[PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Jiri Olsa]

If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
with read&write permissions, the previous setup will be removed.

Tested with following program:

[snip]
#include <stdio.h>
#include <string.h>

int main(int argc, char **argv)
{
	FILE *f;
	char *mode = "w+";
	char *file = argv[1];

	if (argc == 3)
		mode = argv[2];

	if (NULL == (f = fopen(file, mode))) {
		perror("fopen failed");
		return -1;
	}

	while(!feof(f)) {
#define BUFLEN 100
		char buf[BUFLEN];
		memset(buf, 0, BUFLEN);
		fgets(buf, BUFLEN, f);
		printf(buf);
	}

	fclose(f);
	return 0;
}
[snip]

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>

---
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4521c77..11394bc 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1661,10 +1661,6 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
 		return -ENOMEM;
 
 	mutex_lock(&ftrace_regex_lock);
-	if ((file->f_mode & FMODE_WRITE) &&
-	    !(file->f_flags & O_APPEND))
-		ftrace_filter_reset(enable);
-
 	if (file->f_mode & FMODE_READ) {
 		iter->pg = ftrace_pages_start;
 		iter->flags = enable ? FTRACE_ITER_FILTER :
@@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 		return 0;
 
 	mutex_lock(&ftrace_regex_lock);
+	if ((file->f_mode & FMODE_WRITE) &&
+	    !(file->f_flags & O_APPEND))
+		ftrace_filter_reset(enable);
 
 	if (file->f_mode & FMODE_READ) {
 		struct seq_file *m = file->private_data;

Re: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Li Zefan]

Jiri Olsa wrote:
> If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> with read&write permissions, the previous setup will be removed.
> 

Currently:

 # echo 'sys_open sys_close' > set_ftrace_filter
 # cat set_ftrace_filter
 sys_open
 sys_close

After your patch:

 # echo 'sys_open sys_close' > set_ftrace_filter
 # cat set_ftrace_filter
 sys_close

> Tested with following program:
...
> 
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> 
> ---
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 4521c77..11394bc 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1661,10 +1661,6 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
>  		return -ENOMEM;
>  
>  	mutex_lock(&ftrace_regex_lock);
> -	if ((file->f_mode & FMODE_WRITE) &&
> -	    !(file->f_flags & O_APPEND))
> -		ftrace_filter_reset(enable);
> -
>  	if (file->f_mode & FMODE_READ) {
>  		iter->pg = ftrace_pages_start;
>  		iter->flags = enable ? FTRACE_ITER_FILTER :
> @@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
>  		return 0;
>  
>  	mutex_lock(&ftrace_regex_lock);
> +	if ((file->f_mode & FMODE_WRITE) &&
> +	    !(file->f_flags & O_APPEND))
> +		ftrace_filter_reset(enable);
>  
>  	if (file->f_mode & FMODE_READ) {
>  		struct seq_file *m = file->private_data;
> --

Re: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Jiri Olsa]

On Fri, Jul 17, 2009 at 05:37:24PM +0800, Li Zefan wrote:
> Jiri Olsa wrote:
> > If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> > with read&write permissions, the previous setup will be removed.
> > 
> 
> Currently:
> 
>  # echo 'sys_open sys_close' > set_ftrace_filter
>  # cat set_ftrace_filter
>  sys_open
>  sys_close
> 
> After your patch:
> 
>  # echo 'sys_open sys_close' > set_ftrace_filter
>  # cat set_ftrace_filter
>  sys_close
> 

oops, sry I missed this..

Following patch adds new FTRACE_ITER_RESET flag, as the decision needs
to be taken in "open" and applied in "write".  I'm not sure whats the
policy for adding new flags, but it looks ok to me.

wbr,
jirka


Signed-off-by: Jiri Olsa <jolsa@redhat.com>

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 4521c77..29c4b67 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1364,6 +1364,7 @@ enum {
 	FTRACE_ITER_FAILURES	= (1 << 3),
 	FTRACE_ITER_PRINTALL	= (1 << 4),
 	FTRACE_ITER_HASH	= (1 << 5),
+	FTRACE_ITER_RESET	= (1 << 6),
 };
 
