[PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[Song Liu]

As Miklos reported and suggested:

  This pattern repeats two times in trace_uprobe.c and in
  kernel/events/core.c as well:

      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
      if (ret)
          goto fail_address_parse;

      inode = igrab(d_inode(path.dentry));
      path_put(&path);

  And it's wrong.  You can only hold a reference to the inode if you
  have an active ref to the superblock as well (which is normally
  through path.mnt) or holding s_umount.

  This way unmounting the containing filesystem while the tracepoint is
  active will give you the "VFS: Busy inodes after unmount..." message
  and a crash when the inode is finally put.

  Solution: store path instead of inode.

This patch fixes two instances in trace_uprobe.c.

Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Howard McLauchlan <hmclauchlan@fb.com>
Cc: Josef Bacik <jbacik@fb.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Song Liu <songliubraving@fb.com>
---
 kernel/trace/trace_uprobe.c | 42 ++++++++++++++----------------------------
 1 file changed, 14 insertions(+), 28 deletions(-)

diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
index 0d450b4..80dfcdf 100644
--- a/kernel/trace/trace_uprobe.c
+++ b/kernel/trace/trace_uprobe.c
@@ -55,7 +55,7 @@ struct trace_uprobe {
 	struct list_head		list;
 	struct trace_uprobe_filter	filter;
 	struct uprobe_consumer		consumer;
-	struct inode			*inode;
+	struct path			path;
 	char				*filename;
 	unsigned long			offset;
 	unsigned long			nhit;
@@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
 	for (i = 0; i < tu->tp.nr_args; i++)
 		traceprobe_free_probe_arg(&tu->tp.args[i]);
 
-	iput(tu->inode);
+	path_put(&tu->path);
 	kfree(tu->tp.call.class->system);
 	kfree(tu->tp.call.name);
 	kfree(tu->filename);
@@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
 static int create_trace_uprobe(int argc, char **argv)
 {
 	struct trace_uprobe *tu;
-	struct inode *inode;
 	char *arg, *event, *group, *filename;
 	char buf[MAX_EVENT_NAME_LEN];
 	struct path path;
@@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
 	bool is_delete, is_return;
 	int i, ret;
 
-	inode = NULL;
 	ret = 0;
 	is_delete = false;
 	is_return = false;
@@ -448,14 +446,6 @@ static int create_trace_uprobe(int argc, char **argv)
 	if (ret)
 		goto fail_address_parse;
 
-	inode = igrab(d_inode(path.dentry));
-	path_put(&path);
-
-	if (!inode || !S_ISREG(inode->i_mode)) {
-		ret = -EINVAL;
-		goto fail_address_parse;
-	}
-
 	ret = kstrtoul(arg, 0, &offset);
 	if (ret)
 		goto fail_address_parse;
@@ -490,7 +480,8 @@ static int create_trace_uprobe(int argc, char **argv)
 		goto fail_address_parse;
 	}
 	tu->offset = offset;
-	tu->inode = inode;
+	tu->path.mnt = path.mnt;
+	tu->path.dentry = path.dentry;
 	tu->filename = kstrdup(filename, GFP_KERNEL);
 
 	if (!tu->filename) {
@@ -558,7 +549,7 @@ static int create_trace_uprobe(int argc, char **argv)
 	return ret;
 
 fail_address_parse:
-	iput(inode);
+	path_put(&path);
 
 	pr_info("Failed to parse address or file.\n");
 
@@ -937,7 +928,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
 		goto err_flags;
 
 	tu->consumer.filter = filter;
-	ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
+	ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
+			      &tu->consumer);
 	if (ret)
 		goto err_buffer;
 
@@ -981,7 +973,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
 
 	WARN_ON(!uprobe_filter_is_empty(&tu->filter));
 
-	uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
+	uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
 	tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
 
 	uprobe_buffer_disable();
@@ -1056,7 +1048,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
 	write_unlock(&tu->filter.rwlock);
 
 	if (!done)
-		return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
+		return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
+				    &tu->consumer, false);
 
 	return 0;
 }
@@ -1088,7 +1081,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
 
 	err = 0;
 	if (!done) {
-		err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
+		err = uprobe_apply(d_inode(tu->path.dentry),
+				   tu->offset, &tu->consumer, true);
 		if (err)
 			uprobe_perf_close(tu, event);
 	}
@@ -1352,7 +1346,6 @@ struct trace_event_call *
 create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
 {
 	struct trace_uprobe *tu;
-	struct inode *inode;
 	struct path path;
 	int ret;
 
@@ -1360,14 +1353,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
 	if (ret)
 		return ERR_PTR(ret);
 
-	inode = igrab(d_inode(path.dentry));
-	path_put(&path);
-
-	if (!inode || !S_ISREG(inode->i_mode)) {
-		iput(inode);
-		return ERR_PTR(-EINVAL);
-	}
-
 	/*
 	 * local trace_kprobes are not added to probe_list, so they are never
 	 * searched in find_trace_kprobe(). Therefore, there is no concern of
@@ -1383,7 +1368,8 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
 	}
 
 	tu->offset = offs;
-	tu->inode = inode;
+	tu->path.mnt = path.mnt;
+	tu->path.dentry = path.dentry;
 	tu->filename = kstrdup(name, GFP_KERNEL);
 	init_trace_event_call(tu, &tu->tp.call);
 
-- 
2.9.5

[PATCH 2/2] perf/core: fix bad use of igrab in kernel/event/core.c

[Song Liu]

As Miklos reported and suggested:

  This pattern repeats two times in trace_uprobe.c and in
  kernel/events/core.c as well:

      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
      if (ret)
          goto fail_address_parse;

      inode = igrab(d_inode(path.dentry));
      path_put(&path);

  And it's wrong.  You can only hold a reference to the inode if you
  have an active ref to the superblock as well (which is normally
  through path.mnt) or holding s_umount.

