[PATCH v2] tracing/uprobes: Support ftrace_event_file base multibuffer

[PATCH v2] tracing/uprobes: Support ftrace_event_file base multibuffer

[zhangwei(Jovi)]

Support multi-buffer on uprobe-based dynamic events by
using ftrace_event_file.

This patch is based kprobe-based dynamic events multibuffer
support work initially, commited by Masami(commit 41a7dd420c),
but revised as below:

Oleg changed the kprobe-based multibuffer design from
array-pointers of ftrace_event_file into simple list,
so this patch also change to the list degisn.

rcu_read_lock/unlock added into uprobe_trace_func/uretprobe_trace_func,
to synchronize with ftrace_event_file list add and delete.

Even though we allow multi-uprobes instances now,
but TP_FLAG_PROFILE/TP_FLAG_TRACE are still mutually exclusive in
probe_event_enable currently, this means we cannot allow
one user is using uprobe-tracer, and another user is using
perf-probe on same uprobe at same time.
(Perhaps this will be fix in future)

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
---
 kernel/trace/trace_uprobe.c |  132 +++++++++++++++++++++++++++++++++++--------
 1 file changed, 110 insertions(+), 22 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 32494fb0..292c39a 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -53,6 +53,7 @@ struct trace_uprobe {
 	struct list_head		list;
 	struct ftrace_event_class	class;
 	struct ftrace_event_call	call;
+	struct list_head		files;
 	struct trace_uprobe_filter	filter;
 	struct uprobe_consumer		consumer;
 	struct inode			*inode;
@@ -65,6 +66,11 @@ struct trace_uprobe {
 	struct probe_arg		args[];
 };

+struct event_file_link {
+	struct ftrace_event_file	*file;
+	struct list_head		list;
+};
+
 #define SIZEOF_TRACE_UPROBE(n)			\
 	(offsetof(struct trace_uprobe, args) +	\
 	(sizeof(struct probe_arg) * (n)))
@@ -124,6 +130,7 @@ alloc_trace_uprobe(const char *group, const char *event, int nargs, bool is_ret)
 		goto error;

 	INIT_LIST_HEAD(&tu->list);
+	INIT_LIST_HEAD(&tu->files);
 	tu->consumer.handler = uprobe_dispatcher;
 	if (is_ret)
 		tu->consumer.ret_handler = uretprobe_dispatcher;
@@ -511,7 +518,8 @@ static const struct file_operations uprobe_profile_ops = {
 };

 static void uprobe_trace_print(struct trace_uprobe *tu,
-				unsigned long func, struct pt_regs *regs)
+				unsigned long func, struct pt_regs *regs,
+				struct ftrace_event_file *ftrace_file)
 {
 	struct uprobe_trace_entry_head *entry;
 	struct ring_buffer_event *event;
@@ -520,9 +528,15 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
 	int size, i;
 	struct ftrace_event_call *call = &tu->call;

+	WARN_ON(call != ftrace_file->event_call);
+
+	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
+		return;
+
 	size = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
-	event = trace_current_buffer_lock_reserve(&buffer, call->event.type,
-						  size + tu->size, 0, 0);
+	event = trace_event_buffer_lock_reserve(&buffer, ftrace_file,
+						call->event.type,
+						size + tu->size, 0, 0);
 	if (!event)
 		return;

@@ -546,15 +560,32 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
 /* uprobe handler */
 static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
 {
-	if (!is_ret_probe(tu))
-		uprobe_trace_print(tu, 0, regs);
+	struct event_file_link *link;
+
+	if (is_ret_probe(tu))
+		return 0;
+
+	rcu_read_lock();
+
+	list_for_each_entry(link, &tu->files, list)
+		uprobe_trace_print(tu, 0, regs, link->file);
+
+	rcu_read_unlock();
+
 	return 0;
 }

 static void uretprobe_trace_func(struct trace_uprobe *tu, unsigned long func,
 				struct pt_regs *regs)
 {
-	uprobe_trace_print(tu, func, regs);
+	struct event_file_link *link;
+
+	rcu_read_lock();
+
+	list_for_each_entry(link, &tu->files, list)
+		uprobe_trace_print(tu, func, regs, link->file);
+
+	rcu_read_unlock();
 }