 #define FTRACE_BUFF_MAX (KSYM_SYMBOL_LEN+4) /* room for wildcards */
@@ -1663,11 +1664,11 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
 	mutex_lock(&ftrace_regex_lock);
 	if ((file->f_mode & FMODE_WRITE) &&
 	    !(file->f_flags & O_APPEND))
-		ftrace_filter_reset(enable);
+		iter->flags |= FTRACE_ITER_RESET;
 
 	if (file->f_mode & FMODE_READ) {
 		iter->pg = ftrace_pages_start;
-		iter->flags = enable ? FTRACE_ITER_FILTER :
+		iter->flags |= enable ? FTRACE_ITER_FILTER :
 			FTRACE_ITER_NOTRACE;
 
 		ret = seq_open(file, &show_ftrace_seq_ops);
@@ -2267,6 +2268,11 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 	} else
 		iter = file->private_data;
 
+	if (iter->flags & FTRACE_ITER_RESET) {
+		ftrace_filter_reset(enable);
+		iter->flags &= ~FTRACE_ITER_RESET;
+	}
+
 	if (!*ppos) {
 		iter->flags &= ~FTRACE_ITER_CONT;
 		iter->buffer_idx = 0;

Re: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Li Zefan]

Jiri Olsa wrote:
> On Fri, Jul 17, 2009 at 05:37:24PM +0800, Li Zefan wrote:
>> Jiri Olsa wrote:
>>> If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
>>> with read&write permissions, the previous setup will be removed.
>>>
>> Currently:
>>
>>  # echo 'sys_open sys_close' > set_ftrace_filter
>>  # cat set_ftrace_filter
>>  sys_open
>>  sys_close
>>
>> After your patch:
>>
>>  # echo 'sys_open sys_close' > set_ftrace_filter
>>  # cat set_ftrace_filter
>>  sys_close
>>
> 
> oops, sry I missed this..
> 
> Following patch adds new FTRACE_ITER_RESET flag, as the decision needs
> to be taken in "open" and applied in "write".  I'm not sure whats the
> policy for adding new flags, but it looks ok to me.
> 

I have no strong opinion whether to do the reset in "open" or in first
"write".

All said, I think this is cleaner, without introducing a new flag:

@@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 		return 0;
 
 	mutex_lock(&ftrace_regex_lock);
+	if (file->f_pos == 0 &&
+	    (file->f_mode & FMODE_WRITE) && !(file->f_flags & O_APPEND))
+		ftrace_filter_reset(enable);
 
 	if (file->f_mode & FMODE_READ) {
 		struct seq_file *m = file->private_data;

Re: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Frederic Weisbecker]

On Mon, Jul 20, 2009 at 08:55:54AM +0800, Li Zefan wrote:
> Jiri Olsa wrote:
> > On Fri, Jul 17, 2009 at 05:37:24PM +0800, Li Zefan wrote:
> >> Jiri Olsa wrote:
> >>> If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> >>> with read&write permissions, the previous setup will be removed.
> >>>
> >> Currently:
> >>
> >>  # echo 'sys_open sys_close' > set_ftrace_filter
> >>  # cat set_ftrace_filter
> >>  sys_open
> >>  sys_close
> >>
> >> After your patch:
> >>
> >>  # echo 'sys_open sys_close' > set_ftrace_filter
> >>  # cat set_ftrace_filter
> >>  sys_close
> >>
> > 
> > oops, sry I missed this..
> > 
> > Following patch adds new FTRACE_ITER_RESET flag, as the decision needs
> > to be taken in "open" and applied in "write".  I'm not sure whats the
> > policy for adding new flags, but it looks ok to me.
> > 
> 
> I have no strong opinion whether to do the reset in "open" or in first
> "write".
> 
> All said, I think this is cleaner, without introducing a new flag:
> 
> @@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
>  		return 0;
>  
>  	mutex_lock(&ftrace_regex_lock);
> +	if (file->f_pos == 0 &&
> +	    (file->f_mode & FMODE_WRITE) && !(file->f_flags & O_APPEND))
> +		ftrace_filter_reset(enable);
>  
>  	if (file->f_mode & FMODE_READ) {
>  		struct seq_file *m = file->private_data;


Yeah, that avoids this need of creating a new flag.
Looks like a good solution.

