Message-ID: <20240328173357.517fbf2a@gandalf.local.home>
Date: Thu, 28 Mar 2024 17:33:57 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Sicheng Liu <lsc2001@...look.com>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
 linux-doc@...r.kernel.org, mhiramat@...nel.org,
 mathieu.desnoyers@...icios.com, corbet@....net
Subject: Re: [RFC PATCH 1/2] tracing: Introduce stack filter for trace
 events

On Thu, 25 Jan 2024 06:50:21 +0000
Sicheng Liu <lsc2001@...look.com> wrote:

Sorry for the late reply, this got missed in a flood of other patches, not
to mention it was sent when I was very behind and probably just skipped it
for "todo later". Well, it's later ;-)

> Stack filter can be used to filter event call stacks,
> so that only those trace events whose call stacks match the
> stack filters can appear in the trace output.
> 
> A new config "CONFIG_TRACE_EVENT_STACK_FILTER" is added, if
> enabled, "stack_filter" will be created under the directory
> of a trace event. Stack filters can be set by writing or
> append to it with format "'!'?((function|'**')'/')*(function|'**')".
> A new file "trace_events_stack_filter.c" is added also.
> 
> Signed-off-by: Sicheng Liu <lsc2001@...look.com>
> ---
>  include/linux/trace_events.h             |  39 ++
>  kernel/trace/Kconfig                     |  12 +
>  kernel/trace/Makefile                    |   3 +
>  kernel/trace/trace.c                     |   9 +-
>  kernel/trace/trace.h                     |  10 +
>  kernel/trace/trace_events.c              |  14 +
>  kernel/trace/trace_events_stack_filter.c | 840 +++++++++++++++++++++++
>  7 files changed, 925 insertions(+), 2 deletions(-)
>  create mode 100644 kernel/trace/trace_events_stack_filter.c
> 
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index d68ff9b1247f..fe138b5b6e52 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -250,6 +250,19 @@ int trace_output_call(struct trace_iterator *iter, char *name, char *fmt, ...)
>  
>  struct event_filter;
>  
> +#define STACK_FILTER_ADDR_MAP_SIZE 31
> +
> +/* A cache to speed up addr_remove_offset */
> +struct stack_filter_addr_map {
> +	struct hlist_head map[STACK_FILTER_ADDR_MAP_SIZE];
> +	spinlock_t lock;
> +};
> +
> +struct event_stack_filter {
> +	struct list_head filters;
> +	struct stack_filter_addr_map *addr_map;
> +};
> +
>  enum trace_reg {
>  	TRACE_REG_REGISTER,
>  	TRACE_REG_UNREGISTER,
> @@ -493,6 +506,7 @@ enum {
>  	EVENT_FILE_FL_PID_FILTER_BIT,
>  	EVENT_FILE_FL_WAS_ENABLED_BIT,
>  	EVENT_FILE_FL_FREED_BIT,
> +	EVENT_FILE_FL_STACK_FILTER_BIT,
>  };
>  
>  extern struct trace_event_file *trace_get_event_file(const char *instance,
> @@ -646,12 +660,16 @@ enum {
>  	EVENT_FILE_FL_PID_FILTER	= (1 << EVENT_FILE_FL_PID_FILTER_BIT),
>  	EVENT_FILE_FL_WAS_ENABLED	= (1 << EVENT_FILE_FL_WAS_ENABLED_BIT),
>  	EVENT_FILE_FL_FREED		= (1 << EVENT_FILE_FL_FREED_BIT),
> +	EVENT_FILE_FL_STACK_FILTER	= (1 << EVENT_FILE_FL_STACK_FILTER_BIT),
>  };
>  
>  struct trace_event_file {
>  	struct list_head		list;
>  	struct trace_event_call		*event_call;
>  	struct event_filter __rcu	*filter;
> +#ifdef CONFIG_TRACE_EVENT_STACK_FILTER
> +	struct event_stack_filter __rcu	*stack_filter;
> +#endif
>  	struct eventfs_inode		*ei;
>  	struct trace_array		*tr;
>  	struct trace_subsystem_dir	*system;
> @@ -717,6 +735,27 @@ enum event_trigger_type {
>  
>  extern int filter_match_preds(struct event_filter *filter, void *rec);
>  
> +#ifdef CONFIG_TRACE_EVENT_STACK_FILTER
> +extern int stack_filter_match(struct event_stack_filter *stack_filter);
> +
> +static inline struct event_stack_filter *
> +get_stack_filter(struct trace_event_file *file)
> +{
> +	return rcu_dereference(file->stack_filter);
> +}
> +#else
> +static inline int stack_filter_match(struct event_stack_filter *stack_filter)
> +{
> +	return 1;
> +}
> +
> +static inline struct event_stack_filter *
> +get_stack_filter(struct trace_event_file *file)
> +{
> +	return NULL;
> +}
> +#endif // CONFIG_TRACE_EVENT_STACK_FILTER
> +
>  extern enum event_trigger_type
>  event_triggers_call(struct trace_event_file *file,
>  		    struct trace_buffer *buffer, void *rec,
> diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> index 61c541c36596..2ce5c769e0c1 100644
> --- a/kernel/trace/Kconfig
> +++ b/kernel/trace/Kconfig
> @@ -1169,6 +1169,18 @@ config HIST_TRIGGERS_DEBUG
>  
>            If unsure, say N.
>  
> +config TRACE_EVENT_STACK_FILTER
> +	bool "Enable call stack filter for trace events"
> +	default n
> +	depends on STACKTRACE
> +	depends on KALLSYMS
> +	help
> +	  This option enables call stack filter for trace events,
> +	  so that only those trace events whose call stacks match the
> +	  stack filter can appear in the trace output.
> +
> +	  See Documentation/trace/events.rst for details.
> +

