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SubjectRe: [PATCH] trace: Add trace any kernel object
On Thu, Oct 14, 2021 at 10:21 AM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> [ Added Masami ]
>
> On Thu, 14 Oct 2021 09:44:45 +0800
> Jeff Xie <xiehuan09@gmail.com> wrote:
>
> > Introduce a method based on function tracer and kprobe event
> > to trace any object in the linux kernel.
>
> I first want to say that this looks really interesting, and something
> that can help out a lot!

I'm very glad you like this idea.

>
> That said, we are going to have to work with you to come up with a
> better and more flexible interface, and make sure locking and
> synchronization works.

Thank you very much for your help .I am not currently a full-time
Linux kernel developer, and hope to work hard to submit
more quality kernel patches.I view the kernel code almost every day.
However, few patches have been submitted so far:).
I have viewed the ftrace source code for about half a year and am very
interested in and watched all the videos about ftrace
you published on the internet.

>
> >
> > Usage:
> > When using the kprobe event, only need to enable trace_object,
> > we can trace any function argument or the return value. When
> > the object passes through a function, it can be traced.
> >
> > For example:
> >
> > For the function bio_add_page, we can trace the first argument:
> >
> > int bio_add_page(struct bio *bio, struct page *page,
> > unsigned int len, unsigned int offset)
> >
> > #cd /sys/kernel/debug/tracing
> > #echo 1 > ./trace_object
> > #echo 'p bio_add_page arg1=$arg1' > kprobe_events
> > #echo 1 > ./events/kprobes/p_bio_add_page_0/enable
> > #sync
> > #cat ./trace
> >
> > # tracer: nop
> > #
> > # entries-in-buffer/entries-written: 367/367 #P:4
> > #
> > # _-----=> irqs-off
> > # / _----=> need-resched
> > # | / _---=> hardirq/softirq
> > # || / _--=> preempt-depth
> > # ||| / _-=> migrate-disable
> > # |||| / delay
> > # TASK-PID CPU# ||||| TIMESTAMP FUNCTION
> > # | | | ||||| | |
> > kworker/u8:5-89 [000] ..... 60.310385: p_bio_add_page_0: (bio_add_page+0x0/0x90) arg1=0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310386: bio_add_page <-ext4_bio_write_page object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310387: __bio_try_merge_page <-bio_add_page object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310387: __bio_add_page <-bio_add_page object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310389: submit_bio <-ext4_io_submit object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310389: submit_bio <-ext4_io_submit object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310389: submit_bio_noacct <-ext4_io_submit object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310389: submit_bio_checks <-submit_bio_noacct object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310390: __cond_resched <-submit_bio_checks object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310390: rcu_all_qs <-__cond_resched object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310390: should_fail_bio <-submit_bio_checks object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310391: blk_mq_submit_bio <-submit_bio_noacct object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310392: blk_attempt_plug_merge <-blk_mq_submit_bio object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310392: __blk_mq_sched_bio_merge <-blk_mq_submit_bio object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310392: __blk_mq_alloc_request <-blk_mq_submit_bio object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310393: blk_mq_get_tag <-__blk_mq_alloc_request object:0xffff888102bde780
> > kworker/u8:5-89 [000] ..... 60.310394: blk_account_io_start <-blk_mq_submit_bio object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311264: bio_advance <-blk_update_request object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311265: bio_endio <-blk_update_request object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311265: ext4_end_bio <-blk_update_request object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311266: ext4_finish_bio <-ext4_end_bio object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311274: bio_put <-ext4_end_bio object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311274: bio_free <-ext4_end_bio object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311274: bio_free <-ext4_end_bio object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311274: bvec_free <-bio_free object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311275: mempool_free <-bio_free object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311275: mempool_free_slab <-bio_free object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311275: mempool_free <-ext4_end_bio object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311275: mempool_free_slab <-ext4_end_bio object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311275: kmem_cache_free <-ext4_end_bio object:0xffff888102bde780
> > <idle>-0 [000] d.... 60.311276: kmem_cache_free <-ext4_end_bio object:0xffff888102bde780
> > ...
> >
>
> So if I understand the above, if you set this "trace_object" then
> whatever gets placed into a kprobe parameter ($arg1?) or a return value
> of a kretprobe, gets traced at every other function call?

