[PATCH v2 0/1] tracing: trace_remove_event_call() should fail if call/file is in use

[PATCH v2 0/1] tracing: trace_remove_event_call() should fail if call/file is in use

[Oleg Nesterov]

Hello.

On top of "[PATCH v2 0/6] tracing: open/delete fixes" series.

Perhaps this series should be updated, Masami has some concerns.
But it seems that you both mostly agree with these changes, so
let me send the "last" patch for review.

The last change in kernel/trace/trace_events.c we need to close the
problems with create/use/delete (at least those which I know ;).

Now we are ready to change trace_kprobe.c and trace_uprobe.c, Steven
already has the patches.

Changes:

	- remove the TRACE_EVENT_FL_REF_MASK (which we do not have)
	  check.

	  We rely on the previous changes, we do not care if someone
	  have an opened file, event_enable_write/etc can do nothing
	  but fail after we do remove_event_file_dir().

	- Add the comment and a note into the changelog to explain
	  why we still need to check FTRACE_EVENT_FL_ENABLED.

Oleg.

 include/linux/ftrace_event.h |    2 +-
 kernel/trace/trace_events.c  |   35 +++++++++++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 3 deletions(-)

[PATCH v2 1/1] tracing: trace_remove_event_call() should fail if call/file is in use

[Oleg Nesterov]

Change trace_remove_event_call(call) to return the error if this
call is active. This is what the callers assume but can't verify
outside of the tracing locks. Both trace_kprobe.c/trace_uprobe.c
need the additional changes, unregister_trace_probe() should abort
if trace_remove_event_call() fails.

The caller is going to free this call/file so we must ensure that
nobody can use them after trace_remove_event_call() succeeds.
debugfs should be fine after the previous changes and event_remove()
does TRACE_REG_UNREGISTER, but still there are 2 reasons why we need
the additional checks:

- There could be a perf_event(s) attached to this tp_event, so the
  patch checks ->perf_refcount.

- TRACE_REG_UNREGISTER can be suppressed by FTRACE_EVENT_FL_SOFT_MODE,
  so we simply check FTRACE_EVENT_FL_ENABLED protected by event_mutex.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/ftrace_event.h |    2 +-
 kernel/trace/trace_events.c  |   35 +++++++++++++++++++++++++++++++++--
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
index 4372658..f98ab06 100644
--- a/include/linux/ftrace_event.h
+++ b/include/linux/ftrace_event.h
@@ -332,7 +332,7 @@ extern int trace_define_field(struct ftrace_event_call *call, const char *type,
 			      const char *name, int offset, int size,
 			      int is_signed, int filter_type);
 extern int trace_add_event_call(struct ftrace_event_call *call);
-extern void trace_remove_event_call(struct ftrace_event_call *call);
+extern int trace_remove_event_call(struct ftrace_event_call *call);
 
 #define is_signed_type(type)	(((type)(-1)) < (type)1)
 
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 79a2743..3450496 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -1709,16 +1709,47 @@ static void __trace_remove_event_call(struct ftrace_event_call *call)
 	destroy_preds(call);
 }
 
+static int probe_remove_event_call(struct ftrace_event_call *call)
+{
+	struct trace_array *tr;
+	struct ftrace_event_file *file;
+
+#ifdef CONFIG_PERF_EVENTS
+	if (call->perf_refcount)
+		return -EBUSY;
+#endif
+	do_for_each_event_file(tr, file) {
+		if (file->event_call != call)
+			continue;
+		/*
+		 * We can't rely on ftrace_event_enable_disable(enable => 0)
+		 * we are going to do, FTRACE_EVENT_FL_SOFT_MODE can suppress
+		 * TRACE_REG_UNREGISTER.
+		 */
+		if (file->flags & FTRACE_EVENT_FL_ENABLED)
+			return -EBUSY;
+		break;
+	} while_for_each_event_file();
+
+	__trace_remove_event_call(call);
+
+	return 0;
+}
+
 /* Remove an event_call */
-void trace_remove_event_call(struct ftrace_event_call *call)
+int trace_remove_event_call(struct ftrace_event_call *call)
 {
+	int ret;
+
 	mutex_lock(&trace_types_lock);
 	mutex_lock(&event_mutex);
 	down_write(&trace_event_sem);
-	__trace_remove_event_call(call);
+	ret = probe_remove_event_call(call);
 	up_write(&trace_event_sem);
 	mutex_unlock(&event_mutex);
 	mutex_unlock(&trace_types_lock);
+
+	return ret;
 }
 