  This way unmounting the containing filesystem while the tracepoint is
  active will give you the "VFS: Busy inodes after unmount..." message
  and a crash when the inode is finally put.

  Solution: store path instead of inode.

This patch fixes the issue in kernel/event/core.c.

NOTE: Based on my understanding, perf_addr_filter only supports intel_pt.
However, my test system doesn't support address filtering (or I made a
mistake?). Therefore, I have NOT tested this patch.

Could someone please help test it?

Fixes: 375637bc5249 ("perf/core: Introduce address range filtering")
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Song Liu <songliubraving@fb.com>
---
 arch/x86/events/intel/pt.c |  4 ++--
 include/linux/perf_event.h |  2 +-
 kernel/events/core.c       | 21 +++++++++------------
 3 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 3b99394..8d016ce 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1194,7 +1194,7 @@ static int pt_event_addr_filters_validate(struct list_head *filters)
 		    filter->action == PERF_ADDR_FILTER_ACTION_START)
 			return -EOPNOTSUPP;
 
-		if (!filter->inode) {
+		if (!filter->path.dentry) {
 			if (!valid_kernel_ip(filter->offset))
 				return -EINVAL;
 
@@ -1221,7 +1221,7 @@ static void pt_event_addr_filters_sync(struct perf_event *event)
 		return;
 
 	list_for_each_entry(filter, &head->list, entry) {
-		if (filter->inode && !offs[range]) {
+		if (filter->path.dentry && !offs[range]) {
 			msr_a = msr_b = 0;
 		} else {
 			/* apply the offset */
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index e71e99e..88922d8 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -467,7 +467,7 @@ enum perf_addr_filter_action_t {
  */
 struct perf_addr_filter {
 	struct list_head	entry;
-	struct inode		*inode;
+	struct path		path;
 	unsigned long		offset;
 	unsigned long		size;
 	enum perf_addr_filter_action_t	action;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index d7af828..7d711ed 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6668,7 +6668,7 @@ static void perf_event_addr_filters_exec(struct perf_event *event, void *data)
 
 	raw_spin_lock_irqsave(&ifh->lock, flags);
 	list_for_each_entry(filter, &ifh->list, entry) {
-		if (filter->inode) {
+		if (filter->path.dentry) {
 			event->addr_filters_offs[count] = 0;
 			restart++;
 		}
@@ -7333,7 +7333,7 @@ static bool perf_addr_filter_match(struct perf_addr_filter *filter,
 				     struct file *file, unsigned long offset,
 				     unsigned long size)
 {
-	if (filter->inode != file_inode(file))
+	if (d_inode(filter->path.dentry) != file_inode(file))
 		return false;
 
 	if (filter->offset > offset + size)
@@ -8674,8 +8674,7 @@ static void free_filters_list(struct list_head *filters)
 	struct perf_addr_filter *filter, *iter;
 
 	list_for_each_entry_safe(filter, iter, filters, entry) {
-		if (filter->inode)
-			iput(filter->inode);
+		path_put(&filter->path);
 		list_del(&filter->entry);
 		kfree(filter);
 	}
@@ -8772,7 +8771,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)
 		 * Adjust base offset if the filter is associated to a binary
 		 * that needs to be mapped:
 		 */
-		if (filter->inode)
+		if (filter->path.dentry)
 			event->addr_filters_offs[count] =
 				perf_addr_filter_apply(filter, mm);
 
@@ -8846,7 +8845,6 @@ perf_event_parse_addr_filter(struct perf_event *event, char *fstr,
 {
 	struct perf_addr_filter *filter = NULL;
 	char *start, *orig, *filename = NULL;
-	struct path path;
 	substring_t args[MAX_OPT_ARGS];
 	int state = IF_STATE_ACTION, token;
 	unsigned int kernel = 0;
@@ -8959,19 +8957,18 @@ perf_event_parse_addr_filter(struct perf_event *event, char *fstr,
 					goto fail_free_name;
 
 				/* look up the path and grab its inode */
-				ret = kern_path(filename, LOOKUP_FOLLOW, &path);
+				ret = kern_path(filename, LOOKUP_FOLLOW,
+						&filter->path);
 				if (ret)
 					goto fail_free_name;
 
-				filter->inode = igrab(d_inode(path.dentry));
-				path_put(&path);
 				kfree(filename);
 				filename = NULL;
 
 				ret = -EINVAL;
-				if (!filter->inode ||
-				    !S_ISREG(filter->inode->i_mode))
-					/* free_filters_list() will iput() */
+				if (!filter->path.dentry ||
+				    !S_ISREG(d_inode(filter->path.dentry)
+					     ->i_mode))
 					goto fail;
 
 				event->addr_filters.nr_file_filters++;
-- 
2.9.5

Re: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[Miklos Szeredi]