This should be set right after "Enable uprobes-based dynamic events" as the
bottom of the tracing config menu is mostly for testing options.


>  source "kernel/trace/rv/Kconfig"
>  
>  endif # FTRACE
> diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> index 057cd975d014..6deeb9bffa8b 100644
> --- a/kernel/trace/Makefile
> +++ b/kernel/trace/Makefile
> @@ -82,6 +82,9 @@ obj-$(CONFIG_EVENT_TRACING) += trace_event_perf.o
>  endif
>  obj-$(CONFIG_EVENT_TRACING) += trace_events_filter.o
>  obj-$(CONFIG_EVENT_TRACING) += trace_events_trigger.o
> +ifeq ($(CONFIG_TRACE_EVENT_STACK_FILTER),y)
> +obj-$(CONFIG_EVENT_TRACING) += trace_events_stack_filter.o
> +endif
>  obj-$(CONFIG_PROBE_EVENTS) += trace_eprobe.o
>  obj-$(CONFIG_TRACE_EVENT_INJECT) += trace_events_inject.o
>  obj-$(CONFIG_SYNTH_EVENTS) += trace_events_synth.o
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 2a7c6fd934e9..aead7c8111e6 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -2842,8 +2842,8 @@ trace_event_buffer_lock_reserve(struct trace_buffer **current_rb,
>  
>  	*current_rb = tr->array_buffer.buffer;
>  
> -	if (!tr->no_filter_buffering_ref &&
> -	    (trace_file->flags & (EVENT_FILE_FL_SOFT_DISABLED | EVENT_FILE_FL_FILTERED))) {
> +	if (!tr->no_filter_buffering_ref && (trace_file->flags &
> +	    (EVENT_FILE_FL_SOFT_DISABLED | EVENT_FILE_FL_FILTERED | EVENT_FILE_FL_STACK_FILTER))) {
>  		preempt_disable_notrace();
>  		/*
>  		 * Filtering is on, so try to use the per cpu buffer first.
> @@ -2939,6 +2939,11 @@ static void output_printk(struct trace_event_buffer *fbuffer)
>  	     !filter_match_preds(file->filter, fbuffer->entry)))
>  		return;
>  
> +	if (IS_ENABLED(CONFIG_TRACE_EVENT_STACK_FILTER) &&
> +	    unlikely(file->flags & EVENT_FILE_FL_STACK_FILTER) &&
> +	    !stack_filter_match(get_stack_filter(file)))
> +		return;
> +
>  	event = &fbuffer->trace_file->event_call->event;
>  
>  	raw_spin_lock_irqsave(&tracepoint_iter_lock, flags);
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 00f873910c5d..5986bb871343 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -1423,6 +1423,7 @@ __event_trigger_test_discard(struct trace_event_file *file,
>  
>  	if (likely(!(file->flags & (EVENT_FILE_FL_SOFT_DISABLED |
>  				    EVENT_FILE_FL_FILTERED |
> +				    EVENT_FILE_FL_STACK_FILTER |
>  				    EVENT_FILE_FL_PID_FILTER))))
>  		return false;
>  
> @@ -1433,6 +1434,11 @@ __event_trigger_test_discard(struct trace_event_file *file,
>  	    !filter_match_preds(file->filter, entry))
>  		goto discard;
>  
> +	if (IS_ENABLED(CONFIG_TRACE_EVENT_STACK_FILTER) &&
> +	    (file->flags & EVENT_FILE_FL_STACK_FILTER) &&
> +	    !stack_filter_match(get_stack_filter(file)))
> +		goto discard;

This should be add at the end as the other filters should take precedence
(as they are more common).