 #define for_each_event(event, start, end)			\
-- 
1.5.5.1

Re: [PATCH v2 1/1] tracing: trace_remove_event_call() should fail if call/file is in use

[Masami Hiramatsu]

(2013/07/30 2:50), Oleg Nesterov wrote:
> Change trace_remove_event_call(call) to return the error if this
> call is active. This is what the callers assume but can't verify
> outside of the tracing locks. Both trace_kprobe.c/trace_uprobe.c
> need the additional changes, unregister_trace_probe() should abort
> if trace_remove_event_call() fails.
> 
> The caller is going to free this call/file so we must ensure that
> nobody can use them after trace_remove_event_call() succeeds.
> debugfs should be fine after the previous changes and event_remove()
> does TRACE_REG_UNREGISTER, but still there are 2 reasons why we need
> the additional checks:
> 
> - There could be a perf_event(s) attached to this tp_event, so the
>   patch checks ->perf_refcount.
> 
> - TRACE_REG_UNREGISTER can be suppressed by FTRACE_EVENT_FL_SOFT_MODE,
>   so we simply check FTRACE_EVENT_FL_ENABLED protected by event_mutex.
> 

This looks good to me :)

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

Thanks! I'll update trace_kprobes.c too.

> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
>  include/linux/ftrace_event.h |    2 +-
>  kernel/trace/trace_events.c  |   35 +++++++++++++++++++++++++++++++++--
>  2 files changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h
> index 4372658..f98ab06 100644
> --- a/include/linux/ftrace_event.h
> +++ b/include/linux/ftrace_event.h
> @@ -332,7 +332,7 @@ extern int trace_define_field(struct ftrace_event_call *call, const char *type,
>  			      const char *name, int offset, int size,
>  			      int is_signed, int filter_type);
>  extern int trace_add_event_call(struct ftrace_event_call *call);
> -extern void trace_remove_event_call(struct ftrace_event_call *call);
> +extern int trace_remove_event_call(struct ftrace_event_call *call);
>  
>  #define is_signed_type(type)	(((type)(-1)) < (type)1)
>  
> diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
> index 79a2743..3450496 100644
> --- a/kernel/trace/trace_events.c
> +++ b/kernel/trace/trace_events.c
> @@ -1709,16 +1709,47 @@ static void __trace_remove_event_call(struct ftrace_event_call *call)
>  	destroy_preds(call);
>  }
>  
> +static int probe_remove_event_call(struct ftrace_event_call *call)
> +{
> +	struct trace_array *tr;
> +	struct ftrace_event_file *file;
> +
> +#ifdef CONFIG_PERF_EVENTS
> +	if (call->perf_refcount)
> +		return -EBUSY;
> +#endif
> +	do_for_each_event_file(tr, file) {
> +		if (file->event_call != call)
> +			continue;
> +		/*
> +		 * We can't rely on ftrace_event_enable_disable(enable => 0)
> +		 * we are going to do, FTRACE_EVENT_FL_SOFT_MODE can suppress
> +		 * TRACE_REG_UNREGISTER.
> +		 */
> +		if (file->flags & FTRACE_EVENT_FL_ENABLED)
> +			return -EBUSY;
> +		break;
> +	} while_for_each_event_file();
> +
> +	__trace_remove_event_call(call);
> +
> +	return 0;
> +}
> +
>  /* Remove an event_call */
> -void trace_remove_event_call(struct ftrace_event_call *call)
> +int trace_remove_event_call(struct ftrace_event_call *call)
>  {
> +	int ret;
> +
>  	mutex_lock(&trace_types_lock);
>  	mutex_lock(&event_mutex);
>  	down_write(&trace_event_sem);
> -	__trace_remove_event_call(call);
> +	ret = probe_remove_event_call(call);
>  	up_write(&trace_event_sem);
>  	mutex_unlock(&event_mutex);
>  	mutex_unlock(&trace_types_lock);
> +
> +	return ret;
>  }
>  
>  #define for_each_event(event, start, end)			\
> 