Yes, your understanding is correct

>
>
> > Signed-off-by: Jeff Xie <xiehuan09@gmail.com>
> > ---
> > include/linux/ftrace.h | 6 ++
> > kernel/trace/Kconfig | 7 ++
> > kernel/trace/Makefile | 1 +
> > kernel/trace/trace.c | 69 +++++++++++++++++++
> > kernel/trace/trace.h | 2 +
> > kernel/trace/trace_entries.h | 17 +++++
> > kernel/trace/trace_kprobe.c | 6 ++
> > kernel/trace/trace_object.c | 128 +++++++++++++++++++++++++++++++++++
> > kernel/trace/trace_output.c | 40 +++++++++++
> > 9 files changed, 276 insertions(+)
> > create mode 100644 kernel/trace/trace_object.c
> >
> > diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
> > index 832e65f06754..2e097a5fa462 100644
> > --- a/include/linux/ftrace.h
> > +++ b/include/linux/ftrace.h
> > @@ -1078,4 +1078,10 @@ unsigned long arch_syscall_addr(int nr);
> >
> > #endif /* CONFIG_FTRACE_SYSCALLS */
> >
> > +#ifdef CONFIG_TRACE_OBJECT
> > +int init_trace_object(void);
> > +int exit_trace_object(void);
> > +void set_trace_object(void *obj);
>
> Add here:
>
> #else
> static inline int init_trace_object(void) { return 0; }
> static inline int exit_trace_object(void) { return 0; }
> static inline void set_trace_object(void *obj) { }
>
> > +#endif
>
> This will allow you to get rid of the ugly "#ifdef"s all over the code
> below.
>
> > +
> > #endif /* _LINUX_FTRACE_H */
> > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> > index 420ff4bc67fd..d302a0f085f9 100644
> > --- a/kernel/trace/Kconfig
> > +++ b/kernel/trace/Kconfig
> > @@ -237,6 +237,13 @@ config FUNCTION_PROFILER
> >
> > If in doubt, say N.
> >
> > +config TRACE_OBJECT
> > + bool "Trace kernel object"
> > + depends on FUNCTION_TRACER
> > + default y
> > + help
> > + This help kernel developer to trace any kernel object.
>
> We'll need to work with you to come up with a better description.
>
> > +
> > config STACK_TRACER
> > bool "Trace max stack"
> > depends on HAVE_FUNCTION_TRACER
> > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
> > index 6de5d4d63165..6d9e78a488aa 100644
> > --- a/kernel/trace/Makefile
> > +++ b/kernel/trace/Makefile
> > @@ -66,6 +66,7 @@ obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += trace_functions_graph.o
> > obj-$(CONFIG_TRACE_BRANCH_PROFILING) += trace_branch.o
> > obj-$(CONFIG_BLK_DEV_IO_TRACE) += blktrace.o
> > obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += fgraph.o
> > +obj-$(CONFIG_TRACE_OBJECT) += trace_object.o
> > ifeq ($(CONFIG_BLOCK),y)
> > obj-$(CONFIG_EVENT_TRACING) += blktrace.o
> > endif
> > diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> > index 7896d30d90f7..8069562bfde1 100644
> > --- a/kernel/trace/trace.c
> > +++ b/kernel/trace/trace.c
> > @@ -9412,6 +9412,70 @@ static __init void create_trace_instances(struct dentry *d_tracer)
> > mutex_unlock(&event_mutex);
> > }
> >
> > +#if defined(CONFIG_TRACE_OBJECT)
> > +
> > +static DEFINE_MUTEX(trace_object_lock);
>
> You don't want a mutex here. And if possible, we should try to
> synchronize this with RCU. But if that can't happen, we need this to be
> a raw_spin_lock().
>
> > +static int trace_object_enabled __read_mostly;
> > +
> > +static ssize_t
> > +trace_object_read(struct file *filp, char __user *ubuf,
> > + size_t cnt, loff_t *ppos)
> > +{
> > + char buf[64];
> > + int r;
> > +
> > + r = sprintf(buf, "%u\n", trace_object_enabled);
> > + return simple_read_from_buffer(ubuf, cnt, ppos, buf, r);
> > +}
> > +
> > +static ssize_t
> > +trace_object_write(struct file *filp, const char __user *ubuf,
> > + size_t cnt, loff_t *ppos)
> > +{
> > + unsigned long val;
> > + int ret;
> > +
> > + ret = kstrtoul_from_user(ubuf, cnt, 10, &val);
> > + if (ret)
> > + return ret;
> > +
> > + val = !!val;
> > +
> > + mutex_lock(&trace_object_lock);
> > + if (trace_object_enabled ^ val) {
> > + if (val) {
> > + ret = init_trace_object();
> > + if (ret < 0) {
> > + cnt = ret;
> > + goto out;
> > + }
> > +
> > + trace_object_enabled = 1;
> > + } else {
> > + ret = exit_trace_object();
> > + if (ret < 0) {
> > + cnt = ret;
> > + goto out;
> > + }
> > +
> > + trace_object_enabled = 0;
> > + }
> > + }
> > +out:
> > + mutex_unlock(&trace_object_lock);
> > + *ppos += cnt;
> > + return cnt;
> > +}
> > +
> > +static const struct file_operations trace_object_fops = {
> > + .open = tracing_open_generic,
> > + .read = trace_object_read,
> > + .write = trace_object_write,
> > + .llseek = default_llseek,
>
> Honestly, I don't think this should be implemented by a file. What
> could work, and Masami let me know your thoughts, is to add something
> to the kprobe/uprobe/eprobe interface. That is:
>
> # echo 'p bio_add_page arg1=$arg1:trace' > kprobe_events