 /* Event entry printers */
@@ -605,33 +636,89 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self,
 				struct mm_struct *mm);

 static int
-probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
+probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
+		   filter_func_t filter)
 {
+	int enabled = 0;
 	int ret = 0;

-	if (is_trace_uprobe_enabled(tu))
+	/*
+	 * Currently TP_FLAG_TRACE/TP_FLAG_PROFILE are mutually exclusive
+	 * for uprobe(filter argument issue), this need to fix in future.
+	 */
+	if ((file && (tu->flags & TP_FLAG_PROFILE)) ||
+	    (!file && (tu->flags & TP_FLAG_TRACE)))
 		return -EINTR;

+	/* Currently we cannot call uprobe_register twice for same tu */
+	if (is_trace_uprobe_enabled(tu))
+		enabled = 1;
+
+	if (file) {
+		struct event_file_link *link;
+
+		link = kmalloc(sizeof(*link), GFP_KERNEL);
+		if (!link)
+			return -ENOMEM;
+
+		link->file = file;
+		list_add_rcu(&link->list, &tu->files);
+
+		tu->flags |= TP_FLAG_TRACE;
+	} else
+		tu->flags |= TP_FLAG_PROFILE;
+
 	WARN_ON(!uprobe_filter_is_empty(&tu->filter));

-	tu->flags |= flag;
-	tu->consumer.filter = filter;
-	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
-	if (ret)
-		tu->flags &= ~flag;
+	if (!enabled) {
+		tu->consumer.filter = filter;
+		ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
+		if (ret)
+			tu->flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
+	}

 	return ret;
 }

-static void probe_event_disable(struct trace_uprobe *tu, int flag)
+static struct event_file_link *
+find_event_file_link(struct trace_uprobe *tu, struct ftrace_event_file *file)
 {
-	if (!is_trace_uprobe_enabled(tu))
-		return;
+	struct event_file_link *link;
+
+	list_for_each_entry(link, &tu->files, list)
+		if (link->file == file)
+			return link;
+
+	return NULL;
+}
+
+static void
+probe_event_disable(struct trace_uprobe *tu, struct ftrace_event_file *file)
+{
+	if (file) {
+		struct event_file_link *link;
+
+		link = find_event_file_link(tu, file);
+		if (!link)
+			return;
+
+		list_del_rcu(&link->list);
+		/* synchronize with uprobe_trace_func/uretprobe_trace_func */
+		synchronize_sched();
+		kfree(link);
+
+		if (!list_empty(&tu->files))
+			return;
+
+		tu->flags &= ~TP_FLAG_TRACE;
+	} else
+		tu->flags &= ~TP_FLAG_PROFILE;
+

 	WARN_ON(!uprobe_filter_is_empty(&tu->filter));

-	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
-	tu->flags &= ~flag;
+	if (!is_trace_uprobe_enabled(tu))
+		uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
 }

 static int uprobe_event_define_fields(struct ftrace_event_call *event_call)
@@ -867,21 +954,22 @@ static
 int trace_uprobe_register(struct ftrace_event_call *event, enum trace_reg type, void *data)
 {
 	struct trace_uprobe *tu = event->data;
+	struct ftrace_event_file *file = data;

 	switch (type) {
 	case TRACE_REG_REGISTER:
-		return probe_event_enable(tu, TP_FLAG_TRACE, NULL);
+		return probe_event_enable(tu, file, NULL);

 	case TRACE_REG_UNREGISTER:
-		probe_event_disable(tu, TP_FLAG_TRACE);
+		probe_event_disable(tu, file);
 		return 0;

 #ifdef CONFIG_PERF_EVENTS
 	case TRACE_REG_PERF_REGISTER:
-		return probe_event_enable(tu, TP_FLAG_PROFILE, uprobe_perf_filter);
+		return probe_event_enable(tu, NULL, uprobe_perf_filter);

 	case TRACE_REG_PERF_UNREGISTER:
-		probe_event_disable(tu, TP_FLAG_PROFILE);
+		probe_event_disable(tu, NULL);
 		return 0;

 	case TRACE_REG_PERF_OPEN:
-- 
1.7.9.7

Re: [PATCH v2] tracing/uprobes: Support ftrace_event_file base multibuffer

[Masami Hiramatsu]