> +
>  	if ((file->flags & EVENT_FILE_FL_PID_FILTER) &&
>  	    trace_event_ignore_this_pid(file))
>  		goto discard;
> @@ -1562,6 +1568,10 @@ static inline void *event_file_data(struct file *filp)
>  extern struct mutex event_mutex;
>  extern struct list_head ftrace_events;
>  
> +#ifdef CONFIG_TRACE_EVENT_STACK_FILTER
> +extern const struct file_operations event_stack_filter_fops;
> +#endif
> +
>  extern const struct file_operations event_trigger_fops;
>  extern const struct file_operations event_hist_fops;
>  extern const struct file_operations event_hist_debug_fops;
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 7c364b87352e..3647205f3c48 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -2502,6 +2502,14 @@ static int event_callback(const char *name, umode_t *mode, void **data,
>  			*fops = &ftrace_event_filter_fops;
>  			return 1;
>  		}
> +
> +#ifdef CONFIG_TRACE_EVENT_STACK_FILTER
> +		if (strcmp(name, "stack_filter") == 0) {
> +			*mode = TRACE_MODE_WRITE;
> +			*fops = &event_stack_filter_fops;
> +			return 1;
> +		}
> +#endif
>  	}
>  
>  	if (!(call->flags & TRACE_EVENT_FL_IGNORE_ENABLE) ||
> @@ -2598,6 +2606,12 @@ event_create_dir(struct eventfs_inode *parent, struct trace_event_file *file)
>  			.name		= "inject",
>  			.callback	= event_callback,
>  		},
> +#endif
> +#ifdef CONFIG_TRACE_EVENT_STACK_FILTER
> +		{
> +			.name		= "stack_filter",
> +			.callback	= event_callback,
> +		},
>  #endif
>  	};
>  
> diff --git a/kernel/trace/trace_events_stack_filter.c b/kernel/trace/trace_events_stack_filter.c
> new file mode 100644
> index 000000000000..79ed9af853ec
> --- /dev/null
> +++ b/kernel/trace/trace_events_stack_filter.c
> @@ -0,0 +1,840 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * trace_events_stack_filter: call stack filter for trace events
> + *
> + * Copyright (C) 2024 Sicheng Liu <lsc2001@...look.com>
> + */
> +
> +#include <linux/mutex.h>
> +#include <linux/slab.h>
> +
> +#include "trace.h"
> +
> +#define PARSER_BUF_SIZE 1023	/* trace parser buf size */
> +#define STACK_BUF_SIZE 512	/* call stack buf size */
> +
> +#define MAX_SF_LEN 64		/* max stack filter length */
> +#define DSTARS_ADDR 1		/* '**' wildcard */
> +
> +#define list_length(head) ({ \
> +	int __len = 0; \
> +	struct list_head *__pos; \
> +	list_for_each(__pos, head) \
> +		__len++; \
> +	__len; \
> +})
> +
> +#define ADDR_MAP_HASH(key) \
> +	(((key) >> 2) % STACK_FILTER_ADDR_MAP_SIZE)
> +
> +struct function_address {
> +	struct list_head list;
> +	size_t addr;			/* some addresses may represent wildcards */
> +};
> +
> +struct stack_filter {
> +	struct list_head list;
> +	char *string;			/* original string */
> +	struct list_head addrs;		/* function addresses */
> +	bool neg;			/* negate the filter */
> +};
> +
> +struct addr_map_node {
> +	struct hlist_node node;
> +	unsigned long key;
> +	unsigned long value;
> +};
> +
> +static inline void
> +function_address_list_clear(struct list_head *faddrs)
> +{
> +	struct function_address *faddr, *tmp;
> +
> +	list_for_each_entry_safe(faddr, tmp, faddrs, list) {
> +		list_del(&faddr->list);
> +		kfree(faddr);
> +	}
> +}
> +
> +static inline int
> +function_address_list_copy(struct list_head *copy, struct list_head *faddrs)
> +{
> +	struct function_address *faddr, *new_faddr;
> +
> +	INIT_LIST_HEAD(copy);
> +	list_for_each_entry_reverse(faddr, faddrs, list) {
> +		new_faddr = kmalloc(sizeof(*new_faddr), GFP_KERNEL);
> +		if (!new_faddr) {
> +			function_address_list_clear(copy);
> +			return -ENOMEM;
> +		}
> +		new_faddr->addr = faddr->addr;
> +		list_add(&new_faddr->list, copy);
> +	}
> +	return 0;
> +}
> +
> +static inline void
> +stack_filter_init(struct stack_filter *filter)

Unless the init function is going to be used in more than one place, just
do the initialization where the allocation is.