On Wed, Apr 18, 2018 at 8:29 AM, Song Liu <songliubraving@fb.com> wrote:
> As Miklos reported and suggested:
>
>   This pattern repeats two times in trace_uprobe.c and in
>   kernel/events/core.c as well:
>
>       ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>       if (ret)
>           goto fail_address_parse;
>
>       inode = igrab(d_inode(path.dentry));
>       path_put(&path);
>
>   And it's wrong.  You can only hold a reference to the inode if you
>   have an active ref to the superblock as well (which is normally
>   through path.mnt) or holding s_umount.
>
>   This way unmounting the containing filesystem while the tracepoint is
>   active will give you the "VFS: Busy inodes after unmount..." message
>   and a crash when the inode is finally put.
>
>   Solution: store path instead of inode.
>
> This patch fixes two instances in trace_uprobe.c.
>
> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
> Cc: Steven Rostedt <rostedt@goodmis.org>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Howard McLauchlan <hmclauchlan@fb.com>
> Cc: Josef Bacik <jbacik@fb.com>
> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> Reported-by: Miklos Szeredi <miklos@szeredi.hu>
> Signed-off-by: Song Liu <songliubraving@fb.com>
> ---
>  kernel/trace/trace_uprobe.c | 42 ++++++++++++++----------------------------
>  1 file changed, 14 insertions(+), 28 deletions(-)
>
> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
> index 0d450b4..80dfcdf 100644
> --- a/kernel/trace/trace_uprobe.c
> +++ b/kernel/trace/trace_uprobe.c
> @@ -55,7 +55,7 @@ struct trace_uprobe {
>         struct list_head                list;
>         struct trace_uprobe_filter      filter;
>         struct uprobe_consumer          consumer;
> -       struct inode                    *inode;
> +       struct path                     path;
>         char                            *filename;
>         unsigned long                   offset;
>         unsigned long                   nhit;
> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
>         for (i = 0; i < tu->tp.nr_args; i++)
>                 traceprobe_free_probe_arg(&tu->tp.args[i]);
>
> -       iput(tu->inode);
> +       path_put(&tu->path);
>         kfree(tu->tp.call.class->system);
>         kfree(tu->tp.call.name);
>         kfree(tu->filename);
> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
>  static int create_trace_uprobe(int argc, char **argv)
>  {
>         struct trace_uprobe *tu;
> -       struct inode *inode;
>         char *arg, *event, *group, *filename;
>         char buf[MAX_EVENT_NAME_LEN];
>         struct path path;
> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
>         bool is_delete, is_return;
>         int i, ret;
>
> -       inode = NULL;
>         ret = 0;
>         is_delete = false;
>         is_return = false;
> @@ -448,14 +446,6 @@ static int create_trace_uprobe(int argc, char **argv)
>         if (ret)
>                 goto fail_address_parse;
>
> -       inode = igrab(d_inode(path.dentry));

This is not against -linus tree.

> -       path_put(&path);
> -
> -       if (!inode || !S_ISREG(inode->i_mode)) {
> -               ret = -EINVAL;
> -               goto fail_address_parse;
> -       }
> -
>         ret = kstrtoul(arg, 0, &offset);
>         if (ret)
>                 goto fail_address_parse;
> @@ -490,7 +480,8 @@ static int create_trace_uprobe(int argc, char **argv)
>                 goto fail_address_parse;
>         }
>         tu->offset = offset;
> -       tu->inode = inode;
> +       tu->path.mnt = path.mnt;
> +       tu->path.dentry = path.dentry;

You can just assign the whole structure.  No need to mess with
individual members.

        tu->path = path;

>         tu->filename = kstrdup(filename, GFP_KERNEL);
>
>         if (!tu->filename) {
> @@ -558,7 +549,7 @@ static int create_trace_uprobe(int argc, char **argv)
>         return ret;
>
>  fail_address_parse:
> -       iput(inode);
> +       path_put(&path);
>
>         pr_info("Failed to parse address or file.\n");
>
> @@ -937,7 +928,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>                 goto err_flags;
>
>         tu->consumer.filter = filter;
> -       ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> +       ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
> +                             &tu->consumer);

It is not entirely clear how the lifetime of uprobe relates to the
lifetime of trace_uprobe.  Is the uprobe object never going to survive
its creator trace_uprobe object?

If that's the case, it warrants a comment.  If that's not the case,
then the path would need to be passed to uprobe_resister() which would
need to obtain its own reference.

>         if (ret)
>                 goto err_buffer;
>
> @@ -981,7 +973,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>
>         WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>
> -       uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
> +       uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
>         tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>
>         uprobe_buffer_disable();
> @@ -1056,7 +1048,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>         write_unlock(&tu->filter.rwlock);
>
>         if (!done)
> -               return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
> +               return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
> +                                   &tu->consumer, false);
>
>         return 0;
>  }
> @@ -1088,7 +1081,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>
>         err = 0;
>         if (!done) {
> -               err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
> +               err = uprobe_apply(d_inode(tu->path.dentry),
> +                                  tu->offset, &tu->consumer, true);
>                 if (err)
>                         uprobe_perf_close(tu, event);
>         }
> @@ -1352,7 +1346,6 @@ struct trace_event_call *
>  create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>  {
>         struct trace_uprobe *tu;
> -       struct inode *inode;
>         struct path path;
>         int ret;
>
> @@ -1360,14 +1353,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>         if (ret)
>                 return ERR_PTR(ret);
>
> -       inode = igrab(d_inode(path.dentry));
> -       path_put(&path);
> -
> -       if (!inode || !S_ISREG(inode->i_mode)) {
> -               iput(inode);
> -               return ERR_PTR(-EINVAL);
> -       }
> -
>         /*
>          * local trace_kprobes are not added to probe_list, so they are never
>          * searched in find_trace_kprobe(). Therefore, there is no concern of
> @@ -1383,7 +1368,8 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>         }
>
>         tu->offset = offs;
> -       tu->inode = inode;
> +       tu->path.mnt = path.mnt;
> +       tu->path.dentry = path.dentry;