(2013/06/24 15:54), zhangwei(Jovi) wrote:
> Support multi-buffer on uprobe-based dynamic events by
> using ftrace_event_file.
> 
> This patch is based kprobe-based dynamic events multibuffer
> support work initially, commited by Masami(commit 41a7dd420c),
> but revised as below:
> 
> Oleg changed the kprobe-based multibuffer design from
> array-pointers of ftrace_event_file into simple list,
> so this patch also change to the list degisn.
> 
> rcu_read_lock/unlock added into uprobe_trace_func/uretprobe_trace_func,
> to synchronize with ftrace_event_file list add and delete.
> 
> Even though we allow multi-uprobes instances now,
> but TP_FLAG_PROFILE/TP_FLAG_TRACE are still mutually exclusive in
> probe_event_enable currently, this means we cannot allow
> one user is using uprobe-tracer, and another user is using
> perf-probe on same uprobe at same time.
> (Perhaps this will be fix in future)

Oh... BTW, in the early stage, kprobe-tracer also has same
limitation and fixed by commit 50d78056.

> 
> Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@huawei.com>
> Cc: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Oleg Nesterov <oleg@redhat.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
>  kernel/trace/trace_uprobe.c |  132 +++++++++++++++++++++++++++++++++++--------
>  1 file changed, 110 insertions(+), 22 deletions(-)
> 
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 32494fb0..292c39a 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -53,6 +53,7 @@ struct trace_uprobe {
>  	struct list_head		list;
>  	struct ftrace_event_class	class;
>  	struct ftrace_event_call	call;
> +	struct list_head		files;
>  	struct trace_uprobe_filter	filter;
>  	struct uprobe_consumer		consumer;
>  	struct inode			*inode;
> @@ -65,6 +66,11 @@ struct trace_uprobe {
>  	struct probe_arg		args[];
>  };
> 
> +struct event_file_link {
> +	struct ftrace_event_file	*file;
> +	struct list_head		list;
> +};
> +
>  #define SIZEOF_TRACE_UPROBE(n)			\
>  	(offsetof(struct trace_uprobe, args) +	\
>  	(sizeof(struct probe_arg) * (n)))
> @@ -124,6 +130,7 @@ alloc_trace_uprobe(const char *group, const char *event, int nargs, bool is_ret)
>  		goto error;
> 
>  	INIT_LIST_HEAD(&tu->list);
> +	INIT_LIST_HEAD(&tu->files);
>  	tu->consumer.handler = uprobe_dispatcher;
>  	if (is_ret)
>  		tu->consumer.ret_handler = uretprobe_dispatcher;
> @@ -511,7 +518,8 @@ static const struct file_operations uprobe_profile_ops = {
>  };
> 
>  static void uprobe_trace_print(struct trace_uprobe *tu,
> -				unsigned long func, struct pt_regs *regs)
> +				unsigned long func, struct pt_regs *regs,
> +				struct ftrace_event_file *ftrace_file)
>  {
>  	struct uprobe_trace_entry_head *entry;
>  	struct ring_buffer_event *event;
> @@ -520,9 +528,15 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
>  	int size, i;
>  	struct ftrace_event_call *call = &tu->call;
> 
> +	WARN_ON(call != ftrace_file->event_call);
> +
> +	if (test_bit(FTRACE_EVENT_FL_SOFT_DISABLED_BIT, &ftrace_file->flags))
> +		return;

One note, here you added "soft disabling support" which is different
from multibuffer support. It would be nice to note this in patch
description or make a separated patch.

Other parts look good for me :)