> +{
> +	INIT_LIST_HEAD(&filter->addrs);
> +}
> +
> +static inline struct stack_filter *
> +stack_filter_new(void)
> +{
> +	struct stack_filter *filter;
> +
> +	filter = kzalloc(sizeof(*filter), GFP_KERNEL);
> +	if (!filter)
> +		return NULL;
> +
> +	stack_filter_init(filter);
> +	return filter;
> +}
> +
> +static inline void
> +stack_filter_free(struct stack_filter *filter)
> +{
> +	struct function_address *faddr, *tmp;
> +
> +	list_for_each_entry_safe(faddr, tmp, &filter->addrs, list) {
> +		list_del(&faddr->list);
> +		kfree(faddr);
> +	}
> +
> +	kfree(filter->string);
> +	kfree(filter);
> +}
> +
> +static inline int
> +stack_filter_copy(struct stack_filter *copy, struct stack_filter *filter)
> +{
> +	int ret = 0;
> +
> +	copy->string = kstrdup(filter->string, GFP_KERNEL);
> +	if (!copy->string)
> +		return -ENOMEM;
> +
> +	ret = function_address_list_copy(&copy->addrs, &filter->addrs);
> +	if (ret < 0) {
> +		kfree(copy->string);
> +		return ret;
> +	}
> +
> +	copy->neg = filter->neg;
> +	return 0;
> +}
> +
> +static inline void
> +stack_filter_list_clear(struct list_head *filters)
> +{
> +	struct stack_filter *filter, *tmp;
> +
> +	list_for_each_entry_safe(filter, tmp, filters, list) {
> +		list_del(&filter->list);
> +		stack_filter_free(filter);
> +	}
> +}
> +
> +static inline int
> +stack_filter_list_copy(struct list_head *copy, struct list_head *filters)
> +{
> +	int ret = 0;
> +	struct stack_filter *filter, *new_filter;
> +
> +	/* merge initialization with copy */
> +	INIT_LIST_HEAD(copy);
> +	list_for_each_entry_reverse(filter, filters, list) {
> +		new_filter = kmalloc(sizeof(*new_filter), GFP_KERNEL);
> +		if (!new_filter) {
> +			ret = -ENOMEM;
> +			goto bad;
> +		}
> +
> +		ret = stack_filter_copy(new_filter, filter);
> +		if (ret < 0)
> +			goto bad;
> +
> +		list_add(&new_filter->list, copy);
> +	}
> +	return 0;
> +
> + bad:
> +	stack_filter_list_clear(copy);
> +	return ret;
> +}
> +
> +static inline void
> +stack_filter_enable(struct trace_event_file *file)
> +{
> +	unsigned long old_flags = file->flags;
> +
> +	file->flags |= EVENT_FILE_FL_STACK_FILTER;
> +	if (file->flags != old_flags)
> +		trace_buffered_event_enable();
> +}
> +
> +static inline void
> +stack_filter_disable(struct trace_event_file *file)
> +{
> +	unsigned long old_flags = file->flags;
> +
> +	file->flags &= ~EVENT_FILE_FL_STACK_FILTER;
> +	if (file->flags != old_flags)
> +		trace_buffered_event_disable();
> +}
> +
> +static inline void
> +addr_map_init(struct stack_filter_addr_map *addr_map)

Same thing for this init function.