Great, this one looks more advanced.

# echo 'p bio_add_page arg1=$arg1:trace' > kprobe_events
>
> Or something, that we explicitly set on the kprobe itself, and then we
> can pick what we want to trace, especially if we only want to trace
> one item in the list.

If we only want to trace one function or pick what we want to trace, we can
set the file set_ftrace_filter in my understanding.

>
> > +};
> > +
> > +#endif
> > +
> > static void
> > init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
> > {
> > @@ -9477,6 +9541,11 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
> > trace_create_maxlat_file(tr, d_tracer);
> > #endif
> >
> > +#if defined(CONFIG_TRACE_OBJECT)
> > + trace_create_file("trace_object", 0644, d_tracer, tr,
> > + &trace_object_fops);
> > +#endif
> > +
> > if (ftrace_create_function_files(tr, d_tracer))
> > MEM_FAIL(1, "Could not allocate function filter files");
> >
> > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> > index b7c0f8e160fb..bf6bcaa24e1a 100644
> > --- a/kernel/trace/trace.h
> > +++ b/kernel/trace/trace.h
> > @@ -49,6 +49,7 @@ enum trace_type {
> > TRACE_TIMERLAT,
> > TRACE_RAW_DATA,
> > TRACE_FUNC_REPEATS,
> > + TRACE_OBJECT,
> >
> > __TRACE_LAST_TYPE,
> > };
> > @@ -460,6 +461,7 @@ extern void __ftrace_bad_type(void);
> > TRACE_GRAPH_RET); \
> > IF_ASSIGN(var, ent, struct func_repeats_entry, \
> > TRACE_FUNC_REPEATS); \
> > + IF_ASSIGN(var, ent, struct trace_object_entry, TRACE_OBJECT);\
> > __ftrace_bad_type(); \
> > } while (0)
> >
> > diff --git a/kernel/trace/trace_entries.h b/kernel/trace/trace_entries.h
> > index cd41e863b51c..27bababc0ed4 100644
> > --- a/kernel/trace/trace_entries.h
> > +++ b/kernel/trace/trace_entries.h
> > @@ -401,3 +401,20 @@ FTRACE_ENTRY(timerlat, timerlat_entry,
> > __entry->context,
> > __entry->timer_latency)
> > );
> > +
> > +/*
> > + * trace object entry:
> > + */
> > +FTRACE_ENTRY(object, trace_object_entry,
> > +
> > + TRACE_OBJECT,
> > +
> > + F_STRUCT(
> > + __field( unsigned long, ip )
> > + __field( unsigned long, parent_ip )
> > + __field( unsigned long, object )
> > + ),
> > +
> > + F_printk(" %ps <-- %ps object:%lx\n",
> > + (void *)__entry->ip, (void *)__entry->parent_ip, __entry->object)
> > +);
> > diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> > index 3a64ba4bbad6..0d46670702d9 100644
> > --- a/kernel/trace/trace_kprobe.c
> > +++ b/kernel/trace/trace_kprobe.c
> > @@ -1341,6 +1341,9 @@ process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
> > break;
> > case FETCH_OP_RETVAL:
> > val = regs_return_value(regs);
> > +#ifdef CONFIG_TRACE_OBJECT
> > + set_trace_object((void *)val);
>
> This can be called from atomic context.
> > +#endif
> > break;
> > case FETCH_OP_IMM:
> > val = code->immediate;
> > @@ -1354,6 +1357,9 @@ process_fetch_insn(struct fetch_insn *code, void *rec, void *dest,
> > #ifdef CONFIG_HAVE_FUNCTION_ARG_ACCESS_API
> > case FETCH_OP_ARG:
> > val = regs_get_kernel_argument(regs, code->param);
> > +#ifdef CONFIG_TRACE_OBJECT
> > + set_trace_object((void *)val);
> > +#endif
> > break;