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

Re: [PATCH v2 1/1] tracing: trace_remove_event_call() should fail if call/file is in use

[Steven Rostedt]

On Mon, 2013-07-29 at 19:50 +0200, Oleg Nesterov wrote:
>  
> +static int probe_remove_event_call(struct ftrace_event_call *call)
> +{
> +	struct trace_array *tr;
> +	struct ftrace_event_file *file;
> +
> +#ifdef CONFIG_PERF_EVENTS
> +	if (call->perf_refcount)
> +		return -EBUSY;
> +#endif
> +	do_for_each_event_file(tr, file) {
> +		if (file->event_call != call)
> +			continue;
> +		/*
> +		 * We can't rely on ftrace_event_enable_disable(enable => 0)
> +		 * we are going to do, FTRACE_EVENT_FL_SOFT_MODE can suppress
> +		 * TRACE_REG_UNREGISTER.
> +		 */
> +		if (file->flags & FTRACE_EVENT_FL_ENABLED)
> +			return -EBUSY;
> +		break;

I'm going to modify the patch to include a comment here about the break
being used to go to the next trace_array and not leaving the loop.

-- Steve

> +	} while_for_each_event_file();
> +
> +	__trace_remove_event_call(call);
> +
> +	return 0;
> +}
> +
>  /* Remove an event_call */
> -void trace_remove_event_call(struct ftrace_event_call *call)
> +int trace_remove_event_call(struct ftrace_event_call *call)
>  {
> +	int ret;
> +
>  	mutex_lock(&trace_types_lock);
>  	mutex_lock(&event_mutex);
>  	down_write(&trace_event_sem);
> -	__trace_remove_event_call(call);
> +	ret = probe_remove_event_call(call);
>  	up_write(&trace_event_sem);
>  	mutex_unlock(&event_mutex);
>  	mutex_unlock(&trace_types_lock);
> +
> +	return ret;
>  }
>  
>  #define for_each_event(event, start, end)			\

Re: [PATCH v2 1/1] tracing: trace_remove_event_call() should fail if call/file is in use

[Steven Rostedt]

On Wed, 2013-07-31 at 12:50 -0400, Steven Rostedt wrote:
> On Mon, 2013-07-29 at 19:50 +0200, Oleg Nesterov wrote:
> >  
> > +static int probe_remove_event_call(struct ftrace_event_call *call)
> > +{
> > +	struct trace_array *tr;
> > +	struct ftrace_event_file *file;
> > +
> > +#ifdef CONFIG_PERF_EVENTS
> > +	if (call->perf_refcount)
> > +		return -EBUSY;
> > +#endif
> > +	do_for_each_event_file(tr, file) {
> > +		if (file->event_call != call)
> > +			continue;
> > +		/*
> > +		 * We can't rely on ftrace_event_enable_disable(enable => 0)
> > +		 * we are going to do, FTRACE_EVENT_FL_SOFT_MODE can suppress
> > +		 * TRACE_REG_UNREGISTER.
> > +		 */
> > +		if (file->flags & FTRACE_EVENT_FL_ENABLED)
> > +			return -EBUSY;
> > +		break;
> 
> I'm going to modify the patch to include a comment here about the break
> being used to go to the next trace_array and not leaving the loop.
> 

Screw it, I'm going to just add a separate patch to include it.