> +{
> +	int i;
> +
> +	for (i = 0; i < STACK_FILTER_ADDR_MAP_SIZE; i++)
> +		INIT_HLIST_HEAD(&addr_map->map[i]);
> +	spin_lock_init(&addr_map->lock);
> +}
> +
> +/*
> + * Typically, the number of functions in the call stack of a trace event
> + * is not large, so we use a simple hash table to store the mapping,
> + * without limiting its cache size.
> + */
> +static inline int
> +addr_map_insert(struct stack_filter_addr_map *addr_map, unsigned long key, unsigned long value)
> +{
> +	struct addr_map_node *node;
> +	int idx, ret = 0;
> +	unsigned long flags;
> +
> +	idx = ADDR_MAP_HASH(key);
> +	spin_lock_irqsave(&addr_map->lock, flags);
> +
> +	hlist_for_each_entry(node, &addr_map->map[idx], node) {
> +		/* new value is always the same as the old here... maybe */
> +		if (node->key == key)
> +			goto out;
> +	}
> +
> +	node = kmalloc(sizeof(*node), GFP_ATOMIC);
> +	if (!node) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	node->key = key;
> +	node->value = value;
> +
> +	hlist_add_head_rcu(&node->node, &addr_map->map[idx]);
> +
> + out:
> +	spin_unlock_irqrestore(&addr_map->lock, flags);
> +	return ret;
> +}
> +
> +static inline unsigned long
> +addr_map_get(struct stack_filter_addr_map *addr_map, unsigned long key)
> +{
> +	struct addr_map_node *node;
> +	int idx;
> +	unsigned long ret = 0; /* value can't be 0 */
> +
> +	idx = ADDR_MAP_HASH(key);
> +	/* nested critical section, not necessary in fact */
> +	rcu_read_lock_sched();
> +
> +	hlist_for_each_entry_rcu(node, &addr_map->map[idx], node) {
> +		if (node->key == key) {
> +			ret = node->value;
> +			goto out;
> +		}
> +	}
> +
> + out:
> +	rcu_read_unlock_sched();
> +	return ret;
> +}
> +
> +/* Require holding event_mutex */
> +static inline void
> +addr_map_clear(struct hlist_head *addr_map)
> +{
> +	int i;
> +	struct addr_map_node *node;
> +	struct hlist_node *tmp;
> +
> +	for (i = 0; i < STACK_FILTER_ADDR_MAP_SIZE; i++) {
> +		hlist_for_each_entry_safe(node, tmp, &addr_map[i], node) {
> +			hlist_del(&node->node);
> +			kfree(node);
> +		}
> +	}
> +}
> +
> +static inline void
> +addr_map_free(struct stack_filter_addr_map *addr_map)
> +{
> +	addr_map_clear(addr_map->map);
> +	kfree(addr_map);
> +}
> +
> +static inline void
> +event_stack_filter_init(struct event_stack_filter *esf)
> +{
> +	INIT_LIST_HEAD(&esf->filters);
> +
> +	/* addr_map should be pre-allocated, just init it here */
> +	addr_map_init(esf->addr_map);
> +}
> +
> +static inline struct event_stack_filter *
> +event_stack_filter_new(void)
> +{
> +	struct event_stack_filter *esf;
> +
> +	esf = kmalloc(sizeof(*esf), GFP_KERNEL);
> +	if (!esf)
> +		return NULL;
> +
> +	esf->addr_map = kmalloc(sizeof(*esf->addr_map), GFP_KERNEL);
> +	if (!esf->addr_map)
> +		return NULL;
> +
> +	event_stack_filter_init(esf);
> +	return esf;
> +}
> +
> +static inline void
> +event_stack_filter_free(struct event_stack_filter *esf, bool free_addr_map)
> +{
> +	stack_filter_list_clear(&esf->filters);
> +
> +	/*
> +	 * addr_map may be passed to a new event_stack_filter,
> +	 * in this situation, we cannot free it.
> +	 */
> +	if (free_addr_map)
> +		addr_map_free(esf->addr_map);
> +
> +	kfree(esf);
> +}
> +
> +/* Require holding event_mutex */
> +static inline int
> +event_stack_filter_copy(struct event_stack_filter *copy,
> +			struct event_stack_filter *esf)
> +{
> +	int ret;
> +
> +	ret = stack_filter_list_copy(&copy->filters, &esf->filters);
> +	if (ret < 0)
> +		return ret;
> +
> +	/*
> +	 * Not use deepcopy here to speed up copy.
> +	 * Must be vigilant about this when use or free addr_map.
> +	 */
> +	copy->addr_map = esf->addr_map;
> +	return 0;
> +}
> +
> +/*
> + * Allocate a new event_stack_filter and copy the old one.
> + * Require holding event_mutex.
> + */
> +static inline struct event_stack_filter *
> +event_stack_filter_clone(struct event_stack_filter *esf)
> +{
> +	struct event_stack_filter *copy;
> +
> +	copy = kmalloc(sizeof(*copy), GFP_KERNEL);
> +	if (!copy)
> +		return NULL;
> +
> +	if (event_stack_filter_copy(copy, esf) < 0) {
> +		kfree(copy);
> +		return NULL;
> +	}
> +
> +	return copy;
> +}
> +
> +/*
> + * Parse a string with the form below:
> + *   '!'?((function|'**')'/')*(function|'**')
> + * where:
> + *   '!' negates the filter
> + *   '**' matches any function call path
> + * e.g.
> + *   [1] work_pending/do_notify_resume/schedule/__schedule
> + *   [2] '**'/kthread/kcompactd/schedule_timeout/schedule/'**'
> + *   [3] !el0_sync/el0_sync_handler/'**'/invoke_syscall/'**'/schedule
> + *   [4] !ret_from_fork/'**'/kthread/worker_thread/schedule
> + *
> + * The full call path will end at stack_filter_match function,
> + * like "work_pending/do_notify_resume/schedule/__schedule/\
> + *   trace_event_raw_event_sched_switch/trace_event_buffer_commit/stack_filter_match".
> + *
> + * Call paths that matches example [1] can also match
> + *   schedule/__schedule/'**' or '**'/schedule/__schedule/'**'.
> + *
> + * We convert symbols to their addresses here to avoid
> + * changing stacktrace addresses to their names at runtime,
> + * which would greatly slow down the function call.
> + * The downside is that we can't handle '*' wildcard.

Yes you can ;-) You just need to record all the addresses that match the
wildcard. That is, faddr should have a list of addrs to match.