> > #endif
> > case FETCH_NOP_SYMBOL: /* Ignore a place holder */
> > diff --git a/kernel/trace/trace_object.c b/kernel/trace/trace_object.c
> > new file mode 100644
> > index 000000000000..eb8edfebecee
> > --- /dev/null
> > +++ b/kernel/trace/trace_object.c
> > @@ -0,0 +1,126 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * trace any object
> > + * Copyright (C) 2021 Jeff Xie <xiehuan09@gmail.com>
> > + */
> > +
> > +#define pr_fmt(fmt) "trace_object: " fmt
> > +
> > +#include "trace_output.h"
> > +
> > +static DEFINE_PER_CPU(atomic_t, trace_object_event_disable);
> > +static DEFINE_MUTEX(object_mutex_lock);
> > +static struct trace_event_file event_trace_file;
> > +
> > +#define MAX_TRACE_OBJ_NUM 1024
> > +static unsigned long *global_trace_obj;
> > +static int global_trace_count;
> > +static const int max_args_num = 6;
> > +
> > +void set_trace_object(void *obj)
> > +{
> > + int i;
> > +
> > + if (!obj || global_trace_count == MAX_TRACE_OBJ_NUM)
> > + goto out;
> > +
> > + for (i = 0; i < global_trace_count; i++) {
> > + if (global_trace_obj[i] == (unsigned long)obj)
> > + goto out;
> > + }
> > + mutex_lock(&object_mutex_lock);
> As stated above, this can be called from atomic context, and you can't
> have a mutex here.

I'm so sorry, I ignored it.

>
> > +
> > + global_trace_obj[global_trace_count++] = (unsigned long)obj;
> > +
> > + mutex_unlock(&object_mutex_lock);
> > +out:
> > + return;
> > +}
> > +
> > +static void submit_trace_object(unsigned long ip, unsigned long
> > parent_ip,
> > + unsigned long object)
> > +{
> > +
> > + struct trace_buffer *buffer;
> > + struct ring_buffer_event *event;
> > + struct trace_object_entry *entry;
> > + int pc;
> > +
> > + pc = preempt_count();
> > + event = trace_event_buffer_lock_reserve(&buffer,
> > &event_trace_file,
> > + TRACE_OBJECT, sizeof(*entry), pc);
> > + if (!event)
> > + return;
> > + entry = ring_buffer_event_data(event);
> > + entry->ip = ip;
> > + entry->parent_ip = parent_ip;
> > + entry->object = object;
> > +
> > + event_trigger_unlock_commit(&event_trace_file, buffer, event,
> > + entry, pc);
> > +}
> > +
> > +static void
> > +trace_object_events_call(unsigned long ip, unsigned long parent_ip,
> > + struct ftrace_ops *op, struct ftrace_regs *fregs)
> > +{
> > + struct pt_regs *pt_regs = ftrace_get_regs(fregs);
> > + unsigned long object;
> > + long disabled;
> > + int cpu, n, i;
> > +
> > + preempt_disable_notrace();
> > +
> > + cpu = raw_smp_processor_id();
> > + disabled =
> > atomic_inc_return(&per_cpu(trace_object_event_disable, cpu)); +
> > + if (disabled != 1)
> > + goto out;
> > +
> > + if (!global_trace_obj[0])
> > + goto out;
> > +
> > + for (n = 0; n < max_args_num; n++) {
> > + object = regs_get_kernel_argument(pt_regs, n);
> > + for (i = 0; i < global_trace_count; i++) {
> > + if (object == global_trace_obj[i])
> > + submit_trace_object(ip, parent_ip,
> > object);
>
> I'm thinking we could possibly, make this a single event, with dynamic
> arrays.

okay, I also hope to implement a better way of handling in this place.