tu->path = path


>         tu->filename = kstrdup(name, GFP_KERNEL);
>         init_trace_event_call(tu, &tu->tp.call);
>
> --
> 2.9.5
>

Re: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[Steven Rostedt]

On Wed, 18 Apr 2018 16:03:42 +0200
Miklos Szeredi <miklos@szeredi.hu> wrote:

> > @@ -937,7 +928,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
> >                 goto err_flags;
> >
> >         tu->consumer.filter = filter;
> > -       ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
> > +       ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
> > +                             &tu->consumer);  
> 
> It is not entirely clear how the lifetime of uprobe relates to the
> lifetime of trace_uprobe.  Is the uprobe object never going to survive
> its creator trace_uprobe object?

Not exactly sure what you mean here.

The trace_uprobe (the probe event) is created, it doesn't do anything
until it is enabled. This function is called when it is enabled. The
trace_uprobe (probe event) can not be deleted while it is enabled
(EBUSY).

Are you asking what happens if the file is deleted while it has probe?
That I don't know about (haven't tried it out). But I would hope that
it keeps a reference to the inode, isn't that what the igrab is for?
And is now being replaced by a reference on the path, or is that the
problem?

-- Steve


> 
> If that's the case, it warrants a comment.  If that's not the case,
> then the path would need to be passed to uprobe_resister() which would
> need to obtain its own reference.
> 
> >         if (ret)
> >                 goto err_buffer;
> >

Re: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[Miklos Szeredi]

On Wed, Apr 18, 2018 at 4:25 PM, Steven Rostedt <rostedt@goodmis.org> wrote:
> On Wed, 18 Apr 2018 16:03:42 +0200
> Miklos Szeredi <miklos@szeredi.hu> wrote:
>
>> > @@ -937,7 +928,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>> >                 goto err_flags;
>> >
>> >         tu->consumer.filter = filter;
>> > -       ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
>> > +       ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
>> > +                             &tu->consumer);
>>
>> It is not entirely clear how the lifetime of uprobe relates to the
>> lifetime of trace_uprobe.  Is the uprobe object never going to survive
>> its creator trace_uprobe object?
>
> Not exactly sure what you mean here.
>
> The trace_uprobe (the probe event) is created, it doesn't do anything
> until it is enabled. This function is called when it is enabled. The
> trace_uprobe (probe event) can not be deleted while it is enabled
> (EBUSY).
>
> Are you asking what happens if the file is deleted while it has probe?
> That I don't know about (haven't tried it out). But I would hope that
> it keeps a reference to the inode, isn't that what the igrab is for?
> And is now being replaced by a reference on the path, or is that the
> problem?

No, that's not the problem.

What I don't see is how the uprobe object relates to the trace_uprobe object.

Because after the patch the uprobe object still only has a ref to the
inode, and that can lead to the same issue as with trace_uprobe.
OTOH if uprobe can't survive its creating trace_uprobe, then it
doesn't need to take a ref to the inode at all, since trace_uprobe
already holds it.   Taking an extra ref isn't incorrect, it's just
unnecessary and confusing.

So this needs to be cleared up in some way.

Thanks,
Miklos

Re: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[Steven Rostedt]

On Wed, 18 Apr 2018 16:40:19 +0200
Miklos Szeredi <miklos@szeredi.hu> wrote:


> > The trace_uprobe (the probe event) is created, it doesn't do anything
> > until it is enabled. This function is called when it is enabled. The
> > trace_uprobe (probe event) can not be deleted while it is enabled
> > (EBUSY).
> >
> > Are you asking what happens if the file is deleted while it has probe?
> > That I don't know about (haven't tried it out). But I would hope that
> > it keeps a reference to the inode, isn't that what the igrab is for?
> > And is now being replaced by a reference on the path, or is that the
> > problem?  
> 
> No, that's not the problem.
> 
> What I don't see is how the uprobe object relates to the trace_uprobe object.
> 
> Because after the patch the uprobe object still only has a ref to the
> inode, and that can lead to the same issue as with trace_uprobe.
> OTOH if uprobe can't survive its creating trace_uprobe, then it
> doesn't need to take a ref to the inode at all, since trace_uprobe
> already holds it.   Taking an extra ref isn't incorrect, it's just
> unnecessary and confusing.
> 
> So this needs to be cleared up in some way.

The uprobe created by the trace_uprobe creation must be deleted before
the trace_uprobe can be deleted. Basically we have this:

 # cd /sys/kernel/tracing
 # echo "uprobe creation text" > uprobe_events

The trace_uprobe is created (but not the uprobe itself). This is what
calls create_trace_uprobe().

 # echo 1 > events/uprobes/enable

This enables all the trace uprobe events, which creates the uprobes.
This is the action that calls probe_event_enable(), which creates
uprobes.