-- Steve

Re: [PATCH v2 0/1] tracing: trace_remove_event_call() should fail if call/file is in use

[Steven Rostedt]

On Mon, 2013-07-29 at 19:50 +0200, Oleg Nesterov wrote:
> Hello.
> 
> On top of "[PATCH v2 0/6] tracing: open/delete fixes" series.
> 
> Perhaps this series should be updated, Masami has some concerns.
> But it seems that you both mostly agree with these changes, so
> let me send the "last" patch for review.
> 
> The last change in kernel/trace/trace_events.c we need to close the
> problems with create/use/delete (at least those which I know ;).
> 
> Now we are ready to change trace_kprobe.c and trace_uprobe.c, Steven
> already has the patches.

Can you refresh my memory. My INBOX is quite full. What were the
subjects for these patches? This fix has lots of different threads, not
to mention versions.

Thanks,

-- Steve

> 
> Changes:
> 
> 	- remove the TRACE_EVENT_FL_REF_MASK (which we do not have)
> 	  check.
> 
> 	  We rely on the previous changes, we do not care if someone
> 	  have an opened file, event_enable_write/etc can do nothing
> 	  but fail after we do remove_event_file_dir().
> 
> 	- Add the comment and a note into the changelog to explain
> 	  why we still need to check FTRACE_EVENT_FL_ENABLED.
> 
> Oleg.
> 
>  include/linux/ftrace_event.h |    2 +-
>  kernel/trace/trace_events.c  |   35 +++++++++++++++++++++++++++++++++--
>  2 files changed, 34 insertions(+), 3 deletions(-)

Re: [PATCH v2 0/1] tracing: trace_remove_event_call() should fail if call/file is in use

[Oleg Nesterov]

[-- Attachment #1: Type: text/plain, Size: 606 bytes --]

On 07/31, Steven Rostedt wrote:
>
> On Mon, 2013-07-29 at 19:50 +0200, Oleg Nesterov wrote:
> >
> > Now we are ready to change trace_kprobe.c and trace_uprobe.c, Steven
> > already has the patches.
>
> Can you refresh my memory. My INBOX is quite full. What were the
> subjects for these patches?

Please see the attached mbox. And notice who is the author ;)
I also added the ack from Masami.

But if you only need the subjects:

	[RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open
	[RFC][PATCH 4/4] tracing/uprobes: Fail to unregister if probe event files are open

Oleg.

[-- Attachment #2: old.mbox --]
[-- Type: text/plain, Size: 20101 bytes --]

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Date: Wed, 03 Jul 2013 23:33:50 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Oleg Nesterov <oleg@redhat.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        "zhangwei(Jovi)" <jovi.zhangwei@huawei.com>,
        Jiri Olsa <jolsa@redhat.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
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        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open
References: <20130704033347.807661713@goodmis.org>
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From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

When one of the event files is opened, we need to prevent them from
being removed. Modules do with with the module owner set (automated
from the VFS layer).  The ftrace buffer instances have a ref count added
to the trace_array when the enabled file is opened (the others are not
that big of a deal, as they only reference the event calls which
still exist when an instance disappears). But kprobes and uprobes
do not have any protection.

 # cd /sys/kernel/debug/tracing
 # echo 'p:sigprocmask sigprocmask' > kprobe_events || exit -1
 # enable_probe() {
    sleep 10
    echo 1
 }
 # file=events/kprobes/sigprocmask/enable
 # enable_probe > $file &
 > kprobe_events

The above will corrupt the kprobe system, as the write to the enable
file will happen after the kprobe was deleted.

Trying to create the probe again fails:

 # echo 'p:sigprocmask sigprocmask' > kprobe_events
 # cat kprobe_events
p:kprobes/sigprocmask sigprocmask
 # ls events/kprobes/
enable  filter

Have the unregister probe fail when the event files are open, in use
are used by perf.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace_kprobe.c |   21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 7ed6976..ffcaf42 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -95,7 +95,7 @@ static __kprobes bool trace_probe_is_on_module(struct trace_probe *tp)
 }
 
 static int register_probe_event(struct trace_probe *tp);
-static void unregister_probe_event(struct trace_probe *tp);
+static int unregister_probe_event(struct trace_probe *tp);
 
 static DEFINE_MUTEX(probe_lock);
 static LIST_HEAD(probe_list);
@@ -340,9 +340,12 @@ static int unregister_trace_probe(struct trace_probe *tp)
 	if (trace_probe_is_enabled(tp))
 		return -EBUSY;
 