> + */
> +static int
> +stack_filter_parse(struct stack_filter *filter, char *buf)
> +{
> +	char *p = buf;
> +	char name[KSYM_NAME_LEN];
> +	struct function_address *faddr, *tmp;
> +	size_t addr;
> +	int i, len = 0, ret = 0;
> +
> +	if (*p == '!') {
> +		filter->neg = true;
> +		p++;
> +	}
> +	if (*p == '\0')
> +		return -EINVAL;
> +
> +	while (*p) {
> +		i = 0;
> +		while (*p && *p != '/') {
> +			name[i++] = *(p++);
> +			if (i > NAME_MAX) {
> +				ret = -EINVAL;
> +				goto bad;
> +			}
> +		}
> +		name[i] = '\0';
> +
> +		while (*p == '/')
> +			p++;
> +
> +		if (!strcmp(name, "**")) {
> +			/* wildcard '**' */
> +			addr = DSTARS_ADDR;
> +		} else {
> +			/* function name (maybe empty) */
> +			addr = kallsyms_lookup_name(name);
> +			if (!addr) {
> +				ret = -EINVAL;
> +				goto bad;
> +			}


Not only could faddr be a list, you want to save the start and end of the
function, as stack traces seldom (never) at the start. Did this actually
work for you?

		 kallsyms_lookup(addr, &symsize, NULL, NULL, NULL);

		faddr->addr_start = addr;
		faddr->addr_end = addr + symsize;

> +		}
> +
> +		/* remove repetitive '**' */
> +		if (addr == DSTARS_ADDR && !list_empty(&filter->addrs)) {
> +			faddr = list_first_entry(&filter->addrs, struct function_address, list);
> +
> +			if (faddr->addr == DSTARS_ADDR)
> +				continue;
> +		}
> +
> +		if (++len > MAX_SF_LEN) {
> +			ret = -EINVAL;
> +			goto bad;
> +		}
> +
> +		faddr = kzalloc(sizeof(*faddr), GFP_KERNEL);
> +		if (!faddr) {
> +			ret = -ENOMEM;
> +			goto bad;
> +		}
> +
> +		faddr->addr = addr;
> +		list_add(&faddr->list, &filter->addrs);
> +	}
> +
> +	if (list_empty(&filter->addrs))
> +		return -EINVAL;
> +
> +	if (list_first_entry(&filter->addrs, struct function_address, list)->addr != DSTARS_ADDR) {
> +		/* add '**' at the end */
> +		faddr = kzalloc(sizeof(*faddr), GFP_KERNEL);
> +		if (!faddr) {
> +			ret = -ENOMEM;
> +			goto bad;
> +		}
> +		faddr->addr = DSTARS_ADDR;
> +		list_add(&faddr->list, &filter->addrs);
> +	}
> +
> +	/* save original string as well */
> +	filter->string = kstrdup(buf, GFP_KERNEL);
> +	if (!filter->string) {
> +		ret = -ENOMEM;
> +		goto bad;
> +	}
> +
> +	return ret;
> +
> + bad:
> +	list_for_each_entry_safe(faddr, tmp, &filter->addrs, list) {
> +		list_del(&faddr->list);
> +		kfree(faddr);
> +	}
> +	return ret;
> +}
> +
> +/*
> + * Match the call stack with one stack filter.
> + */
> +static bool
> +__stack_filter_match_one(struct stack_filter *filter,
> +			 unsigned long *buf, int num_entries, bool *dp)
> +{
> +	int num_faddrs, i, j;
> +	bool ok;
> +	struct function_address *faddr;
> +
> +	num_faddrs = list_length(&filter->addrs);
> +
> +#define pos(i, j) ((i) * (num_faddrs + 1) + (j))
> +
> +	/* dynamic programming */
> +	dp[pos(0, 0)] = true;
> +	ok = false;
> +
> +	for (i = 0; i <= num_entries; i++) {
> +		faddr = list_entry(&filter->addrs, struct function_address, list);
> +		for (j = 1; j <= num_faddrs; j++) {
> +			faddr = list_next_entry(faddr, list);
> +			dp[pos(i, j)] = false;
> +
> +			if (faddr->addr == DSTARS_ADDR) {
> +				dp[pos(i, j)] = dp[pos(i, j - 1)];
> +				if (i > 0)
> +					dp[pos(i, j)] |= dp[pos(i - 1, j)];
> +			} else if (i > 0 && buf[i - 1] == faddr->addr)

Here we would match: buf[i - 1] >= faddr->addr_start && buf[i - 1] < faddr->addr_end

All in all, this does look promising.

I'm wondering if we should just make it part of the filter logic and not
use a separate file:

 echo 'stacktrace == "**/schedule_preempt_disable/**"' > events/sched/sched_switch/filter

And then we could even use it with triggers!

 echo 'stacktrace if stacktrace == "**/schedule_preempt_disable/**"' > events/sched/sched_switch/trigger

Thanks!