At this point, any write to uprobe_events that would destroy the trace
uprobes would return with -EBUSY, and the trace uprobes will not be
deleted.

 # echo 0 > events/uprobes/enable

This will call the probe_event_disable() which will call
uprobe_unregister() which will destroy the uprobe.

Now we can delete the trace uprobe.

Does that answer your question? A uprobe created for trace uprobes can
not survive the trace uprobe itself.

-- Steve

Re: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[Song Liu]

> On Apr 18, 2018, at 7:03 AM, Miklos Szeredi <miklos@szeredi.hu> wrote:
> 
> On Wed, Apr 18, 2018 at 8:29 AM, Song Liu <songliubraving@fb.com> wrote:
>> As Miklos reported and suggested:
>> 
>>  This pattern repeats two times in trace_uprobe.c and in
>>  kernel/events/core.c as well:
>> 
>>      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>      if (ret)
>>          goto fail_address_parse;
>> 
>>      inode = igrab(d_inode(path.dentry));
>>      path_put(&path);
>> 
>>  And it's wrong.  You can only hold a reference to the inode if you
>>  have an active ref to the superblock as well (which is normally
>>  through path.mnt) or holding s_umount.
>> 
>>  This way unmounting the containing filesystem while the tracepoint is
>>  active will give you the "VFS: Busy inodes after unmount..." message
>>  and a crash when the inode is finally put.
>> 
>>  Solution: store path instead of inode.
>> 
>> This patch fixes two instances in trace_uprobe.c.
>> 
>> Fixes: f3f096cfedf8 ("tracing: Provide trace events interface for uprobes")
>> Fixes: 33ea4b24277b ("perf/core: Implement the 'perf_uprobe' PMU")
>> Cc: Steven Rostedt <rostedt@goodmis.org>
>> Cc: Ingo Molnar <mingo@redhat.com>
>> Cc: Howard McLauchlan <hmclauchlan@fb.com>
>> Cc: Josef Bacik <jbacik@fb.com>
>> Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
>> Reported-by: Miklos Szeredi <miklos@szeredi.hu>
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>> kernel/trace/trace_uprobe.c | 42 ++++++++++++++----------------------------
>> 1 file changed, 14 insertions(+), 28 deletions(-)
>> 
>> diff --git a/kernel/trace/trace_uprobe.c b/kernel/trace/trace_uprobe.c
>> index 0d450b4..80dfcdf 100644
>> --- a/kernel/trace/trace_uprobe.c
>> +++ b/kernel/trace/trace_uprobe.c
>> @@ -55,7 +55,7 @@ struct trace_uprobe {
>>        struct list_head                list;
>>        struct trace_uprobe_filter      filter;
>>        struct uprobe_consumer          consumer;
>> -       struct inode                    *inode;
>> +       struct path                     path;
>>        char                            *filename;
>>        unsigned long                   offset;
>>        unsigned long                   nhit;
>> @@ -289,7 +289,7 @@ static void free_trace_uprobe(struct trace_uprobe *tu)
>>        for (i = 0; i < tu->tp.nr_args; i++)
>>                traceprobe_free_probe_arg(&tu->tp.args[i]);
>> 
>> -       iput(tu->inode);
>> +       path_put(&tu->path);
>>        kfree(tu->tp.call.class->system);
>>        kfree(tu->tp.call.name);
>>        kfree(tu->filename);
>> @@ -363,7 +363,6 @@ static int register_trace_uprobe(struct trace_uprobe *tu)
>> static int create_trace_uprobe(int argc, char **argv)
>> {
>>        struct trace_uprobe *tu;
>> -       struct inode *inode;
>>        char *arg, *event, *group, *filename;
>>        char buf[MAX_EVENT_NAME_LEN];
>>        struct path path;
>> @@ -371,7 +370,6 @@ static int create_trace_uprobe(int argc, char **argv)
>>        bool is_delete, is_return;
>>        int i, ret;
>> 
>> -       inode = NULL;
>>        ret = 0;
>>        is_delete = false;
>>        is_return = false;
>> @@ -448,14 +446,6 @@ static int create_trace_uprobe(int argc, char **argv)
>>        if (ret)
>>                goto fail_address_parse;
>> 
>> -       inode = igrab(d_inode(path.dentry));
> 
> This is not against -linus tree.

These patches are against tip/perf/core. I can also send version against 
-linus tree. 

> 
>> -       path_put(&path);
>> -
>> -       if (!inode || !S_ISREG(inode->i_mode)) {
>> -               ret = -EINVAL;
>> -               goto fail_address_parse;
>> -       }
>> -
>>        ret = kstrtoul(arg, 0, &offset);
>>        if (ret)
>>                goto fail_address_parse;
>> @@ -490,7 +480,8 @@ static int create_trace_uprobe(int argc, char **argv)
>>                goto fail_address_parse;
>>        }
>>        tu->offset = offset;
>> -       tu->inode = inode;
>> +       tu->path.mnt = path.mnt;
>> +       tu->path.dentry = path.dentry;
> 
> You can just assign the whole structure.  No need to mess with
> individual members.
> 
>        tu->path = path;
Will fix in v2. 
> 
>>        tu->filename = kstrdup(filename, GFP_KERNEL);
>> 
>>        if (!tu->filename) {
>> @@ -558,7 +549,7 @@ static int create_trace_uprobe(int argc, char **argv)
>>        return ret;
>> 
>> fail_address_parse:
>> -       iput(inode);
>> +       path_put(&path);
>> 
>>        pr_info("Failed to parse address or file.\n");
>> 
>> @@ -937,7 +928,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>>                goto err_flags;
>> 
>>        tu->consumer.filter = filter;
>> -       ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
>> +       ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
>> +                             &tu->consumer);
> 
> It is not entirely clear how the lifetime of uprobe relates to the
> lifetime of trace_uprobe.  Is the uprobe object never going to survive
> its creator trace_uprobe object?
> 
> If that's the case, it warrants a comment.  If that's not the case,
> then the path would need to be passed to uprobe_resister() which would
> need to obtain its own reference.