+	/* Will fail if probe is being used by ftrace or perf */
+	if (unregister_probe_event(tp))
+		return -EBUSY;
+
 	__unregister_trace_probe(tp);
 	list_del(&tp->list);
-	unregister_probe_event(tp);
 
 	return 0;
 }
@@ -621,7 +624,9 @@ static int release_all_trace_probes(void)
 	/* TODO: Use batch unregistration */
 	while (!list_empty(&probe_list)) {
 		tp = list_entry(probe_list.next, struct trace_probe, list);
-		unregister_trace_probe(tp);
+		ret = unregister_trace_probe(tp);
+		if (ret)
+			goto end;
 		free_trace_probe(tp);
 	}
 
@@ -1242,11 +1247,15 @@ static int register_probe_event(struct trace_probe *tp)
 	return ret;
 }
 
-static void unregister_probe_event(struct trace_probe *tp)
+static int unregister_probe_event(struct trace_probe *tp)
 {
+	int ret;
+
 	/* tp->event is unregistered in trace_remove_event_call() */
-	trace_remove_event_call(&tp->call);
-	kfree(tp->call.print_fmt);
+	ret = trace_remove_event_call(&tp->call);
+	if (!ret)
+		kfree(tp->call.print_fmt);
+	return ret;
 }
 
 /* Make a debugfs interface for controlling probe points */
-- 
1.7.10.4



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Message-ID: <51F7762E.7010906@hitachi.com>
Date: Tue, 30 Jul 2013 17:15:42 +0900
From: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
Organization: Hitachi, Ltd., Japan
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To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Oleg Nesterov <oleg@redhat.com>,
        "zhangwei(Jovi)" <jovi.zhangwei@huawei.com>,
        Jiri Olsa <jolsa@redhat.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe
 event files are open
References: <20130704033347.807661713@goodmis.org> <20130704034038.819592356@goodmis.org>
In-Reply-To: <20130704034038.819592356@goodmis.org>
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(2013/07/04 12:33), Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
> 
> When one of the event files is opened, we need to prevent them from
> being removed. Modules do with with the module owner set (automated
> from the VFS layer).  The ftrace buffer instances have a ref count added
> to the trace_array when the enabled file is opened (the others are not
> that big of a deal, as they only reference the event calls which
> still exist when an instance disappears). But kprobes and uprobes
> do not have any protection.
> 
>  # cd /sys/kernel/debug/tracing
>  # echo 'p:sigprocmask sigprocmask' > kprobe_events || exit -1
>  # enable_probe() {
>     sleep 10
>     echo 1
>  }
>  # file=events/kprobes/sigprocmask/enable
>  # enable_probe > $file &
>  > kprobe_events
> 
> The above will corrupt the kprobe system, as the write to the enable
> file will happen after the kprobe was deleted.
> 
> Trying to create the probe again fails:
> 
>  # echo 'p:sigprocmask sigprocmask' > kprobe_events
>  # cat kprobe_events
> p:kprobes/sigprocmask sigprocmask
>  # ls events/kprobes/
> enable  filter
> 
> Have the unregister probe fail when the event files are open, in use
> are used by perf.
> 

Now, since the commit a232e270d makes sure that disable_trace_probe()
waits until all running handlers are done, this patch has no problem.

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

Thank you!


> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
>  kernel/trace/trace_kprobe.c |   21 +++++++++++++++------
>  1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
> index 7ed6976..ffcaf42 100644
> --- a/kernel/trace/trace_kprobe.c
> +++ b/kernel/trace/trace_kprobe.c
> @@ -95,7 +95,7 @@ static __kprobes bool trace_probe_is_on_module(struct trace_probe *tp)
>  }
>  
>  static int register_probe_event(struct trace_probe *tp);
> -static void unregister_probe_event(struct trace_probe *tp);
> +static int unregister_probe_event(struct trace_probe *tp);
>  
>  static DEFINE_MUTEX(probe_lock);
>  static LIST_HEAD(probe_list);
> @@ -340,9 +340,12 @@ static int unregister_trace_probe(struct trace_probe *tp)
>  	if (trace_probe_is_enabled(tp))
>  		return -EBUSY;
>  
> +	/* Will fail if probe is being used by ftrace or perf */
> +	if (unregister_probe_event(tp))
> +		return -EBUSY;
> +
>  	__unregister_trace_probe(tp);
>  	list_del(&tp->list);
> -	unregister_probe_event(tp);
>  
>  	return 0;
>  }
> @@ -621,7 +624,9 @@ static int release_all_trace_probes(void)
>  	/* TODO: Use batch unregistration */
>  	while (!list_empty(&probe_list)) {
>  		tp = list_entry(probe_list.next, struct trace_probe, list);
> -		unregister_trace_probe(tp);
> +		ret = unregister_trace_probe(tp);
> +		if (ret)
> +			goto end;
>  		free_trace_probe(tp);
>  	}
>  
> @@ -1242,11 +1247,15 @@ static int register_probe_event(struct trace_probe *tp)
>  	return ret;
>  }
>  
> -static void unregister_probe_event(struct trace_probe *tp)
> +static int unregister_probe_event(struct trace_probe *tp)
>  {
> +	int ret;
> +
>  	/* tp->event is unregistered in trace_remove_event_call() */
> -	trace_remove_event_call(&tp->call);
> -	kfree(tp->call.print_fmt);
> +	ret = trace_remove_event_call(&tp->call);
> +	if (!ret)
> +		kfree(tp->call.print_fmt);
> +	return ret;
>  }
>  
>  /* Make a debugfs interface for controlling probe points */
> 


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



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Date: Wed, 03 Jul 2013 23:33:51 -0400
From: Steven Rostedt <rostedt@goodmis.org>
To: linux-kernel@vger.kernel.org
Cc: Oleg Nesterov <oleg@redhat.com>,
        Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>,
        "zhangwei(Jovi)" <jovi.zhangwei@huawei.com>,
        Jiri Olsa <jolsa@redhat.com>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Arnaldo Carvalho de Melo <acme@ghostprotocols.net>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Frederic Weisbecker <fweisbec@gmail.com>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: [RFC][PATCH 4/4] tracing/uprobes: Fail to unregister if probe event files are open
References: <20130704033347.807661713@goodmis.org>
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From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>

When one of the event files is opened, we need to prevent them from
being removed. Modules do with with the module owner set (automated
from the VFS layer).  The ftrace buffer instances have a ref count added
to the trace_array when the enabled file is opened (the others are not
that big of a deal, as they only reference the event calls which
still exist when an instance disappears). But kprobes and uprobes
do not have any protection.

Have the unregister probe fail when the event files are open, in use
are used by perf.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace_uprobe.c |   48 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 36 insertions(+), 12 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index d5d0cd3..4916da5 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -70,7 +70,7 @@ struct trace_uprobe {
 	(sizeof(struct probe_arg) * (n)))
 
 static int register_uprobe_event(struct trace_uprobe *tu);
-static void unregister_uprobe_event(struct trace_uprobe *tu);
+static int unregister_uprobe_event(struct trace_uprobe *tu);
 
 static DEFINE_MUTEX(uprobe_lock);
 static LIST_HEAD(uprobe_list);
@@ -164,11 +164,17 @@ static struct trace_uprobe *find_probe_event(const char *event, const char *grou
 }
 
 /* Unregister a trace_uprobe and probe_event: call with locking uprobe_lock */
-static void unregister_trace_uprobe(struct trace_uprobe *tu)
+static int unregister_trace_uprobe(struct trace_uprobe *tu)
 {
+	int ret;
+
+	ret = unregister_uprobe_event(tu);
+	if (ret)
+		return ret;
+
 	list_del(&tu->list);
-	unregister_uprobe_event(tu);
 	free_trace_uprobe(tu);
+	return 0;
 }
 