Reviewed-by : Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>

Thank you,

> +
>  	size = SIZEOF_TRACE_ENTRY(is_ret_probe(tu));
> -	event = trace_current_buffer_lock_reserve(&buffer, call->event.type,
> -						  size + tu->size, 0, 0);
> +	event = trace_event_buffer_lock_reserve(&buffer, ftrace_file,
> +						call->event.type,
> +						size + tu->size, 0, 0);
>  	if (!event)
>  		return;
> 
> @@ -546,15 +560,32 @@ static void uprobe_trace_print(struct trace_uprobe *tu,
>  /* uprobe handler */
>  static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  {
> -	if (!is_ret_probe(tu))
> -		uprobe_trace_print(tu, 0, regs);
> +	struct event_file_link *link;
> +
> +	if (is_ret_probe(tu))
> +		return 0;
> +
> +	rcu_read_lock();
> +
> +	list_for_each_entry(link, &tu->files, list)
> +		uprobe_trace_print(tu, 0, regs, link->file);
> +
> +	rcu_read_unlock();
> +
>  	return 0;
>  }
> 
>  static void uretprobe_trace_func(struct trace_uprobe *tu, unsigned long func,
>  				struct pt_regs *regs)
>  {
> -	uprobe_trace_print(tu, func, regs);
> +	struct event_file_link *link;
> +
> +	rcu_read_lock();
> +
> +	list_for_each_entry(link, &tu->files, list)
> +		uprobe_trace_print(tu, func, regs, link->file);
> +
> +	rcu_read_unlock();
>  }
> 
>  /* Event entry printers */
> @@ -605,33 +636,89 @@ typedef bool (*filter_func_t)(struct uprobe_consumer *self,
>  				struct mm_struct *mm);
> 
>  static int
> -probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
> +probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
> +		   filter_func_t filter)
>  {
> +	int enabled = 0;
>  	int ret = 0;
> 
> -	if (is_trace_uprobe_enabled(tu))
> +	/*
> +	 * Currently TP_FLAG_TRACE/TP_FLAG_PROFILE are mutually exclusive
> +	 * for uprobe(filter argument issue), this need to fix in future.
> +	 */
> +	if ((file && (tu->flags & TP_FLAG_PROFILE)) ||
> +	    (!file && (tu->flags & TP_FLAG_TRACE)))
>  		return -EINTR;
> 
> +	/* Currently we cannot call uprobe_register twice for same tu */
> +	if (is_trace_uprobe_enabled(tu))
> +		enabled = 1;
> +
> +	if (file) {
> +		struct event_file_link *link;
> +
> +		link = kmalloc(sizeof(*link), GFP_KERNEL);
> +		if (!link)
> +			return -ENOMEM;
> +
> +		link->file = file;
> +		list_add_rcu(&link->list, &tu->files);
> +
> +		tu->flags |= TP_FLAG_TRACE;
> +	} else
> +		tu->flags |= TP_FLAG_PROFILE;
> +
>  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> 
> -	tu->flags |= flag;
> -	tu->consumer.filter = filter;
> -	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> -	if (ret)
> -		tu->flags &= ~flag;
> +	if (!enabled) {
> +		tu->consumer.filter = filter;
> +		ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> +		if (ret)
> +			tu->flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
> +	}
> 
>  	return ret;
>  }
> 
> -static void probe_event_disable(struct trace_uprobe *tu, int flag)
> +static struct event_file_link *
> +find_event_file_link(struct trace_uprobe *tu, struct ftrace_event_file *file)
>  {
> -	if (!is_trace_uprobe_enabled(tu))
> -		return;
> +	struct event_file_link *link;
> +
> +	list_for_each_entry(link, &tu->files, list)
> +		if (link->file == file)
> +			return link;
> +
> +	return NULL;
> +}
> +
> +static void
> +probe_event_disable(struct trace_uprobe *tu, struct ftrace_event_file *file)
> +{
> +	if (file) {
> +		struct event_file_link *link;
> +
> +		link = find_event_file_link(tu, file);
> +		if (!link)
> +			return;
> +
> +		list_del_rcu(&link->list);
> +		/* synchronize with uprobe_trace_func/uretprobe_trace_func */
> +		synchronize_sched();
> +		kfree(link);
> +
> +		if (!list_empty(&tu->files))
> +			return;
> +
> +		tu->flags &= ~TP_FLAG_TRACE;
> +	} else
> +		tu->flags &= ~TP_FLAG_PROFILE;
> +
> 
>  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> 
> -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> -	tu->flags &= ~flag;
> +	if (!is_trace_uprobe_enabled(tu))
> +		uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
>  }
> 
>  static int uprobe_event_define_fields(struct ftrace_event_call *event_call)
> @@ -867,21 +954,22 @@ static
>  int trace_uprobe_register(struct ftrace_event_call *event, enum trace_reg type, void *data)
>  {
>  	struct trace_uprobe *tu = event->data;
> +	struct ftrace_event_file *file = data;
> 
>  	switch (type) {
>  	case TRACE_REG_REGISTER:
> -		return probe_event_enable(tu, TP_FLAG_TRACE, NULL);
> +		return probe_event_enable(tu, file, NULL);
> 
>  	case TRACE_REG_UNREGISTER:
> -		probe_event_disable(tu, TP_FLAG_TRACE);
> +		probe_event_disable(tu, file);
>  		return 0;
> 
>  #ifdef CONFIG_PERF_EVENTS
>  	case TRACE_REG_PERF_REGISTER:
> -		return probe_event_enable(tu, TP_FLAG_PROFILE, uprobe_perf_filter);
> +		return probe_event_enable(tu, NULL, uprobe_perf_filter);
> 
>  	case TRACE_REG_PERF_UNREGISTER:
> -		probe_event_disable(tu, TP_FLAG_PROFILE);
> +		probe_event_disable(tu, NULL);
>  		return 0;
> 
>  	case TRACE_REG_PERF_OPEN:
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@hitachi.com