trace_uprobe will not be freed before the uprobe object. trace_uprobe 
holds reference to struct path (with path_get()). 

> 
>>        if (ret)
>>                goto err_buffer;
>> 
>> @@ -981,7 +973,7 @@ probe_event_disable(struct trace_uprobe *tu, struct trace_event_file *file)
>> 
>>        WARN_ON(!uprobe_filter_is_empty(&tu->filter));
>> 
>> -       uprobe_unregister(tu->inode, tu->offset, &tu->consumer);
>> +       uprobe_unregister(d_inode(tu->path.dentry), tu->offset, &tu->consumer);
>>        tu->tp.flags &= file ? ~TP_FLAG_TRACE : ~TP_FLAG_PROFILE;
>> 
>>        uprobe_buffer_disable();
>> @@ -1056,7 +1048,8 @@ static int uprobe_perf_close(struct trace_uprobe *tu, struct perf_event *event)
>>        write_unlock(&tu->filter.rwlock);
>> 
>>        if (!done)
>> -               return uprobe_apply(tu->inode, tu->offset, &tu->consumer, false);
>> +               return uprobe_apply(d_inode(tu->path.dentry), tu->offset,
>> +                                   &tu->consumer, false);
>> 
>>        return 0;
>> }
>> @@ -1088,7 +1081,8 @@ static int uprobe_perf_open(struct trace_uprobe *tu, struct perf_event *event)
>> 
>>        err = 0;
>>        if (!done) {
>> -               err = uprobe_apply(tu->inode, tu->offset, &tu->consumer, true);
>> +               err = uprobe_apply(d_inode(tu->path.dentry),
>> +                                  tu->offset, &tu->consumer, true);
>>                if (err)
>>                        uprobe_perf_close(tu, event);
>>        }
>> @@ -1352,7 +1346,6 @@ struct trace_event_call *
>> create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>> {
>>        struct trace_uprobe *tu;
>> -       struct inode *inode;
>>        struct path path;
>>        int ret;
>> 
>> @@ -1360,14 +1353,6 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>>        if (ret)
>>                return ERR_PTR(ret);
>> 
>> -       inode = igrab(d_inode(path.dentry));
>> -       path_put(&path);
>> -
>> -       if (!inode || !S_ISREG(inode->i_mode)) {
>> -               iput(inode);
>> -               return ERR_PTR(-EINVAL);
>> -       }
>> -
>>        /*
>>         * local trace_kprobes are not added to probe_list, so they are never
>>         * searched in find_trace_kprobe(). Therefore, there is no concern of
>> @@ -1383,7 +1368,8 @@ create_local_trace_uprobe(char *name, unsigned long offs, bool is_return)
>>        }
>> 
>>        tu->offset = offs;
>> -       tu->inode = inode;
>> +       tu->path.mnt = path.mnt;
>> +       tu->path.dentry = path.dentry;
> 
> tu->path = path
> 
> 
>>        tu->filename = kstrdup(name, GFP_KERNEL);
>>        init_trace_event_call(tu, &tu->tp.call);
>> 
>> --
>> 2.9.5
>> 

Re: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[Song Liu]

> On Apr 18, 2018, at 7:25 AM, Steven Rostedt <rostedt@goodmis.org> wrote:
> 
> On Wed, 18 Apr 2018 16:03:42 +0200
> Miklos Szeredi <miklos@szeredi.hu> wrote:
> 
>>> @@ -937,7 +928,8 @@ probe_event_enable(struct trace_uprobe *tu, struct trace_event_file *file,
>>>                goto err_flags;
>>> 
>>>        tu->consumer.filter = filter;
>>> -       ret = uprobe_register(tu->inode, tu->offset, &tu->consumer);
>>> +       ret = uprobe_register(d_inode(tu->path.dentry), tu->offset,
>>> +                             &tu->consumer);  
>> 
>> It is not entirely clear how the lifetime of uprobe relates to the
>> lifetime of trace_uprobe.  Is the uprobe object never going to survive
>> its creator trace_uprobe object?
> 
> Not exactly sure what you mean here.
> 
> The trace_uprobe (the probe event) is created, it doesn't do anything
> until it is enabled. This function is called when it is enabled. The
> trace_uprobe (probe event) can not be deleted while it is enabled
> (EBUSY).
> 
> Are you asking what happens if the file is deleted while it has probe?
> That I don't know about (haven't tried it out). But I would hope that
> it keeps a reference to the inode, isn't that what the igrab is for?
> And is now being replaced by a reference on the path, or is that the
> problem?
> 
> -- Steve
> 

Just as Miklos pointed out, I run tests with the uprobe and confirmed 
that igrab() is not sufficient to prevent umount. When we change it to 
path_get()/path_put(), umount will abort because of the trace_uprobe. 