 /* Register a trace_uprobe and probe_event */
@@ -181,9 +187,12 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
 
 	/* register as an event */
 	old_tp = find_probe_event(tu->call.name, tu->call.class->system);
-	if (old_tp)
+	if (old_tp) {
 		/* delete old event */
-		unregister_trace_uprobe(old_tp);
+		ret = unregister_trace_uprobe(old_tp);
+		if (ret)
+			goto end;
+	}
 
 	ret = register_uprobe_event(tu);
 	if (ret) {
@@ -256,6 +265,8 @@ static int create_trace_uprobe(int argc, char **argv)
 		group = UPROBE_EVENT_SYSTEM;
 
 	if (is_delete) {
+		int ret;
+
 		if (!event) {
 			pr_info("Delete command needs an event name.\n");
 			return -EINVAL;
@@ -269,9 +280,9 @@ static int create_trace_uprobe(int argc, char **argv)
 			return -ENOENT;
 		}
 		/* delete an event */
-		unregister_trace_uprobe(tu);
+		ret = unregister_trace_uprobe(tu);
 		mutex_unlock(&uprobe_lock);
-		return 0;
+		return ret;
 	}
 
 	if (argc < 2) {
@@ -408,16 +419,20 @@ fail_address_parse:
 	return ret;
 }
 
-static void cleanup_all_probes(void)
+static int cleanup_all_probes(void)
 {
 	struct trace_uprobe *tu;
+	int ret = 0;
 
 	mutex_lock(&uprobe_lock);
 	while (!list_empty(&uprobe_list)) {
 		tu = list_entry(uprobe_list.next, struct trace_uprobe, list);
-		unregister_trace_uprobe(tu);
+		ret = unregister_trace_uprobe(tu);
+		if (ret)
+			break;
 	}
 	mutex_unlock(&uprobe_lock);
+	return ret;
 }
 
 /* Probes listing interfaces */
@@ -462,8 +477,12 @@ static const struct seq_operations probes_seq_op = {
 
 static int probes_open(struct inode *inode, struct file *file)
 {
+	int ret = 0;
+
 	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC))
-		cleanup_all_probes();
+		ret = cleanup_all_probes();
+	if (ret)
+		return ret;
 
 	return seq_open(file, &probes_seq_op);
 }
@@ -970,12 +989,17 @@ static int register_uprobe_event(struct trace_uprobe *tu)
 	return ret;
 }
 
-static void unregister_uprobe_event(struct trace_uprobe *tu)
+static int unregister_uprobe_event(struct trace_uprobe *tu)
 {
+	int ret;
+
 	/* tu->event is unregistered in trace_remove_event_call() */
-	trace_remove_event_call(&tu->call);
+	ret = trace_remove_event_call(&tu->call);
+	if (ret)
+		return ret;
 	kfree(tu->call.print_fmt);
 	tu->call.print_fmt = NULL;
+	return 0;
 }
 
 /* Make a trace interface for controling probe points */
-- 
1.7.10.4

Re: [PATCH v2 0/1] tracing: trace_remove_event_call() should fail if call/file is in use

[Steven Rostedt]

On Wed, 2013-07-31 at 19:38 +0200, Oleg Nesterov wrote:
> On 07/31, Steven Rostedt wrote:
> >
> > On Mon, 2013-07-29 at 19:50 +0200, Oleg Nesterov wrote:
> > >
> > > Now we are ready to change trace_kprobe.c and trace_uprobe.c, Steven
> > > already has the patches.
> >
> > Can you refresh my memory. My INBOX is quite full. What were the
> > subjects for these patches?
> 
> Please see the attached mbox. And notice who is the author ;)

Heh, who is that guy?

> I also added the ack from Masami.

Thanks, but I'll take in from the email as that's how my scripts work (I
cc'd myself)

-- Steve

> 
> But if you only need the subjects:
> 
> 	[RFC][PATCH 3/4] tracing/kprobes: Fail to unregister if probe event files are open
> 	[RFC][PATCH 4/4] tracing/uprobes: Fail to unregister if probe event files are open
> 
> Oleg.