Re: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Jiri Olsa]

On Sun, Jul 19, 2009 at 09:32:25PM -0400, Frederic Weisbecker wrote:
> On Mon, Jul 20, 2009 at 08:55:54AM +0800, Li Zefan wrote:
> > Jiri Olsa wrote:
> > > On Fri, Jul 17, 2009 at 05:37:24PM +0800, Li Zefan wrote:
> > >> Jiri Olsa wrote:
> > >>> If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> > >>> with read&write permissions, the previous setup will be removed.
> > >>>
> > >> Currently:
> > >>
> > >>  # echo 'sys_open sys_close' > set_ftrace_filter
> > >>  # cat set_ftrace_filter
> > >>  sys_open
> > >>  sys_close
> > >>
> > >> After your patch:
> > >>
> > >>  # echo 'sys_open sys_close' > set_ftrace_filter
> > >>  # cat set_ftrace_filter
> > >>  sys_close
> > >>
> > > 
> > > oops, sry I missed this..
> > > 
> > > Following patch adds new FTRACE_ITER_RESET flag, as the decision needs
> > > to be taken in "open" and applied in "write".  I'm not sure whats the
> > > policy for adding new flags, but it looks ok to me.
> > > 
> > 
> > I have no strong opinion whether to do the reset in "open" or in first
> > "write".
> > 
> > All said, I think this is cleaner, without introducing a new flag:
> > 
> > @@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
> >  		return 0;
> >  
> >  	mutex_lock(&ftrace_regex_lock);
> > +	if (file->f_pos == 0 &&
> > +	    (file->f_mode & FMODE_WRITE) && !(file->f_flags & O_APPEND))
> > +		ftrace_filter_reset(enable);
> >  
> >  	if (file->f_mode & FMODE_READ) {
> >  		struct seq_file *m = file->private_data;
> 
> 
> Yeah, that avoids this need of creating a new flag.
> Looks like a good solution.
> 

yes, but this wont work unless the *ppos value is updated instead of the
file->f_pos, because of:


  SYSCALL_DEFINE3(write, unsigned int, fd, const char __user *, buf,
                size_t, count)
  {
	[snip]
                loff_t pos = file_pos_read(file);
                ret = vfs_write(file, buf, count, &pos);
                file_pos_write(file, pos);
	[snip]


Together with this fix I included fix for FTRACE_ITER_CONT flag, since
it does not seem to work correctly.
As far as I understand the reason for FTRACE_ITER_CONT flag is when
there's one regexp. in more write calls. I made a program to test it.

[snip]
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>

int main(int argc, char **argv)
{
        int fd, i;
        char *file = argv[1];

        if (-1 == (fd = open(file, O_WRONLY))) {
                perror("open failed");
                return -1;
        }

        for(i = 0; i < (argc - 2); i++) {
                int len = strlen(argv[2+i]);
                int cnt, off = 0;

                while(len) {
                        cnt = write(fd, argv[2+i] + off, len);
                        len -= cnt;
                        off += cnt;
                }
        }

        close(fd);
        return 0;
}
[snip]

I got following behaviour on the current tip master:

sh-4.0# /tst ./set_ftrace_filter sys_o "pen "
sh-4.0# cat ./set_ftrace_filter 
#### all functions enabled ####


wbr,
jirka

---
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 24e3ff5..041a327 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -1616,10 +1616,6 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
 		return -ENOMEM;
 
 	mutex_lock(&ftrace_regex_lock);
-	if ((file->f_mode & FMODE_WRITE) &&
-	    !(file->f_flags & O_APPEND))
-		ftrace_filter_reset(enable);
-
 	if (file->f_mode & FMODE_READ) {
 		iter->pg = ftrace_pages_start;
 		iter->flags = enable ? FTRACE_ITER_FILTER :
@@ -2225,6 +2221,10 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 	if (!*ppos) {
 		iter->flags &= ~FTRACE_ITER_CONT;
 		iter->buffer_idx = 0;
+
+		if ((file->f_mode & FMODE_WRITE) &&
+		    !(file->f_flags & O_APPEND))
+			ftrace_filter_reset(enable);
 	}
 
 	ret = get_user(ch, ubuf++);
@@ -2233,7 +2233,11 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 	read++;
 	cnt--;
 