Song


>> 
>> If that's the case, it warrants a comment.  If that's not the case,
>> then the path would need to be passed to uprobe_resister() which would
>> need to obtain its own reference.
>> 
>>>        if (ret)
>>>                goto err_buffer;
>>> 

Re: [PATCH 1/2] tracing: fix bad use of igrab in trace_uprobe.c

[Steven Rostedt]

On Wed, 18 Apr 2018 16:08:50 +0000
Song Liu <songliubraving@fb.com> wrote:

> > This is not against -linus tree.  
> 
> These patches are against tip/perf/core. I can also send version against 
> -linus tree. 

I can take this patch in my tree (which is currently equal to
4.17-rc1). The other patch should go through tip.

-- Steve

Re: [PATCH 2/2] perf/core: fix bad use of igrab in kernel/event/core.c

[Alexander Shishkin]

On Tue, Apr 17, 2018 at 11:29:07PM -0700, Song Liu wrote:
> As Miklos reported and suggested:
> 
>   This pattern repeats two times in trace_uprobe.c and in
>   kernel/events/core.c as well:
> 
>       ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>       if (ret)
>           goto fail_address_parse;
> 
>       inode = igrab(d_inode(path.dentry));
>       path_put(&path);
> 
>   And it's wrong.  You can only hold a reference to the inode if you
>   have an active ref to the superblock as well (which is normally
>   through path.mnt) or holding s_umount.

Oops. I must have snatched it from the uprobe code without thinking.

>   This way unmounting the containing filesystem while the tracepoint is
>   active will give you the "VFS: Busy inodes after unmount..." message
>   and a crash when the inode is finally put.
> 
>   Solution: store path instead of inode.
> 
> This patch fixes the issue in kernel/event/core.c.
> 
> NOTE: Based on my understanding, perf_addr_filter only supports intel_pt.

Coresight too, but that's probably even further away from what you have.

> However, my test system doesn't support address filtering (or I made a
> mistake?). Therefore, I have NOT tested this patch.

Check /sys/devices/intel_pt/caps/num_address_ranges, if it's non-zero,
it's supported.

> Could someone please help test it?

Yes:

Reviewed-and-tested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>

The subject line needs a little love to be more like other perf commits, but
other than that, looks good.

Thanks!

Re: [PATCH 2/2] perf/core: fix bad use of igrab in kernel/event/core.c

[Song Liu]

> On Apr 18, 2018, at 11:17 PM, Alexander Shishkin <alexander.shishkin@linux.intel.com> wrote:
> 
> On Tue, Apr 17, 2018 at 11:29:07PM -0700, Song Liu wrote:
>> As Miklos reported and suggested:
>> 
>>  This pattern repeats two times in trace_uprobe.c and in
>>  kernel/events/core.c as well:
>> 
>>      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
>>      if (ret)
>>          goto fail_address_parse;
>> 
>>      inode = igrab(d_inode(path.dentry));
>>      path_put(&path);
>> 
>>  And it's wrong.  You can only hold a reference to the inode if you
>>  have an active ref to the superblock as well (which is normally
>>  through path.mnt) or holding s_umount.
> 
> Oops. I must have snatched it from the uprobe code without thinking.
> 
>>  This way unmounting the containing filesystem while the tracepoint is
>>  active will give you the "VFS: Busy inodes after unmount..." message
>>  and a crash when the inode is finally put.
>> 
>>  Solution: store path instead of inode.
>> 
>> This patch fixes the issue in kernel/event/core.c.
>> 
>> NOTE: Based on my understanding, perf_addr_filter only supports intel_pt.
> 
> Coresight too, but that's probably even further away from what you have.
> 
>> However, my test system doesn't support address filtering (or I made a
>> mistake?). Therefore, I have NOT tested this patch.
> 
> Check /sys/devices/intel_pt/caps/num_address_ranges, if it's non-zero,
> it's supported.
> 
>> Could someone please help test it?
> 
> Yes:
> 
> Reviewed-and-tested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
> 
> The subject line needs a little love to be more like other perf commits, but
> other than that, looks good.
> 
> Thanks!

Did this patch ever make into tip/perf/XX trees? If not, what shall I do 
to move it ahead?

Thanks,
Song

Re: [PATCH 2/2] perf/core: fix bad use of igrab in kernel/event/core.c

[Peter Zijlstra]

On Tue, May 22, 2018 at 09:56:18PM +0000, Song Liu wrote:
> Did this patch ever make into tip/perf/XX trees? If not, what shall I do 
> to move it ahead?

Got it now, thanks for the reminder.

[tip:perf/core] perf/core: Fix bad use of igrab()

[tip-bot for Song Liu]

Commit-ID:  9511bce9fe8e5e6c0f923c09243a713eba560141
Gitweb:     https://git.kernel.org/tip/9511bce9fe8e5e6c0f923c09243a713eba560141
Author:     Song Liu <songliubraving@fb.com>
AuthorDate: Tue, 17 Apr 2018 23:29:07 -0700
Committer:  Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 25 May 2018 08:11:10 +0200

perf/core: Fix bad use of igrab()

As Miklos reported and suggested:

 "This pattern repeats two times in trace_uprobe.c and in
  kernel/events/core.c as well:

      ret = kern_path(filename, LOOKUP_FOLLOW, &path);
      if (ret)
          goto fail_address_parse;

      inode = igrab(d_inode(path.dentry));
      path_put(&path);

  And it's wrong.  You can only hold a reference to the inode if you
  have an active ref to the superblock as well (which is normally
  through path.mnt) or holding s_umount.