-- Steve


> +				dp[pos(i, j)] = dp[pos(i - 1, j - 1)];
> +		}
> +
> +		if (dp[pos(i, num_faddrs)]) {
> +			ok = true;
> +			break;
> +		}
> +	}
> +
> +#undef pos
> +
> +	return ok;
> +}
> +
> +/*
> + * Convert function_address + offset to function_address.
> + * Return 0 on error.
> + */
> +static inline unsigned long
> +addr_remove_offset(struct event_stack_filter *esf, unsigned long addr)
> +{
> +	unsigned long new_addr;
> +	char name[KSYM_NAME_LEN];
> +
> +	/*
> +	 * This operation is very slow,
> +	 * so we use a small cache to optimize it.
> +	 */
> +	new_addr = addr_map_get(esf->addr_map, addr);
> +	if (new_addr)
> +		return new_addr;
> +
> +	if (lookup_symbol_name(addr, name) < 0)
> +		return 0;
> +
> +	new_addr = kallsyms_lookup_name(name);
> +	if (!new_addr)
> +		return 0;
> +
> +	if (addr_map_insert(esf->addr_map, addr, new_addr) < 0)
> +		return 0;
> +
> +	return new_addr;
> +}
> +
> +/*
> + * return 1 on matching and 0 otherwise.
> + *
> + * A call path is matched successfully if the following conditions are met simultaneously:
> + * [1] It matches any positive stack filter.
> + * [2] It doesn't match any negative stack filter.
> + * If no positive filter are set, condition [1] don't need to be satisified.
> + */
> +int stack_filter_match(struct event_stack_filter *esf)
> +{
> +	int i, num_entries, num_faddrs;
> +	int size, maxsize;
> +	bool hasp, okp, *dp;
> +	struct stack_filter *filter;
> +	unsigned long *buf, new_addr;
> +	struct list_head *stack_filters;
> +
> +	/*
> +	 * We have already been inside rcu_read_lock_sched critical section.
> +	 * It's safe to visit esf.
> +	 */
> +	if (!esf)
> +		return 1;
> +
> +	stack_filters = &esf->filters;
> +	if (list_empty(stack_filters))
> +		return 1;
> +
> +	buf = kmalloc_array(STACK_BUF_SIZE, sizeof(*buf), GFP_ATOMIC);
> +	if (!buf)
> +		return 0;
> +
> +	num_entries = stack_trace_save(buf, STACK_BUF_SIZE, 0);
> +
> +	for (i = num_entries - 1; i >= 0; i--) {
> +		/*
> +		 * buf[i] contains addr of a symbol plus an offset.
> +		 * We should remove the offset here.
> +		 */
> +		new_addr = addr_remove_offset(esf, buf[i]);
> +		if (new_addr)
> +			buf[i] = new_addr;
> +	}
> +
> +	/* pre allocate memory for dp */
> +	maxsize = 0;
> +	list_for_each_entry(filter, stack_filters, list) {
> +		num_faddrs = list_length(&filter->addrs);
> +		size = (num_entries + 1) * (num_faddrs + 1);
> +
> +		if (size > maxsize)
> +			maxsize = size;
> +	}
> +
> +	dp = kmalloc(maxsize, GFP_ATOMIC);
> +	if (!dp) {
> +		kfree(buf);
> +		return 0;
> +	}
> +
> +	hasp = 0; okp = 0;
> +	list_for_each_entry(filter, stack_filters, list) {
> +		if (!filter->neg) {
> +			hasp = 1;
> +			if (__stack_filter_match_one(filter, buf, num_entries, dp)) {
> +				okp = 1;
> +				break;
> +			}
> +		}
> +	}
> +	if (hasp && !okp)
> +		goto bad_match;
> +
> +	list_for_each_entry(filter, stack_filters, list) {
> +		if (filter->neg && __stack_filter_match_one(filter, buf, num_entries, dp))
> +			goto bad_match;
> +	}
> +
> +	kfree(dp);
> +	kfree(buf);
> +	return 1;
> +
> + bad_match:
> +	kfree(dp);
> +	kfree(buf);
> +	return 0;
> +}
> +
> +/*
> + * Use seq_file APIs to read from stack_filters
> + */
> +static void *sf_start(struct seq_file *m, loff_t *pos)
> +{
> +	struct trace_event_file *file;
> +	loff_t n = *pos;
> +
> +	mutex_lock(&event_mutex);
> +	file = m->private;
> +
> +	if (!file->stack_filter)
> +		return NULL;
> +
> +	return seq_list_start(&file->stack_filter->filters, n);
> +}
> +
> +static void *sf_next(struct seq_file *m, void *v, loff_t *pos)
> +{
> +	struct trace_event_file *file = m->private;
> +
> +	return seq_list_next(v, &file->stack_filter->filters, pos);
> +}
> +
> +static void sf_stop(struct seq_file *m, void *v)
> +{
> +	mutex_unlock(&event_mutex);
> +}
> +
> +static int sf_show(struct seq_file *m, void *v)
> +{
> +	struct stack_filter *filter = v;
> +
> +	seq_printf(m, "%s\n", filter->string);
> +	return 0;
> +}
> +
> +const struct seq_operations stack_filter_seq_ops = {
> +	.start = sf_start,
> +	.stop = sf_stop,
> +	.next = sf_next,
> +	.show = sf_show,
> +};