Re: [PATCH v2] tracing/uprobes: Support ftrace_event_file base multibuffer

[Oleg Nesterov]

Hi Jovi,

I'll try to read this patch carefully tomorrow.

Looks fine at first glance, but some nits below.

On 06/24, zhangwei(Jovi) wrote:
>
>  static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>  {
> -	if (!is_ret_probe(tu))
> -		uprobe_trace_print(tu, 0, regs);
> +	struct event_file_link *link;
> +
> +	if (is_ret_probe(tu))
> +		return 0;
> +
> +	rcu_read_lock();
> +
> +	list_for_each_entry(link, &tu->files, list)
> +		uprobe_trace_print(tu, 0, regs, link->file);
> +
> +	rcu_read_unlock();

Purely cosmetic and I won't argue, but why the empty lines around
list_for_each_entry() ?

>  static int
> -probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
> +probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
> +		   filter_func_t filter)
>  {
> +	int enabled = 0;
>  	int ret = 0;
> 
> -	if (is_trace_uprobe_enabled(tu))
> +	/*
> +	 * Currently TP_FLAG_TRACE/TP_FLAG_PROFILE are mutually exclusive
> +	 * for uprobe(filter argument issue), this need to fix in future.
> +	 */
> +	if ((file && (tu->flags & TP_FLAG_PROFILE)) ||
> +	    (!file && (tu->flags & TP_FLAG_TRACE)))
>  		return -EINTR;

Well, this looks confusing and overcomplicated, see below.

> +	/* Currently we cannot call uprobe_register twice for same tu */
> +	if (is_trace_uprobe_enabled(tu))
> +		enabled = 1;

The comment is wrong. It is not that we can't do this "Currently".

We must not do uprobe_register(..., consumer) twice, consumer/uprobe
are linked together.

> +	if (file) {
> +		struct event_file_link *link;
> +

Just add
		if (TP_FLAG_PROFILE)
			return -EINTR;

here and kill the complicated check below. Same for the "else" branch.

> +static void
> +probe_event_disable(struct trace_uprobe *tu, struct ftrace_event_file *file)
> +{
> +	if (file) {
> +		struct event_file_link *link;
> +
> +		link = find_event_file_link(tu, file);
> +		if (!link)
> +			return;
> +
> +		list_del_rcu(&link->list);
> +		/* synchronize with uprobe_trace_func/uretprobe_trace_func */
> +		synchronize_sched();
> +		kfree(link);
> +
> +		if (!list_empty(&tu->files))
> +			return;
> +
> +		tu->flags &= ~TP_FLAG_TRACE;
> +	} else
> +		tu->flags &= ~TP_FLAG_PROFILE;
> +
> 
>  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
> 
> -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> -	tu->flags &= ~flag;
> +	if (!is_trace_uprobe_enabled(tu))
> +		uprobe_unregister(tu->inode, tu->offset, &tu->consumer);

Well, this is not exactly right... Currently this is fine, but still.

It would be better to clear TP_FLAG_TRACE/TP_FLAG_PROFILE after
uprobe_unregister(), when we can't race with the running handler
which can check ->flags.

And I'd suggest you to send the soft-enable/disable change in a
separate (and trivial) patch.

Oleg.

Re: [PATCH v2] tracing/uprobes: Support ftrace_event_file base multibuffer

[Oleg Nesterov]

forgot to mention,

On 06/24, Oleg Nesterov wrote:
>
> > +	/*
> > +	 * Currently TP_FLAG_TRACE/TP_FLAG_PROFILE are mutually exclusive
> > +	 * for uprobe(filter argument issue), this need to fix in future.
                      ^^^^^^^^^^^^^^^^^^^^^

Just in case, this is not that simple.