  This way unmounting the containing filesystem while the tracepoint is
  active will give you the "VFS: Busy inodes after unmount..." message
  and a crash when the inode is finally put.

  Solution: store path instead of inode."

This patch fixes the issue in kernel/event/core.c.

Reviewed-and-tested-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reported-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <kernel-team@fb.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 375637bc5249 ("perf/core: Introduce address range filtering")
Link: http://lkml.kernel.org/r/20180418062907.3210386-2-songliubraving@fb.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
 arch/x86/events/intel/pt.c |  4 ++--
 include/linux/perf_event.h |  2 +-
 kernel/events/core.c       | 21 +++++++++------------
 3 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/arch/x86/events/intel/pt.c b/arch/x86/events/intel/pt.c
index 3b993942a0e4..8d016ce5b80d 100644
--- a/arch/x86/events/intel/pt.c
+++ b/arch/x86/events/intel/pt.c
@@ -1194,7 +1194,7 @@ static int pt_event_addr_filters_validate(struct list_head *filters)
 		    filter->action == PERF_ADDR_FILTER_ACTION_START)
 			return -EOPNOTSUPP;
 
-		if (!filter->inode) {
+		if (!filter->path.dentry) {
 			if (!valid_kernel_ip(filter->offset))
 				return -EINVAL;
 
@@ -1221,7 +1221,7 @@ static void pt_event_addr_filters_sync(struct perf_event *event)
 		return;
 
 	list_for_each_entry(filter, &head->list, entry) {
-		if (filter->inode && !offs[range]) {
+		if (filter->path.dentry && !offs[range]) {
 			msr_a = msr_b = 0;
 		} else {
 			/* apply the offset */
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index def866f7269b..bea0b0cd4bf7 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -467,7 +467,7 @@ enum perf_addr_filter_action_t {
  */
 struct perf_addr_filter {
 	struct list_head	entry;
-	struct inode		*inode;
+	struct path		path;
 	unsigned long		offset;
 	unsigned long		size;
 	enum perf_addr_filter_action_t	action;
diff --git a/kernel/events/core.c b/kernel/events/core.c
index ce6aa5ff3c96..24dea13a27ed 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -6668,7 +6668,7 @@ static void perf_event_addr_filters_exec(struct perf_event *event, void *data)
 
 	raw_spin_lock_irqsave(&ifh->lock, flags);
 	list_for_each_entry(filter, &ifh->list, entry) {
-		if (filter->inode) {
+		if (filter->path.dentry) {
 			event->addr_filters_offs[count] = 0;
 			restart++;
 		}
@@ -7333,7 +7333,7 @@ static bool perf_addr_filter_match(struct perf_addr_filter *filter,
 				     struct file *file, unsigned long offset,
 				     unsigned long size)
 {
-	if (filter->inode != file_inode(file))
+	if (d_inode(filter->path.dentry) != file_inode(file))
 		return false;
 
 	if (filter->offset > offset + size)
@@ -8686,8 +8686,7 @@ static void free_filters_list(struct list_head *filters)
 	struct perf_addr_filter *filter, *iter;
 
 	list_for_each_entry_safe(filter, iter, filters, entry) {
-		if (filter->inode)
-			iput(filter->inode);
+		path_put(&filter->path);
 		list_del(&filter->entry);
 		kfree(filter);
 	}
@@ -8784,7 +8783,7 @@ static void perf_event_addr_filters_apply(struct perf_event *event)
 		 * Adjust base offset if the filter is associated to a binary
 		 * that needs to be mapped:
 		 */
-		if (filter->inode)
+		if (filter->path.dentry)
 			event->addr_filters_offs[count] =
 				perf_addr_filter_apply(filter, mm);
 
@@ -8858,7 +8857,6 @@ perf_event_parse_addr_filter(struct perf_event *event, char *fstr,
 {
 	struct perf_addr_filter *filter = NULL;
 	char *start, *orig, *filename = NULL;
-	struct path path;
 	substring_t args[MAX_OPT_ARGS];
 	int state = IF_STATE_ACTION, token;
 	unsigned int kernel = 0;
@@ -8971,19 +8969,18 @@ perf_event_parse_addr_filter(struct perf_event *event, char *fstr,
 					goto fail_free_name;
 
 				/* look up the path and grab its inode */
-				ret = kern_path(filename, LOOKUP_FOLLOW, &path);
+				ret = kern_path(filename, LOOKUP_FOLLOW,
+						&filter->path);
 				if (ret)
 					goto fail_free_name;
 
-				filter->inode = igrab(d_inode(path.dentry));
-				path_put(&path);
 				kfree(filename);
 				filename = NULL;
 
 				ret = -EINVAL;
-				if (!filter->inode ||
-				    !S_ISREG(filter->inode->i_mode))
-					/* free_filters_list() will iput() */
+				if (!filter->path.dentry ||
+				    !S_ISREG(d_inode(filter->path.dentry)
+					     ->i_mode))
 					goto fail;
 
 				event->addr_filters.nr_file_filters++;