Messages in this thread | | | From | Jeff Xie <> | Date | Tue, 21 Dec 2021 18:29:27 +0800 | Subject | Re: [RFC][PATCH v6 1/5] trace: Add trace any kernel object |
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Hi Masami,
On Tue, Dec 21, 2021 at 3:36 PM Masami Hiramatsu <mhiramat@kernel.org> wrote: > > Hi Jeff, > > On Sat, 18 Dec 2021 00:32:57 +0800 > Jeff Xie <xiehuan09@gmail.com> wrote: > > > > > +struct object_instance { > > > > + void *object; > > > > + struct freelist_node free_list; > > > > + struct list_head active_list; > > > > +}; > > > > + > > > > +struct obj_pool { > > > > + struct freelist_head free_list; > > > > + struct list_head active_list; > > > > +}; > > > > +static struct obj_pool *obj_pool; > > > > + > > > > +static bool object_exist(void *obj) > > > > +{ > > > > + struct object_instance *inst; > > > > + bool ret = false; > > > > + > > > > + list_for_each_entry_rcu(inst, &obj_pool->active_list, active_list) { > > > > + if (inst->object == obj) { > > > > + ret = true; > > > > + goto out; > > > > + } > > > > + } > > > > +out: > > > > + return ret; > > > > +} > > > > + > > > > +static bool object_empty(void) > > > > +{ > > > > + return list_empty(&obj_pool->active_list); > > > > +} > > > > + > > > > +static void set_trace_object(void *obj) > > > > +{ > > > > + struct freelist_node *fn; > > > > + struct object_instance *ins; > > > > + unsigned long flags; > > > > + > > > > + if (in_nmi()) > > > > + return; > > > > + > > > > + if (!obj) > > > > + return; > > > > + > > > > + if (object_exist(obj)) > > > > + return; > > > > + > > > > + fn = freelist_try_get(&obj_pool->free_list); > > > > + if (!fn) { > > > > + trace_printk("object_pool is full, can't trace object:0x%px\n", obj); > > > > + return; > > > > + } > > > > + > > > > + ins = container_of(fn, struct object_instance, free_list); > > > > + ins->object = obj; > > > > + > > > > + raw_spin_lock_irqsave(&object_spin_lock, flags); > > > > + list_add_rcu(&ins->active_list, &obj_pool->active_list); > > > > + raw_spin_unlock_irqrestore(&object_spin_lock, flags); > > > > > > Please add a comment that why this spinlock is needed here and why > > > other operation doesn't need it. > > > > (Only this place has write operations, and it cannot be concurrent) > > I agree, I will add it. > > BTW, I have another better solution for object pool. If the > object pool size is fixed (of course to avoid performance overhead, > it should be small enough) and it can not avoid using spinlock, > it is better to use fixed-size array. That makes the implementation > much simpler.
This looks really simpler, I will add it in the next version ;-)
> static struct object_instance { > void *obj; /* trace object */ > // add offset in the next patch > } traced_obj[MAX_TRACE_OBJECT]; > > static atomic_t num_traced_obj; > static DEFINE_RAW_SPINLOCK(trace_obj_lock); > > static void set_trace_object(void *obj) > { > ... > > raw_spin_lock_irqsave(&trace_obj_lock, flags); > if (num_traced_obj == MAX_TRACED_OBJECT) > goto out; > > traced_obj[num_traced_obj].obj = obj; > smp_wmb(); // make sure the num_traced_obj update always appears after trace_obj update. > num_traced_obj++;
I would like to ask whether this place need to add another smp_wmb() to match the smp_rmb() in the object_exist(). I learned that rcu has a publish and subscribe mechanism ;-)
> out: > raw_spin_unlock_irqrestore(&trace_obj_lock, flags); > } > > static bool object_exist(void *obj) > { > ... > max = num_traced_obj; > smp_rmb(); // then the num_traced_obj will cap the max. > for (i = 0; i < max; i++) { > if (traced_obj[i].obj == obj) > return true; > } > return false; > } > > static inline void free_object_pool(void) > { > num_traced_obj = 0; > memset(traced_obj, 0, sizeof(traced_obj)); > } > > Sorry if I confuse you but I think you shouldn't take a time on those unneeded > complexity. :)
Thanks, at least I learned a different way to implement it ;-)
> > > > > > +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 obj; > > > > + long disabled; > > > > + int cpu, n; > > > > + > > > > + preempt_disable_notrace(); > > > > + > > > > + cpu = raw_smp_processor_id(); > > > > + disabled = atomic_inc_return(&per_cpu(trace_object_event_disable, cpu)); > > > > > > So what is the purpose of this check? (are there any issue if the same > > > cpu reenter here?) > > > > > > > There may be an interrupt context that can preempt it. I am not yet > > sure whether the cpu reenter will affect it. > > I will debug and test it. (Referred from function_test_events_call()) > > Maybe you can use ftrace_test_recursion_trylock(), as kprobe_ftrace_handler() > does.
I will use it ,thanks.
> > Thank you, > > -- > Masami Hiramatsu <mhiramat@kernel.org> --- JeffXie
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