> +
> +static ssize_t
> +event_stack_filter_write(struct file *filp, const char __user *ubuf,
> +			 size_t cnt, loff_t *ppos)
> +{
> +	struct trace_event_file *event_file;
> +	struct trace_parser parser;
> +	struct stack_filter *filter;
> +	struct event_stack_filter *esf, *old;
> +	int read, ret;
> +
> +	filter = stack_filter_new();
> +	if (!filter)
> +		return -ENOMEM;
> +
> +	if (trace_parser_get_init(&parser, PARSER_BUF_SIZE + 1)) {
> +		kfree(filter);
> +		return -ENOMEM;
> +	}
> +
> +	read = trace_get_user(&parser, ubuf, cnt, ppos);
> +
> +	if (read >= 0 && trace_parser_loaded(&parser)) {
> +		/*
> +		 * e.g. use 'echo 0 > stack_filter' to disable stack_filter
> +		 * Most data structures has been cleared in event_stack_filter_open.
> +		 * Just make some judgements to avoid reporting error.
> +		 */
> +		if (!strcmp(strstrip(parser.buffer), "0")) {
> +			kfree(filter);
> +			trace_parser_put(&parser);
> +
> +			event_file = event_file_data(filp);
> +			if (!rcu_dereference(event_file->stack_filter))
> +				return read;
> +
> +			/* maybe use append mode or something else */
> +			return -EINVAL;
> +		}
> +
> +		ret = stack_filter_parse(filter, parser.buffer);
> +		if (ret < 0) {
> +			kfree(filter);
> +			trace_parser_put(&parser);
> +			return ret;
> +		}
> +	} else {
> +		kfree(filter);
> +		goto out;
> +	}
> +
> +	mutex_lock(&event_mutex);
> +	event_file = event_file_data(filp);
> +
> +	if (event_file->stack_filter) {
> +		/*
> +		 * Copy the old and replace it with the new one to follow rcu rules.
> +		 * It doesn't cost much time since this function is called seldomly.
> +		 * In this way, codes can be simple.
> +		 *
> +		 * We didn't use a separate rcu for stack_filter->filters
> +		 * since its elements cannot be deleted one by one.
> +		 */
> +		esf = event_stack_filter_clone(event_file->stack_filter);
> +		if (!esf) {
> +			mutex_unlock(&event_mutex);
> +			stack_filter_free(filter);
> +			goto out;
> +		}
> +		list_add_tail(&filter->list, &esf->filters);
> +
> +		old = event_file->stack_filter;
> +		rcu_assign_pointer(event_file->stack_filter, esf);
> +
> +		/* make sure old esf is not being used */
> +		tracepoint_synchronize_unregister();
> +		event_stack_filter_free(old, false);
> +
> +	} else {
> +		esf = event_stack_filter_new();
> +		if (!esf) {
> +			mutex_unlock(&event_mutex);
> +			stack_filter_free(filter);
> +			goto out;
> +		}
> +		list_add_tail(&filter->list, &esf->filters);
> +
> +		rcu_assign_pointer(event_file->stack_filter, esf);
> +		tracepoint_synchronize_unregister();
> +
> +		stack_filter_enable(event_file);
> +	}
> +
> +	mutex_unlock(&event_mutex);
> +
> + out:
> +	trace_parser_put(&parser);
> +	return read;
> +}
> +
> +static int event_stack_filter_open(struct inode *inode, struct file *filp)
> +{
> +	int ret;
> +	struct trace_event_file *event_file;
> +	struct event_stack_filter *esf;
> +	struct seq_file *seq;
> +
> +	ret = security_locked_down(LOCKDOWN_TRACEFS);
> +	if (ret)
> +		return ret;
> +
> +	mutex_lock(&event_mutex);
> +
> +	event_file = inode->i_private;
> +	if (!event_file) {
> +		mutex_unlock(&event_mutex);
> +		return -ENODEV;
> +	}
> +
> +	if ((filp->f_mode & FMODE_WRITE) && (filp->f_flags & O_TRUNC)) {
> +		stack_filter_disable(event_file);
> +
> +		if (event_file->stack_filter) {
> +			esf = event_file->stack_filter;
> +			RCU_INIT_POINTER(event_file->stack_filter, NULL);
> +
> +			/* wait until esf is not being used */
> +			tracepoint_synchronize_unregister();
> +			event_stack_filter_free(esf, true);
> +		}
> +	}
> +
> +	ret = seq_open(filp, &stack_filter_seq_ops);
> +	if (!ret) {
> +		seq = filp->private_data;
> +		seq->private = inode->i_private;
> +	}
> +
> +	mutex_unlock(&event_mutex);
> +
> +	return ret;
> +}
> +
> +/*
> + * Operations for file "stack_filter"
> + */
> +const struct file_operations event_stack_filter_fops = {
> +	.open = event_stack_filter_open,
> +	.read = seq_read,
> +	.write = event_stack_filter_write,
> +	.llseek = tracing_lseek,
> +	.release = seq_release,
> +};

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