-	if (!(iter->flags & ~FTRACE_ITER_CONT)) {
+	/*
+	 * If the parses havent finished with the last write,
+	 * continue reading the user input without skipping spaces.
+	 */
+	if (!(iter->flags & FTRACE_ITER_CONT)) {
 		/* skip white space */
 		while (cnt && isspace(ch)) {
 			ret = get_user(ch, ubuf++);
@@ -2243,8 +2247,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 			cnt--;
 		}
 
+		/* only spaces were written */
 		if (isspace(ch)) {
-			file->f_pos += read;
+			*ppos += read;
 			ret = read;
 			goto out;
 		}
@@ -2273,12 +2278,12 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
 		if (ret)
 			goto out;
 		iter->buffer_idx = 0;
-	} else
+	} else {
 		iter->flags |= FTRACE_ITER_CONT;
+		iter->buffer[iter->buffer_idx++] = ch;
+	}
 
-
-	file->f_pos += read;
-
+	*ppos += read;
 	ret = read;
  out:
 	mutex_unlock(&ftrace_regex_lock);

Re: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Steven Rostedt]

On Thu, 16 Jul 2009, Jiri Olsa wrote:

> If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> with read&write permissions, the previous setup will be removed.

This is exactly what it was suppose to do.

man fopen:

       w+     Open for reading and writing.  The file is created  if  it  does
              not  exist, otherwise it is truncated.  The stream is positioned
              at the beginning of the file.

Which means that if you open a file for "w+" it will truncate it. Hence, 
you will remove all previous settings.

What you want is:

       a+     Open for reading and appending (writing at end  of  file).   The
              file is created if it does not exist.  The initial file position
              for reading is at the beginning  of  the  file,  but  output  is
              always appended to the end of the file.

Change the belowe code from "w+" to "a+" and you get your expected result.

Thus, the current code is correct.

-- Steve



> 
> Tested with following program:
> 
> [snip]
> #include <stdio.h>
> #include <string.h>
> 
> int main(int argc, char **argv)
> {
> 	FILE *f;
> 	char *mode = "w+";
> 	char *file = argv[1];
> 
> 	if (argc == 3)
> 		mode = argv[2];
> 
> 	if (NULL == (f = fopen(file, mode))) {
> 		perror("fopen failed");
> 		return -1;
> 	}
> 
> 	while(!feof(f)) {
> #define BUFLEN 100
> 		char buf[BUFLEN];
> 		memset(buf, 0, BUFLEN);
> 		fgets(buf, BUFLEN, f);
> 		printf(buf);
> 	}
> 
> 	fclose(f);
> 	return 0;
> }
> [snip]
> 
> wbr,
> jirka
> 
> 
> Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> 
> ---
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 4521c77..11394bc 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -1661,10 +1661,6 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
>  		return -ENOMEM;
>  
>  	mutex_lock(&ftrace_regex_lock);
> -	if ((file->f_mode & FMODE_WRITE) &&
> -	    !(file->f_flags & O_APPEND))
> -		ftrace_filter_reset(enable);
> -
>  	if (file->f_mode & FMODE_READ) {
>  		iter->pg = ftrace_pages_start;
>  		iter->flags = enable ? FTRACE_ITER_FILTER :
> @@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
>  		return 0;
>  
>  	mutex_lock(&ftrace_regex_lock);
> +	if ((file->f_mode & FMODE_WRITE) &&
> +	    !(file->f_flags & O_APPEND))
> +		ftrace_filter_reset(enable);
>  
>  	if (file->f_mode & FMODE_READ) {
>  		struct seq_file *m = file->private_data;
> 

Re: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Jiri Olsa]

On Mon, Jul 20, 2009 at 09:11:34PM -0400, Steven Rostedt wrote:
> 
> On Thu, 16 Jul 2009, Jiri Olsa wrote:
> 
> > If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> > with read&write permissions, the previous setup will be removed.
> 
> This is exactly what it was suppose to do.
> 
> man fopen:
> 
>        w+     Open for reading and writing.  The file is created  if  it  does
>               not  exist, otherwise it is truncated.  The stream is positioned
>               at the beginning of the file.
> 
> Which means that if you open a file for "w+" it will truncate it. Hence, 
> you will remove all previous settings.
> 
> What you want is:
> 
>        a+     Open for reading and appending (writing at end  of  file).   The
>               file is created if it does not exist.  The initial file position
>               for reading is at the beginning  of  the  file,  but  output  is
>               always appended to the end of the file.
> 
> Change the belowe code from "w+" to "a+" and you get your expected result.

