;
> -	}
> -
> -	entry->direct = new_addr;
> -
> -	/*
> -	 * By removing the stub, we put back the direct call, calling
> -	 * the @new_addr.
> -	 */
> -	unregister_ftrace_function(&stub_ops);
> -	ftrace_set_filter_ip(&stub_ops, ip, 1, 0);
> -
> - out_lock:
> -	mutex_lock(&ftrace_lock);
> -
> -	return ret;
> -}
> -
> -/**
> - * modify_ftrace_direct - Modify an existing direct call to call something else
> - * @ip: The instruction pointer to modify
> - * @old_addr: The address that the current @ip calls directly
> - * @new_addr: The address that the @ip should call
> - *
> - * This modifies a ftrace direct caller at an instruction pointer without
> - * having to disable it first. The direct call will switch over to the
> - * @new_addr without missing anything.
> - *
> - * Returns: zero on success. Non zero on error, which includes:
> - *  -ENODEV : the @ip given has no direct caller attached
> - *  -EINVAL : the @old_addr does not match the current direct caller
> - */
> -int modify_ftrace_direct(unsigned long ip,
> -			 unsigned long old_addr, unsigned long new_addr)
> -{
> -	struct ftrace_direct_func *direct, *new_direct = NULL;
> -	struct ftrace_func_entry *entry;
> -	struct dyn_ftrace *rec;
> -	int ret = -ENODEV;
> -
> -	mutex_lock(&direct_mutex);
> -
> -	mutex_lock(&ftrace_lock);
> -
> -	ip = ftrace_location(ip);
> -	if (!ip)
> -		goto out_unlock;
> -
> -	entry = find_direct_entry(&ip, &rec);
> -	if (!entry)
> -		goto out_unlock;
> -
> -	ret = -EINVAL;
> -	if (entry->direct != old_addr)
> -		goto out_unlock;
> -
> -	direct = ftrace_find_direct_func(old_addr);
> -	if (WARN_ON(!direct))
> -		goto out_unlock;
> -	if (direct->count > 1) {
> -		ret = -ENOMEM;
> -		new_direct = ftrace_alloc_direct_func(new_addr);
> -		if (!new_direct)
> -			goto out_unlock;
> -		direct->count--;
> -		new_direct->count++;
> -	} else {
> -		direct->addr = new_addr;
> -	}
> -
> -	/*
> -	 * If there's no other ftrace callback on the rec->ip location,
> -	 * then it can be changed directly by the architecture.
> -	 * If there is another caller, then we just need to change the
> -	 * direct caller helper to point to @new_addr.
> -	 */
> -	if (ftrace_rec_count(rec) == 1) {
> -		ret = ftrace_modify_direct_caller(entry, rec, old_addr, new_addr);
> -	} else {
> -		entry->direct = new_addr;
> -		ret = 0;
> -	}
> -
> -	if (unlikely(ret && new_direct)) {
> -		direct->count++;
> -		list_del_rcu(&new_direct->next);
> -		synchronize_rcu_tasks();
> -		kfree(new_direct);
> -		ftrace_direct_func_count--;
> -	}
> -
> - out_unlock:
> -	mutex_unlock(&ftrace_lock);
> -	mutex_unlock(&direct_mutex);
> -	return ret;
> -}
> -EXPORT_SYMBOL_GPL(modify_ftrace_direct);
> -
>  #define MULTI_FLAGS (FTRACE_OPS_FL_DIRECT | FTRACE_OPS_FL_SAVE_REGS)
>  
>  static int check_direct_multi(struct ftrace_ops *ops)
> -- 
> 2.39.1.519.gcb327c4b5f-goog
>