For example, suppose that TRACE_REG_REGISTER comes after
TRACE_REG_PERF_REGISTER. In this case we need uprobe_perf_open-like
code to establish nr_systemwide != 0 and do uprobe_apply() if
necessary.

Oleg.

Re: [PATCH v2] tracing/uprobes: Support ftrace_event_file base multibuffer

[zhangwei(Jovi)]

On 2013/6/25 2:05, Oleg Nesterov wrote:
> Hi Jovi,
> 
> I'll try to read this patch carefully tomorrow.
> 
> Looks fine at first glance, but some nits below.
> 
> On 06/24, zhangwei(Jovi) wrote:
>>
>>  static int uprobe_trace_func(struct trace_uprobe *tu, struct pt_regs *regs)
>>  {
>> -	if (!is_ret_probe(tu))
>> -		uprobe_trace_print(tu, 0, regs);
>> +	struct event_file_link *link;
>> +
>> +	if (is_ret_probe(tu))
>> +		return 0;
>> +
>> +	rcu_read_lock();
>> +
>> +	list_for_each_entry(link, &tu->files, list)
>> +		uprobe_trace_print(tu, 0, regs, link->file);
>> +
>> +	rcu_read_unlock();
> 
> Purely cosmetic and I won't argue, but why the empty lines around
> list_for_each_entry() ?
> 
>>  static int
>> -probe_event_enable(struct trace_uprobe *tu, int flag, filter_func_t filter)
>> +probe_event_enable(struct trace_uprobe *tu, struct ftrace_event_file *file,
>> +		   filter_func_t filter)
>>  {
>> +	int enabled = 0;
>>  	int ret = 0;
>>
>> -	if (is_trace_uprobe_enabled(tu))
>> +	/*
>> +	 * Currently TP_FLAG_TRACE/TP_FLAG_PROFILE are mutually exclusive
>> +	 * for uprobe(filter argument issue), this need to fix in future.
>> +	 */
>> +	if ((file && (tu->flags & TP_FLAG_PROFILE)) ||
>> +	    (!file && (tu->flags & TP_FLAG_TRACE)))
>>  		return -EINTR;
> 
> Well, this looks confusing and overcomplicated, see below.
> 
>> +	/* Currently we cannot call uprobe_register twice for same tu */
>> +	if (is_trace_uprobe_enabled(tu))
>> +		enabled = 1;
> 
> The comment is wrong. It is not that we can't do this "Currently".
> 
> We must not do uprobe_register(..., consumer) twice, consumer/uprobe
> are linked together.
> 
>> +	if (file) {
>> +		struct event_file_link *link;
>> +
> 
> Just add
> 		if (TP_FLAG_PROFILE)
> 			return -EINTR;
> 
> here and kill the complicated check below. Same for the "else" branch.
> 
>> +static void
>> +probe_event_disable(struct trace_uprobe *tu, struct ftrace_event_file *file)
>> +{
>> +	if (file) {
>> +		struct event_file_link *link;
>> +
>> +		link = find_event_file_link(tu, file);
>> +		if (!link)
>> +			return;
>> +
>> +		list_del_rcu(&link->list);
>> +		/* synchronize with uprobe_trace_func/uretprobe_trace_func */
>> +		synchronize_sched();
>> +		kfree(link);
>> +
>> +		if (!list_empty(&tu->files))
>> +			return;
>> +
>> +		tu->flags &= ~TP_FLAG_TRACE;
>> +	} else
>> +		tu->flags &= ~TP_FLAG_PROFILE;
>> +
>>
>>  	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>>
>> -	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
>> -	tu->flags &= ~flag;
>> +	if (!is_trace_uprobe_enabled(tu))
>> +		uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> 
> Well, this is not exactly right... Currently this is fine, but still.
> 
> It would be better to clear TP_FLAG_TRACE/TP_FLAG_PROFILE after
> uprobe_unregister(), when we can't race with the running handler
> which can check ->flags.
> 
> And I'd suggest you to send the soft-enable/disable change in a
> separate (and trivial) patch.
> 
> Oleg.
Thanks Oleg, you are right, please check v3 patch.

.jovi