>
> > + }
> > + }
> > +out:
> > + atomic_dec(&per_cpu(trace_object_event_disable, cpu));
> > + preempt_enable_notrace();
> > +}
> > +
> > +static struct ftrace_ops trace_ops = {
> > + .func = trace_object_events_call,
> > + .flags = FTRACE_OPS_FL_SAVE_REGS,
> > +};
> > +
> > +int init_trace_object(void)
> > +{
> > + int ret;
> > +
> > + event_trace_file.tr = top_trace_array();
> > + if (WARN_ON(!event_trace_file.tr))
> > + return -1;
> > +
> > + global_trace_obj = kzalloc(sizeof(unsigned long) * MAX_TRACE_OBJ_NUM,
> > + GFP_KERNEL);
> > + if (!global_trace_obj)
> > + return -ENOMEM;
> > +
> > + ret = register_ftrace_function(&trace_ops);
> > +
> > + return ret;
> > +}
> > +
> > +int exit_trace_object(void)
> > +{
> > + int ret;
> > +
> > + ret = unregister_ftrace_function(&trace_ops);
> > +
> > + kfree(global_trace_obj);
> > + return ret;
> > +}
> > diff --git a/kernel/trace/trace_output.c b/kernel/trace/trace_output.c
> > index c2ca40e8595b..21a9c8737929 100644
> > --- a/kernel/trace/trace_output.c
> > +++ b/kernel/trace/trace_output.c
> > @@ -1552,6 +1552,45 @@ static struct trace_event trace_func_repeats_event = {
> > .funcs = &trace_func_repeats_funcs,
> > };
> >
> > +/* TRACE_OBJECT */
> > +static enum print_line_t trace_object_print(struct trace_iterator *iter, int flags,
> > + struct trace_event *event)
> > +{
> > + struct trace_object_entry *field;
> > + struct trace_seq *s = &iter->seq;
> > +
> > + trace_assign_type(field, iter->ent);
> > + print_fn_trace(s, field->ip, field->parent_ip, flags);
> > + trace_seq_printf(s, " object:0x%lx", field->object);
> > + trace_seq_putc(s, '\n');
> > +
> > + return trace_handle_return(s);
> > +}
> > +
> > +static enum print_line_t trace_object_raw(struct trace_iterator *iter, int flags,
> > + struct trace_event *event)
> > +{
> > + struct trace_object_entry *field;
> > +
> > + trace_assign_type(field, iter->ent);
> > +
> > + trace_seq_printf(&iter->seq, "%lx %lx\n",
> > + field->ip,
> > + field->parent_ip);
> > +
> > + return trace_handle_return(&iter->seq);
> > +}
> > +
> > +static struct trace_event_functions trace_object_funcs = {
> > + .trace = trace_object_print,
> > + .raw = trace_object_raw,
> > +};
> > +
> > +static struct trace_event trace_object_event = {
> > + .type = TRACE_OBJECT,
> > + .funcs = &trace_object_funcs,
> > +};
> > +
> > static struct trace_event *events[] __initdata = {
> > &trace_fn_event,
> > &trace_ctx_event,
> > @@ -1566,6 +1605,7 @@ static struct trace_event *events[] __initdata = {
> > &trace_timerlat_event,
> > &trace_raw_data_event,
> > &trace_func_repeats_event,
> > + &trace_object_event,
> > NULL
> > };
> >
>
> So in conclusion, I really like this idea. Now we need to help you
> clean it up, and make a proper interface and something that is flexible
> as well.
>
> Looking forward to working with you more on this.
>
> Cheers,
>
> -- Steve

It's my honor to get your help. Thank you for your detailed comments
and glad for your quick response.

---
JeffXie
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