My point was that if you open set_ftrace_filter/set_ftrace_notrace with just O_RDWR
perm. and will use the file just for reading, the filter will reset.

You're right about the "w+", there's the O_CREAT|O_TRUNC, sry I missed that.. ;)
Anyway with "r+" you'll get O_RDWR perm. only, showing the issue:


sh-4.0# echo "sys_open sys_write" > ./set_ftrace_filter 
sh-4.0# cat ./set_ftrace_filter 
sys_open
sys_write
sh-4.0# /ft ./set_ftrace_filter r+
#### all functions enabled ####
sh-4.0# cat ./set_ftrace_filter 
#### all functions enabled ####
sh-4.0# 


wbr,
jirka

> 
> Thus, the current code is correct.
> 
> -- Steve
> 
> 
> 
> > 
> > Tested with following program:
> > 
> > [snip]
> > #include <stdio.h>
> > #include <string.h>
> > 
> > int main(int argc, char **argv)
> > {
> > 	FILE *f;
> > 	char *mode = "w+";
> > 	char *file = argv[1];
> > 
> > 	if (argc == 3)
> > 		mode = argv[2];
> > 
> > 	if (NULL == (f = fopen(file, mode))) {
> > 		perror("fopen failed");
> > 		return -1;
> > 	}
> > 
> > 	while(!feof(f)) {
> > #define BUFLEN 100
> > 		char buf[BUFLEN];
> > 		memset(buf, 0, BUFLEN);
> > 		fgets(buf, BUFLEN, f);
> > 		printf(buf);
> > 	}
> > 
> > 	fclose(f);
> > 	return 0;
> > }
> > [snip]
> > 
> > wbr,
> > jirka
> > 
> > 
> > Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> > 
> > ---
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 4521c77..11394bc 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -1661,10 +1661,6 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
> >  		return -ENOMEM;
> >  
> >  	mutex_lock(&ftrace_regex_lock);
> > -	if ((file->f_mode & FMODE_WRITE) &&
> > -	    !(file->f_flags & O_APPEND))
> > -		ftrace_filter_reset(enable);
> > -
> >  	if (file->f_mode & FMODE_READ) {
> >  		iter->pg = ftrace_pages_start;
> >  		iter->flags = enable ? FTRACE_ITER_FILTER :
> > @@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
> >  		return 0;
> >  
> >  	mutex_lock(&ftrace_regex_lock);
> > +	if ((file->f_mode & FMODE_WRITE) &&
> > +	    !(file->f_flags & O_APPEND))
> > +		ftrace_filter_reset(enable);
> >  
> >  	if (file->f_mode & FMODE_READ) {
> >  		struct seq_file *m = file->private_data;
> > 

Re: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

[Steven Rostedt]

On Wed, 22 Jul 2009, Jiri Olsa wrote:

> On Mon, Jul 20, 2009 at 09:11:34PM -0400, Steven Rostedt wrote:
> > 
> > On Thu, 16 Jul 2009, Jiri Olsa wrote:
> > 
> > > If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> > > with read&write permissions, the previous setup will be removed.
> > 
> > This is exactly what it was suppose to do.
> > 
> > man fopen:
> > 
> >        w+     Open for reading and writing.  The file is created  if  it  does
> >               not  exist, otherwise it is truncated.  The stream is positioned
> >               at the beginning of the file.
> > 
> > Which means that if you open a file for "w+" it will truncate it. Hence, 
> > you will remove all previous settings.
> > 
> > What you want is:
> > 
> >        a+     Open for reading and appending (writing at end  of  file).   The
> >               file is created if it does not exist.  The initial file position
> >               for reading is at the beginning  of  the  file,  but  output  is
> >               always appended to the end of the file.
> > 
> > Change the belowe code from "w+" to "a+" and you get your expected result.
> 
> My point was that if you open set_ftrace_filter/set_ftrace_notrace with just O_RDWR
> perm. and will use the file just for reading, the filter will reset.
> 
> You're right about the "w+", there's the O_CREAT|O_TRUNC, sry I missed that.. ;)
> Anyway with "r+" you'll get O_RDWR perm. only, showing the issue:

Ah, then the fix would be to check against O_TRUNC.

-- Steve